Modulation of ionic currents in smooth muscle balls of the rabbit intestine by intracellularly perfused ATP and cyclic AMP

Whole-cell voltage clamp and intracellular perfusion technique on single smooth muscle cells

Using freshly isolated single smooth muscle cells prepared by collagenase treatment, membrane currents were recorded by whole-cell voltage clamp. Intracellular constituents were modified by using an intracellular perfusion technique, i.e., pipette solutions were continuously exchanged from control to test solutions during current recording. In smooth muscle cells, intracellular application of ATP, but not cyclic AMP, enhanced the amplitude of Ca2+ currents and prevented current run-down. In addition, with this stabilization of Ca2+ current recording by ATP, introduction of various chemicals into the cell using the intracellular perfusion technique is useful for investigations of regulation of ion channels in smooth muscle cells.

Regulation of calcium current by intracellular calcium in smooth muscle cells of rabbit portal vein

Effects of concentrations of intracellular calcium, [Ca2+]i, on the voltage-dependent Ca2+ current (ICa) recorded from dispersed single smooth muscle cells of the rabbit portal vein were studied, using a whole cell voltage clamp method combined with an intracellular perfusion technique. Outward currents were minimized by replacement of Cs+ -rich solution in the pipette and 20 mM tetraethylammonium in the bath. The ICa was evoked by command pulses of above -30 mV, and the maximum amplitude was obtained at about 0 mV. This ICa was dose dependently inhibited by increases in the [Ca2+]i above 30 nM. The Kd value of the [Ca2+]i required to inhibit the ICa was about 100 nM. The Ba2+ current was also inhibited by increases in the [Ca2+]i. Conversely, perfusion of Ba2+ into the cell up to 100 microM did not suppress the ICa. Changes in the [Ca2+]i did not modify the steady-state inactivation curve. The inhibition of the ICa evoked by the test pulse is most prominent when the preceding influx of Ca2+ during the conditioning pulse was large, as estimated using a double pulse protocol. This inhibition was proportionally reduced by increases in the concentration of the Ca2+ chelator, ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). Therefore, the Ca2+ -dependent inactivation of the Ca2+ channel may contribute toward regulating [Ca2+]i in smooth muscle cells of the rabbit portal vein.