Ca-i(2+)-dependent membrane currents in vascular smooth muscle cells of the rabbit

The membrane potential in vascular smooth muscle cells contributes to the r egulation of cytosolic [Ca2+], which in turn regulates membrane potential b y means of Ca-i(2+)-dependent ionic currents. We investigated the character istics of Ca-i(2+)-dependent currents in rabbit coronary and pulmonary arte rial smooth muscle cells. Ca-i(2+)-dependent currents were recorded using t he whole-cell patch-clamp technique while cytosolic [Ca2+] was increased by caffeine. The reversal potentials of caffeine-induced currents were betwee n -80 and -10 mV under normal ionic conditions, whereas they were about 0 m V when K+-free NaCl solutions were used both in pipette and bath. The total substitution of extracellular Na+ with membrane-impermeable cation N-Methy l-D-glucamine did not affect caffeine-induced currents, implying no signifi cant contribution of Na+ as a permeant ion to the currents. The substitutio n of extracellular NaCl with sucrose reduced outward component of the curre nts and shifted the reversal potentials according to the change in Cl- equi librium potential. Upon application of the niflumic acid under K+-free cond itions, most of the current induced by caffeine was inhibited. Taken togeth er, the results of the present study indicate that K+ and Cl- currents are major components of Ca-i(2+)-dependent currents in vascular smooth muscles isolated from coronary and pulmonary arteries of the rabbit, and the relati ve contribution of each type of current to total currents are not different between the two arteries. (C) 2001 Elsevier Science Inc. All rights reserv ed.