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American Journal of Physiology - Renal Physiology logoLink to American Journal of Physiology - Renal Physiology
. 2017 Mar 29;313(2):F254–F261. doi: 10.1152/ajprenal.00102.2017

PGF2α regulates the basolateral K channels in the distal convoluted tubule

Lijun Wang 1,2, Chengbiao Zhang 2, Xiao-Tong Su 2, Dao-Hong Lin 2, Peng Wu 2, Michal L Schwartzman 2, Wen-Hui Wang 2,✉
PMCID: PMC5582901  PMID: 28356287

Abstract

Our aim is to examine the role of PGF2α receptor (FP), a highly expressed prostaglandin receptor in the distal convoluted tubule (DCT) in regulating the basolateral 40-pS K channel. The single-channel studies demonstrated that PGF2α had a biphasic effect on the 40-pS K channel in the DCT–PGF2α stimulated at low concentrations (less than 500 nM), while at high concentrations (above 1 µM), it inhibited the 40-pS K channels. Moreover, neither 13,14-dihydro-15-keto-PGF2α (a metabolite of PGF2α) nor PGE2 was able to mimic the effect of PGF2α on the 40-pS K channel in the DCT. The inhibition of PKC had no significant effect on the 40-pS K channel; however, it abrogated the inhibitory effect of 5 µM PGF2α on the K channel. Moreover, stimulation of PKC inhibited the 40-pS K channel in the DCT, suggesting that PKC mediates the inhibitory effect of PGF2α on the 40-pS K channel. Conversely, the stimulatory effect of PGF2α on the 40-pS K channel was absent in the DCT treated with DPI, a NADPH oxidase (NOX) inhibitor. Also, adding 100 µM H2O2 mimicked the stimulatory effect of PGF2α and increased the 40-pS K channel activity in DCT. Moreover, the stimulatory effect of 500 nM PGF2α and H2O2 was not additive, suggesting the role of superoxide-related species in mediating the stimulatory effect of PGF2α on the 40-pS K channel. The inhibition of Src family tyrosine protein kinase (SFK) not only inhibited the 40-pS K channel in the DCT but also completely abolished the stimulatory effects of PGF2α and H2O2 on the 40-pS K channel. We conclude that PGF2α at low doses stimulates the basolateral 40-pS K channel by a NOX- and SFK-dependent mechanism, while at high concentrations, it inhibits the K channel by a PKC-dependent pathway.

Keywords: Kcnj10, Kcnj16, cyclooxygenase, PKC, NCC

the distal convoluted tubule (DCT) is responsible for the reabsorption of 5–9% of filtered Na load and is the target for thiazide diuretics (7, 8, 14, 24). The DCT is generally divided into the early part (DCT1) and the late portion (DCT2). While thiazide-sensitive NCC is expressed in the apical membrane of both DCT1 and DCT2, the channel activity of ROMK and epithelial Na channel (ENaC) is only detected in the apical membrane of DCT2, although ROMK immunostaining is also detected in DCT1 (3, 7, 40). The reabsorption of NaCl in the DCT1 is a two-step process. Na and Cl enter the cells across the apical membrane through the NCC, and Na is then pumped out of the cell through the basolateral Na-K-ATPase, while Cl exits the cell along its electrochemical gradient by basolateral Cl channels (ClC-kb) or KCl cotransporter (19, 22, 39, 44). In the DCT2, Na enters the cell across the apical membrane through both NCC and ENaC (18, 33). The basolateral K channel in DCT1 and DCT2 plays an important role in generating the cell membrane potential and in maintaining K recycling across the basolateral membrane, which is known to be essential for sustaining Na-K-ATPase activity (11, 41). Previous patch-clamp experiments have reported that a 40-pS K channel is the only type of K channels in the basolateral membrane of DCT (20, 47). The notion that Kir4.1 is a key component for forming the basolateral K conductance in the DCT was convincingly established by the finding that the disruption of Kcnj10 (Kir.4.1) completely eliminated the expression of the 40-pS K channel in the basolateral membrane of the DCT (48). Furthermore, we demonstrated that the basolateral Kir4.1 channel activity determines the expression of NCC in the DCT (6, 48). Thus, the regulation of the basolateral K channels in the DCT should have a profound effect on transcellular Na transport. However, the regulatory mechanism of the basolateral K channels in the DCT is not well investigated.

