Extracellular pH and intracellular phosphatidylinositol 4,5-bisphosphate control Cl currents in guinea pig detrusor smooth muscle cells.

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)P] analog [PI(4,5)P-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)P-diC8, an intriguing finding that underscores the complex nature of Cl channel expression and function in DSM cells. Removal of both extracellular Ca and Mg did not affect the DSM whole cell Cl current, whereas Gd (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, Gd, and PI(4,5)P.