Extracellular pH But Not Osmotic Pressure Modulates Cl− Current in Freshly-Isolated Guinea Pig Detrusor Smooth Muscle Cells

We recently characterized Cl currents in freshly isolated guinea pig detrusor smooth muscle (DSM) cells and hypothesized that Cl- conductance plays a critical role in regulation of urinary bladder excitability and contractility. A robust voltage-dependence with midpoint of activation at positive voltages and outward rectification, insensitivity to a physiological intracellular Ca2+ concentration, and Cl- selectivity suggested that ClC channels/antiporters activation underlies Cl- current in freshly-isolated guinea pig DSM cells. Depending on the type, ClC Cl- current can be modulated by an extra- and/or intra-cellular pH. Here we used the whole-cell patch-clamp technique at conditions optimized for Cl- conductance to examine the modulatory effect of external pH on Cl- current in freshly-isolated guinea pig DSM cells. Elevating extracellular pH from 7.4 to 8.5 caused a reversible reduction in Cl- current of 22.4 ± 4.9 % at +100 mV (number of cells n=11, number of animals N=3, p<0.05). Decreasing pH from 7.4 to 6.0 had no effect (n=8, N=3, p>0.05) and further decrease of pH to 5.0 caused a reversible increase in the Cl- current of 32.4 ± 10.9 % (n=11, N=3, p<0.05). ClC-3 or ClC-7 channels/antiporters fit this pH sensitivity profile in guinea pig DSM cells. ClC-3 is thought to be a volume-regulated channel. However, a replacement of control extracellular solution (347 mOms) with hypotonic solution (182 mOsm) mimicking a cell volume increase via osmotic pressure reduction caused no change in Cl- current (n=5, N=3, p>0.05). The data suggest that ClC-7 rather than ClC-3 is the most likely candidate for Cl- conductance in freshly-isolated guinea pig DSM cells. Supported by NIH R01-DK106964 grant to Georgi V. Petkov.