Previous studies have demonstrated that cyclooxygenase (COX), which converts arachidonic acid to prostaglandins, such as PGE2 and PGF2α, is expressed in the DCT (9). The possibility that COX-dependent metabolites of arachidonic acid play a role in the regulation of renal Na transport is strongly suggested by the fact that inhibiting COX with nonsteroidal anti-inflammatory drugs decreases renal Na excretion (9). Previous experiments have shown that PGF2α receptors (FP) are highly expressed in the DCT (10, 31). However, the role of PGF2α in the regulation of the basolateral K channels has not been tested. Thus, the aim of the present study is to examine the effect of PGF2α on the basolateral 40-pS K channels of the DCT.

MATERIALS AND METHODS

Preparation of DCT.

The experiments were performed in 4- to 6-wk-old male and female C57BL/6 mice purchased from the Jackson Laboratory (Bar Harbor, ME), following an Institutional Animal Care and Use Committee-approved protocol in accordance with the NIH guidelines for the care and use of laboratory animals. As we did not find the sex differences regarding the effect of PGF2α, the data are obtained and presented from both male and female animals. The mice were kept on a normal diet and had free access to water. We perfused the left kidney with 5 ml collagenase (Worthington CLS II, 1 mg/1 ml) containing L-15 medium (Life Technologies, Carlsbad, CA) immediately after the mice were euthanized by cervical dislocation. The renal cortex was cut into small pieces after removal of the kidney, and then the tissues were incubated in collagenase-containing L-15 medium at 37°C for 45–60 min. After being rinsed with L-15 medium, the DCTs were dissected in an ice-cold media. The isolated DCTs were placed on a cover glass coated with polylysine (Sigma, St. Louis, MO) for patch-clamp experiments. The DCTs were superfused with HEPES-buffered solution containing (in mM) 140 NaCl, 5 KCl, 1.8 MgCl2, 1.8 CaCl2, and 10 HEPES (pH = 7.4) at room temperature for the single-channel recording. All animal procedures were approved by the Institutional Animal Care and Use Committee of New York Medical College.

Patch-clamp experiments.

We used borosilicate glass (1.7-mm OD) to make the patch-clamp pipettes, and the pipettes were pulled with a Narishige electrode puller. The pipette had a resistance of 2–4 MΩ when filled with 140 mM KCl. For the perforated whole cell recording, the tip of the pipette was filled with pipette solution containing 140 mM KCl, 2 mM MgCl2, 1 mM EGTA, and 5 mM HEPES (pH 7.4), and the pipette was then back-filled with amphotericin B (20 μg/0.1 ml) containing the pipette solution. The bath solution contains (in mM) 140 KCl, 1.8 MgCl2, 1.8 CaCl2, and 10 HEPES (pH = 7.4). After forming a high-resistance seal (>2 GΩ), the membrane capacitance was monitored until the whole cell patch configuration was formed. The K currents were measured by an Axon 200A patch-clamp amplifier. The currents were low-pass filtered at 1 kHz, digitized by an Axon interface (Digidata 1322), and data were analyzed using the pClamp software system 10 (Axon).

For the single-channel recording, we used Axon 200B patch-clamp amplifier and Axon interface as described above. The pipette solution for the single-channel recording was composed of (in mM) 140 KCl, 1.8 MgCl2, and 10 HEPES (pH = 7.4), and the bath solution contained 140 mM Na and 5 mM KCl, as described above. The currents were low-pass filtered at 1 kHz and digitized by an Axon interface. Data were analyzed using the pClamp software system 10 (Axon). Channel activity defined as NPo (a product of channel number and open probability) was calculated from data samples of 60-s duration in the steady state as follows: NPo = Σ (t1 + 2t2 +... iti), where ti is the fractional open time spent at each of the observed current levels. All patch-clamp experiments were performed in the early part of DCT.

