Properties of single-channel and whole cell Cl− currents in guinea pig detrusor smooth muscle cells

Multiple types of Cl − channels regulate smooth muscle excitability and contractility in vascular, gastrointestinal, and airway smooth muscle cells. However, little is known about Cl − channels in detrusor smooth muscle (DSM) cells. Here, we used inside-out single channel and whole cell patch-clamp recordings for detailed biophysical and pharmacological characterizations of Cl − channels in freshly isolated guinea pig DSM cells. The recorded single Cl − channels displayed unique gating with multiple subconductive states, a fully opened single-channel conductance of 164 pS, and a reversal potential of −41.5 mV, which is close to the E Cl of −65 mV, confirming preferential permeability to Cl − . The Cl − channel demonstrated strong voltage dependence of activation (half-maximum of mean open probability, V 0.5 , ~−20 mV) and robust prolonged openings at depolarizing voltages. The channel displayed similar gating when exposed intracellularly to solutions containing Ca 2+ -free or 1 mM Ca 2+ . In whole cell patch-clamp recordings, macroscopic current demonstrated outward rectification, inhibitions by 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS) and niflumic acid, and insensitivity to chlorotoxin. The outward current was reversibly reduced by 94% replacement of extracellular Cl − with I − , Br − , or methanesulfonate (MsO − ), resulting in anionic permeability sequence: Cl − >Br − >I − >MsO − . While intracellular Ca 2+ levels (0, 300 nM, and 1 mM) did not affect the amplitude of Cl − current and outward rectification, high Ca 2+ slowed voltage-step current activation at depolarizing voltages. In conclusion, our data reveal for the first time the presence of a Ca 2+ -independent DIDS and niflumic acid-sensitive, voltage-dependent Cl − channel in the plasma membrane of DSM cells. This channel may be a key regulator of DSM excitability.