Cl− channels serve as key regulators of excitability and contractility in vascular, intestinal, and airway smooth muscle cells. We recently reported a Cl− conductance in detrusor smooth muscle (DSM) cells. Here, we used the whole cell patch-clamp technique to further characterize biophysical properties and physiological regulators of the Cl− current in freshly isolated guinea pig DSM cells. The Cl− current demonstrated outward rectification arising from voltage-dependent gating of Cl− channels rather than the Cl− transmembrane gradient. An exposure of DSM cells to hypotonic extracellular solution (Δ 165 mOsm challenge) did not increase the Cl− current providing strong evidence that volume-regulated anion channels do not contribute to the Cl− current in DSM cells. The Cl− current was monotonically dependent on extracellular pH, larger and lower in magnitude at acidic (5.0) and basic pH (8.5) values, respectively. Additionally, intracellularly applied phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] analog [PI(4,5)P2-diC8] increased the average Cl− current density by approximately threefold in a voltage-independent manner. The magnitude of the DSM whole cell Cl− current did not depend on the cell surface area (cell capacitance) regardless of the presence or absence of PI(4,5)P2-diC8, an intriguing finding that underscores the complex nature of Cl− channel expression and function in DSM cells. Removal of both extracellular Ca2+ and Mg2+ did not affect the DSM whole cell Cl− current, whereas Gd3+ (1 mM) potentiated the current. Collectively, our recent and present findings strongly suggest that Cl− channels are critical regulators of DSM excitability and are regulated by extracellular pH, Gd3+, and PI(4,5)P2.
Extracellular pH But Not Osmotic Pressure Modulates Cl− Current in Freshly-Isolated Guinea Pig Detrusor Smooth Muscle Cells