Experimental materials and statistics.

PGF2α, PGE2, and PGFM were obtained from Cayman Chemical (Ann Arbor, MI), whereas phorbol 12-myristate 13-acetate (PMA), Gö 6976, diphenyleneiodonium sulfate (DPI), and 4-amino-5-(4-methylphenyl)-7-(t-butyl) pyrazolo[3,4-d]-pyrimidine (PP-1) were purchased from Sigma (St. Louis, MO). Collagenase type 2 was purchased from Worthington (Lakewood, NJ). The data are shown as means ± SE, and a Student's t-test or one-way ANOVA was used to determine the statistical significance.

RESULTS

We first examined the effect of PGF2α on the basolateral 40-pS K channel, which is known to be composed of Kir4.1 and Kir5.1 in the DCT (36). Figure 1 is a recording made in a cell-attached patch showing the K channel activity before and after the application of 5 μM PGF2α. Under control conditions, there were at least five levels of the 40-pS K channel in the basolateral membrane of the DCT and the channel activity, defined by NPo, was 2.52. From five experiments, the channel open probability (Po) was calculated to be 0.50 ± 0.1, a value that was consistent with those reported previously (47). Adding 5 μM PGF2α inhibited the 40-pS K channel in the DCT within 5 min, and the inhibitory effect of PGF2α was reversible because washout restored the channel activity. From eight similar experiments, we observed that the addition of 5 μM PGF2α reversibly decreased the K channel activity (NPo) from 1.85 ± 0.2 to 0.31 ± 0.11 (Fig. 2).

Fig. 1.

Fig. 1.

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PGF2α at high concentrations inhibits the basolateral 40-pS K channel in the distal convoluted tubule (DCT). A channel recording shows the effect of 5 µM PGF2α on the basolateral 40-pS K channels in the DCT. The experiment was performed in a cell-attached patch, and holding potential was 0 mV. The top trace shows the time course of the experiments, and three parts of the recording indicated by numbers are extended to show the fast time resolution. The channel closed level was indicated by a dotted line and “C,” and the arrows indicate the addition of PGF2α and washout separately. The pipette solution contained 140 mM KCl, 1.8 mM MgCl2, and 10 mM HEPES (pH = 7.4), and the bath solution was composed of 140 mM NaCl, 5 mM KCl, 1.8 mM CaCl2, 1.8 mM MgCl2, and 10 mM HEPES (pH = 7.4).

Fig. 2.

Fig. 2.

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Dose-response curves of PGF2α, PGFM, and PGE2 effect on the basolateral 40-pS K channel in the DCT. The experiments were performed in cell-attached patches, and the channel activity was determined at 0 mV holding potential. The DCT was bathed in a solution containing 140 mM NaCl/5 mM KCl, and the pipette solution contained 140 mM KCl. “*” indicates a significant difference (P < 0.05) between the control and experimental groups (n = 5–7).

We next examined the dose response of PGF2α effect on the 40-pS K channel in the DCT using the single-channel recording. Figure 2 is a dose-response curve of PGF2α effect showing that PGF2α is still able to inhibit the 40-pS K channel at concentrations as low as 1 μM (NPo = 0.8 ± 0.2). In contrast, PGF2α at low concentrations has a stimulatory effect on the 40-pS K channel activity. Figure 3 is a recording showing that adding 500 nM of PGF2α significantly stimulated the 40-pS K channel in the DCT and increased NPo to 2.7 ± 0.4 within 5 min (n = 9). Thus, the effect of PGF2α on the 40-pS K channel is biphasic: PGF2α at low concentrations (200–500 nM) stimulated the basolateral 40 pS K channel in the DCT, while at concentrations above 1 μM, it inhibited the 40-pS K channel.

Fig. 3.

Fig. 3.

