ABSTRACT
Calcium-activated chloride currents (ICl(Ca)) have been recorded in many smooth muscle preparations including vascular, airway, intestinal, and urogenital tissues (see Ref. 1). In unstimulated smooth muscle the resting chloride permeability is low (2) and the intracellular chloride concentration (or more accurately the activity) is higher than is expected from passive distribution. As a consequence, the chloride equilibrium potential is much more positive than the normal resting membrane potential in smooth muscle. Consequently any stimulus that increases the Cl conductance will produce Cl ion efflux and depolarization, with subsequent opening of voltage-dependent Ca2þ channels to produce contraction. Several Cl conductances have been described in smooth muscle (3), and one of the most widely expressed currents is ICl(Ca).
