Indexed on: 20 Dec '18Published on: 20 Dec '18Published in: American journal of physiology. Cell physiology
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 sub-conductive states, a fully opened single-channel conductance of 164 pS, and a reversal potential of -41.5 mV, which is close to the E of -65 mV, confirming preferential permeability to Cl. The Cl channel demonstrated strong voltage-dependence of activation (V~-20 mV) and robust prolonged openings at depolarizing voltages. The channel displayed similar gating when exposed intracellularly to solutions containing Ca-free, 300 nM Ca, or 1 mM Ca. 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 levels (0, 300 nM, and 1 mM) did not affect the amplitude of Cl current and outward rectification, high Ca slowed voltage-step current activation at depolarizing voltages. In conclusion, our data reveal for the first time the presence of a Ca-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.