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PGF2α at low concentrations stimulates the basolateral 40-pS K channel in the DCT. A channel recording shows the effect of 500 nM PGF2α on the basolateral 40-pS K channels in the DCT. The experiment was performed in a cell-attached patch and holding potential was 0 mV. The top trace shows the time course of the experiments, and two parts of the traces indicated by numbers are extended to show the fast time resolution. The channel closed level was indicated by a dotted line and “C,” and the arrow indicates the addition of PGF2α. The solutions in the bath and the pipette were the same as described in Fig. 1.

We next examined whether the effect of PGF2α on the 40-pS K channel was specific by testing the effect of PGE2 and PGF2α metabolite, 13,14-dihydro-15-keto-PGF2α (PGFM), on the 40-pS K channel in the DCT (13). Figure 2 summarizes the results from five experiments, in which the effects of PGFM or PGE2 on the K channel activity were examined with different concentrations (control NPo, 1.7 ± 0.2; 500 nM PGFM, 1.73 ± 0.2; and 5 μM PGFM, 1.75 ± 0.3; n = 5). Also, application of PGE2 had no effect on the 40-pS K channel in the DCT (control NPo, 1.8 ± 0.2; 500 nM PGE2, 1.68 ± 0.2; 5 μM PGE2, 1.65 ± 0.3; n = 5). Thus, neither PGFM nor PGE2 mimicked the effects of PGF2α and failed to affect the 40-pS K channel activity in the basolateral membrane of the DCT, suggesting that the effect of PGF2α on the 40-pS K channel was specific and mediated by the FP receptor.

Because the effect of PGF2α on the basolateral K channels was biphasic, it is conceivable that two distinct signaling pathways are involved in mediating the effect of PGF2α. FP receptors are G protein-coupled receptors (Gq), and they have two isoforms: FPA and FPB (27, 28). It has been suggested that two isoforms may activate different second messengers: one pathway is associated with PKC, while the second one is linking with Rho activation (28). Because PKC has been reported to inhibit Kir.4.1/Kir5.1 heterotetramer (29, 45), we next examined whether the inhibitory effect of PGF2α on the 40-pS K channel is mediated by PKC. Thus, we carried out the cell-attached patches to investigate whether the inhibition of PKC abolished the effect of 5 μM PGF2α on the 40-pS K channel. Figure 4A is a recording showing that the inhibition of PKC with 1 μM Gö 6976 had no significant effect on the K-channel activity (Control NPo, 1.85 ± 0.15; Gö 6976, 1.90 ± 0.2). However, in the presence of Gö 6976, PGF2α (5 μM) failed to inhibit the 40-pS K channel. Results summarized in Fig. 4B demonstrate that the channel activity was 2.15 ± 0.25 (n = 6), a value not different from the control. Furthermore, the role of PKC in inhibiting the basolateral K channels in the DCT was also confirmed by the finding that PMA (1 μM) inhibited the K-channel activity (NPo, 0.65 ± 0. 10, n = 6) (Fig. 4B). Therefore, the results strongly suggest that PKC is involved in mediating the inhibitory effect of PGF2α on the 40-pS K channels in the DCT.

Fig. 4.

Fig. 4.

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Suppression of PKC abolished the inhibitory effect of PGF2α on the 40-pS K channel. A: channel recording shows the effect of 5 µM PGF2α on the 40-pS K channel in the DCT treated with Gö 6976 (1 µM). The experiment was performed in a cell-attached patch at 0 mV with 140 mM NaCl/5 mM KCl in the bath and 140 mM KCl in the pipette. The top trace shows the time course of the experiments, and three parts of the recording indicated by numbers are extended to show the fast time resolution. The channel closed level is indicated by a dotted line and “C,” and the arrows indicate the addition of Gö 6976 and PGF2α separately. B: bar graph summarizes the effect of phorbol 12-myristate 13-acetate (PMA; 1 µM) and PGF2α (5 µM) on the 40-pS K channel in the DCT1 treated with or without 1 µM Gö 6976. All experiments were performed in cell-attached patches. The composition of the bath and pipette solutions is described above, and the channel activity was measured at 0 mV.

