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. 2001 Apr 1;532(Pt 1):73–90. doi: 10.1111/j.1469-7793.2001.0073g.x

Figure 10. cAMP-induced potentiation of L-channels is mediated by PKA: coexistence with the G-protein-dependent inhibition.

Figure 10

A, the protein kinase inhibitors H7 and H89 antagonise the cAMP-induced potentiation. The figure shows current traces recorded at +10 mV in two patches with ATP and opioid agonists in the pipette following incubation with 50 μm 8-CPT-cAMP or 8-CPT-cAMP + 200 μm H7; Vh -40 mV. In the left panel the cAMP-induced potentiation was evident at the low 8-CPT-cAMP concentration (50 μm; Po 0.33 ± 0.03; n = 11 patches). In another 9 cells incubated with 50 μm 8-CPT-cAMP + 200 μm H7 (centre panel) and 6 cells with 1 μm H89 (right panel) the channel activity was depressed and Po was reduced to 0.22 (*P < 0.05) and 0.18 (**P < 0.01), respectively. The two averaged currents to the bottom were calculated over 48 sweeps (cAMP, 4 patches) and 195 sweeps (cAMP + H7, 8 patches). B, H7 and H89 prevent L-channel potentiation induced by forskolin and IBMX. The simultaneous external application of forskolin (10 μm) and IBMX (20 μm) was sufficient to induce L-channel potentiation (left panel). Channel activity at +10 mV was sustained and mean Po increased to 0.36 (11 patches; top right panel). The potentiating effect of forskolin + IBMX was reversed and the agonist-induced inhibition restored in cells incubated with H7 (n = 9) or H89 (n = 6): mean Po was 0.20 (**P < 0.01) and 0.23 (*P < 0.05), respectively (centre panel). H89 and H7 had no effect on basal channel activity: mean Po was 0.19 (n = 8), in both cases. Mean currents were calculated over 67 (left), 69 (centre) and 167 sweeps (right). The top right panel summarises the mean Po obtained with forskolin + IBMX or with H7 and H89 alone. C, the agonist-induced L-channel inhibition persists independently of the cAMP pathway activation. Single L-channel activities at +10 mV (Vh -40 mV) were recorded from patches pre-treated with 200 μm H7 with either the agonists (ATP + opioids) (left) or the antagonists (suramin + naloxone) in the pipette (centre). The mean currents to the bottom were calculated over 180 and 153 sweeps pooled from 7 and 4 patches, respectively. Right, mean Po at +10 mV calculated from n = 27 patches (agonists), n = 11 (agonists + H7), n = 4 (antagonists + H7) (**P < 0.01) and n = 5 (PTX + H7) (**P < 0.01).