Figure 2. hKSper currents are insensitive to intracellular alkalinization.
(A) Representative KSper currents were recorded from sperm cells in response to voltage ramps as shown. Recordings were done with various pHi as indicated. The bath solution containing 1 mM Ca2+ was used to inhibit K+ current through CatSper (left panels). Right panels show traces in divalent free conditions, which allow K+ current through CatSper. Intracellular alkalinization was evoked by addition of 10 mM NH4Cl to the bath (red traces). A weak intracellular buffer (5 mM of HEPES or MES) allowed instantaneous pH changes. Zn2+ was used to block H+ currents via Hv1 at acidic intracellular pH. The upper panels and the lower panels are recordings from two different sperm cells. (B) KSper and CatSper/KSper current densities (CDs) recorded from sperm cells as shown in (A). At pHi 7.4 KSper CDs were: 45 ± 3 pA/pF (control) and 44 ± 4 pA/pF (plus NH4Cl). These values were similar at pHi 5.5: CDs were: 51 ± 8 pA/pF (control) and 53 ± 4 pA/pF (plus NH4Cl). However, under DVF conditions that permit K+ efflux through CatSper, CDs at pHi 7.4 were: 116 ± 11 pA/pF (control) and 231 ± 26 pA/pF (plus NH4Cl). At pHi 5.5, CDs were: 85 ± 5 pA/pF (control) and 341 ± 21 pA/pF (plus NH4Cl). Shown are CDs acquired at +120 mV and presented as mean ± SEM; n = 4–6 independent experiments with cells from four different human donors.