We then examined the mechanism by which PGF2α stimulates the basolateral K channels in the DCT. It is well established that Rho family GTPases, such as RAC1/RAC2, are potent stimulators of NOX (12). Moreover, reactive oxygen species have been shown to stimulate the protein tyrosine kinase activity such as c-Src (1, 2, 30). Our previous work demonstrated that SFK phosphorylates Kir.4.1, thereby activating the basolateral K-channel activity in the DCT (47). Therefore, we performed cell-attached patches in the isolated DCT to test whether the inhibition of NOX with DPI was able to abolish the stimulatory effect of PGF2α on the K channels. From the inspection of Fig. 5, it is apparent that inhibition of NOX had no significant effect on the 40-pS K-channel activity in the DCT. However, in the presence of DPI (10 μM), adding 500 nM of PGF2α not only failed to stimulate the K-channel activity but also actually inhibited the basolateral 40-pS K channel (Control, 1.82 ± 0.15; DPI, 1.84 ± 0.22; DPI+PGF2α, 0.40 ± 0.05, n = 7) (Fig. 6). Thus, our data strongly suggest that the stimulatory effect of PGF2α on the 40-pS K channels was the result of activating NOX. To test whether the stimulatory effect of PGF2α was mediated by SFK-dependent mechanism, we examined whether the inhibition of SFK abolished the stimulatory effect of PGF2α on the 40-pS K channel. The results summarized in Fig. 6 demonstrate that the inhibition of SFK with PP1 (100 nM) not only decreased the channel activity (NPo = 0.35 ± 0.10) but also completely abolished the stimulatory effect of 500 nM PGF2α (NPo = 0.30 ± 0.08, n = 8). Hence, the results suggest that SFK is responsible for the stimulatory effect of PGF2α on the 40-pS K channels.

Fig. 5.

Fig. 5.

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Suppression of NADPH oxidase (NOX) with DPI abolished the stimulatory effect of PGF2α on the 40-pS K channel. A channel recording shows the effect of 500 nM PGF2α on the 40-pS K channel in the DCT treated with DPI (1 µM). The experiment was performed in a cell-attached patch at 0 mV with 140 mM NaCl/5 mM KCl in the bath and 140 mM KCl in the pipette. The top trace shows the time course of the experiments, and three parts of the recording indicated by numbers are extended to show the fast time resolution. The channel closed level is indicated by a dotted line and “C.”

Fig. 6.

Fig. 6.

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Inhibition of SFK or NOX abrogates the stimulatory effect of PGF2α on the basolateral 40-pS K channel. A bar graph summarizes the experiments in which the effect of 500 nM PGF2α on the 40-pS K channel in the DCT was examined in the presence of 100 nM PP1 (SFK inhibitor) or 1 µM diphenyleneiodonium chloride (DPI). The experiments were performed in a cell-attached patch at 0 mV with 140 mM NaCl/5 mM KCl in the bath and 140 mM KCl in the pipette.

After showing that the stimulatory effect of PGF2α on the basolateral 40-pS K channel was abrogated by inhibiting either NOX or SFK, we examined whether the application of H2O2 was able to mimic the effect of PGF2α, and we stimulated the basolateral 40-pS K channel in the DCT using both perforated whole cell recording and single-channel recording. Figure 7A is a recording showing the Ba2+-sensitive whole cell K currents measured in the DCT, and it shows that 100 μM H2O2 increased the Ba2+-sensitive whole cell K currents at −60 mV from 1400 ± 70 pA under control conditions to 2300 ± 170 pA (n = 6) (Fig. 7B). Figure 7C is a representative single-channel recording showing that 100 μM H2O2 activated the 40-pS K channels and increased the channel activity from 1.75 ± 0.15 to 2.45 ± 0.20 (n = 5) (Fig. 7D). The effect of H2O2 on the 40-pS K channel was most likely the result of stimulating SFK because it failed to increase the channel activity in the presence of PP1 (PP1, 0.30 ± 0.04; PP1+ H2O2, 0.30 ± 0.05, n = 5–9) (Fig. 7D). In addition, H2O2 and PGF2α effects were not additive because H2O2 did not increase the channel activity after the DCT was treated with 500 nM PGF2α (NPo = 2.6 ± 0.3, n = 5). Therefore, the results strongly suggest that PGF2α stimulated the 40-pS K channel by activating the ROS-SFK pathway.

