Voltage-dependent large conductance channels in visceral smooth muscle

The ionic conductances that underlie the resting membrane potential of visc eral smooth muscle are not fully understood. Using the patch-clamp techniqu e in the whole-cell configuration, single large conductance channels (LCCs) with unitary conductances of up to 400 pS were recorded in isolated smooth muscle cells of the opossum esophagus, These channels were active at physi ological potentials (-100 to -40 mV) and opened with increasing frequency a s the membrane potential was hyperpolarized, This voltage dependence gave r ise to an inwardly rectifying macroscopic current which was half-maximally activated at -65 mV, The current through LCCs was carried by cations becaus e reduction of external [NaCl] shifted the reversal potential of the LCC cu rrent towards the predicted Nernst potential for a nonselective cation curr ent. These results suggest that LCCs may contribute to resting membrane pot ential in the circular muscle of the opossum esophagus, (C) 1999 Academic P ress.