Extracellular pH and Intracellular Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) 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 (71 - 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 (Delta 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 (85) values, respectively. Additionally, intracellularly applied phosphatidylinositol 4.5-bisphosphate [P](4,5)P-2] analog [PI(4,5)P-2-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-2-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)P-2.