Fig. 7.

Fig. 7.

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H2O2 stimulates the basolateral 40 pS K channel in the DCT. A: whole cell recording shows the Ba2+-sensitive K currents measured with perforated patch under control conditions and in the presence of 100 µM H2O2. The DCT was bathed in 140 mM KCl containing solution, and the pipette solution also contained 140 mM KCl. B: bar graph summarizes the experimental results in Fig. 7A (n = 6). The measurements of the whole cell K currents were performed at −60 mV. C: cell-attached channel recording shows the effect of 100 µM H2O2 on the basolateral 40-pS K channel in the DCT1 with 140 mM NaCl/5 mM KCl in the bath and 140 mM KCl in the pipette at 0 mV. The time course of the experiment is shown (top), and two parts of the data are extended to show the fast time resolution (bottom). D: bar graph summarizes the experiments in which the effect of H2O2 on the basolateral 40 pS K channel was examined in the presence of 100 nM PP1 or 500 nM PGF2α. All experiments were performed in cell-attached patches with 140 mM NaCl/5 mM KCl in the bath and 140 mM KCl in the pipette at 0 mV.

DISCUSSION

The main finding of the present study is that PGF2α modulates the basolateral 40-pS K channels in the DCT. At high concentrations (>1 µM) PGF2α inhibits the basolateral 40-pS K channels in the DCT, whereas at low concentrations, it stimulates the K channels. The biphasic effect of PGF2α on the 40-pS K channel in the DCT is most likely due to the stimulation of two different subtype FP receptors: FPA and FPB, which have been shown to activate PKC and Rho pathway, respectively (27, 28). Two lines of evidence suggest that PKC mediates the inhibitory effect of PGF2α on the 40-pS K channel in the DCT: 1) the inhibition of PKC abolished the effect of 5 μM PGF2α on the 40-pS K channel and 2) the stimulation of PKC inhibited the basolateral K channel. On the other hand, the stimulatory effect of PGF2α on the basolateral 40-pS K channels is possibly mediated by NOX-dependent pathway. This notion is supported by following observations: 1) suppressing NOX abolished the stimulatory effect of PGF2α on the 40-pS K channels in the DCT; 2) adding H2O2 increased the 40 pS K channels activity; and 3) the stimulatory effect of H2O2 and PGF2α on the 40-pS K channel in the DCT was not additive, suggesting both compounds stimulate the K channel by a same mechanism. Moreover, the observation that the inhibition of SFK abolished the stimulatory effect of PGF2α or H2O2 on the K channel in the DCT strongly suggests that SFK mediates the stimulatory effect of both PGF2α and H2O2 on the 40-pS K channel. Also, the observation that neither PGE2 nor PGFM is able to mimic the effect of PGF2α suggests that only PGF2α plays a role in the regulation of the basolateral 40-pS K channel in the DCT.

It is well established that the basolateral 40-pS K channel in the DCT is composed of Kir4.1 and Kir5.1 (20). Moreover, Kir4.1 plays a key role in providing the K conductance of Kir4.1/5.1 heterotetramer, while Kir5.1 is most likely a regulatory subunit (36). Although Kir.4.1 is expressed also in the basolateral membrane of nephron segments other than in the DCT (15, 37, 46), only in the DCT does it play a dominant role in determining the basolateral K conductance. Our previous experiments demonstrated the disruption of Kir.4.1 in the DCT almost completely eliminated basolateral K conductance and caused a large depolarization of the membrane (48). Thus, it is conceivable that PGF2α-induced stimulation of the 40-pS K channels should increase, whereas PGF2α-induced inhibition of the K channel is expected to decrease the negativity of DCT membrane potential.

The application of PGF2α in the rat kidney has been shown to increase urinary Na excretion (35, 42). We speculate that PGF2α-induced natriuretic effect may be partially mediated by inhibiting the basolateral Kir4.1/Kir5.1 heterotetramer in the DCT. We postulate that the inhibition of the basolateral 40-pS K channel in the DCT by PGF2α should decrease the negativity of the DCT membrane (depolarization). Because the membrane potential provides the driving force for Cl exit across the basolateral Cl channels, a decrease in the basolateral K conductance should diminish Cl exit from the DCT, thereby increasing intracellular Cl concentrations. It has been suggested that the intracellular Cl concentration plays a role in the regulation of NCC activity, such that high Cl concentration inhibits, whereas low Cl concentration stimulates NCC activity (38). The Cl−-sensitive regulation of NCC activity is the result of the modulation of the with-no-lysine kinase (WNK) because WNK1 and WNK4 are Cl−-sensitive kinases (4, 25). A large body of evidence has convincingly demonstrated that WNK, ste20-proline-alanine rich kinase (SPAK) and oxidative-sensitive responsive kinase (OSR) play key roles in stimulating NCC expression and activity (16, 17, 21, 26, 43). It is now generally accepted that WNK phosphorylates and activates SPAK or OSR which, in turn, stimulates NCC activity by phosphorylation (26, 32). Thus, it is conceivable that PGF2α-induced inhibition of the basolateral K-channel activity should suppress the activity of WNK and SPAK. This speculation is supported by previous findings that the disruption of Kir.4.1 inhibited basolateral Cl conductance and down-regulated the expression of SPAK (6, 48).

The physiological importance of PGF2α-induced inhibition of the 40-pS K channel is suggested by the previous report that high potassium intake selectively increased PGF2α formation in the kidney (23). It is well established that high K and Na intake decreases NCC expression (5, 34, 38). High K-induced inhibition of NCC should increase Na and volume delivery into the late part of aldosterone-sensitive distal nephron, thereby, stimulating K excretion in the connecting tubule and the cortical collecting duct. Thus, high K intake-induced inhibition of NCC plays a key role in regulating renal K excretion and body K homeostasis. Because the basolateral Kir4.1 activity determines the activity of NCC (6), it is possible that an increase in PGF2α generation induced by high K intake might be involved in the downregulation of NCC by inhibiting Kir4.1 in the DCT, thereby increasing renal K excretion.

Conversely, PGF2α-induced stimulation of the 40-pS K channel should augment the basolateral K conductance, thereby, increasing the negativity of DCT membrane. Our unpublished observations show that a decrease in K intake or Na restriction stimulates the basolateral K conductance in the DCT (Wang L., unpublished observations). This is consistent with the report that Na restriction and K depletion increases NCC activity by a WNK–SPAK-dependent pathway (5, 38). However, the evidence that shows the correlation between dietary K intake and changes in PGF2α concentrations is still absent, and further experiments are required to examine the role of PGF2α in mediating the effect of K depletion on the 40-pS K channel in the DCT. In summary, PGF2α has a biphasic effect on the basolateral 40-pS K channel in the DCT. It is possible that PGF2α may play a role in mediating the effect of dietary Na and K intake on the membrane transport by modulating the basolateral K channels in the DCT.

GRANTS

This work is supported by National Institutes of Health Grants DK-54983 (to W.-H. Wang), HL-34100 (to M. L. Schwartzman), National Natural Science Foundation of China Grant (no. 31500939) (to L. J. Wang), and Heilongjiang Postdoctoral Foundation (no. LBH-Z15183) (to L. J. Wang).

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

AUTHOR CONTRIBUTIONS

L.W. and W.-H.W. conceived and designed research; L.W., C.Z., X.-T.S., and P.W. performed experiments; L.W., C.Z., and W.-H.W. analyzed data; L.W., C.Z., and W.-H.W. interpreted results of experiments; L.W., C.Z., and W.-H.W. prepared figures; L.W. and W.-H.W. drafted manuscript; L.W., M.L.S., and W.-H.W. edited and revised manuscript; C.Z., X.-T.S., P.W., M.L.S., and W.-H.W. approved final version of manuscript.

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