Whole cell current and membrane potential regulation by a human smooth muscle mechanosensitive calcium channel

Mechanotransduction is required for a wide variety of biological functions. The aim of this study was to determine the effect of activation of a mechanosensitive Ca(2+) channel, present in human jejunal circular smooth muscle cells, on whole cell currents and on membrane potential. Currents were recorded using patch-clamp techniques, and perfusion of the bath (10 ml/min, 30 s) was used to mechanoactivate the L-type Ca(2+) channel. Perfusion resulted in activation of L-type Ca(2+) channels and an increase in outward current from 664 +/- 57 to 773 +/- 72 pA at +60 mV. Membrane potential hyperpolarized from -42 +/- 4 to -50 +/- 5 mV. In the presence of nifedipine (10 microM), there was no increase in outward current or change in membrane potential with perfusion. In the presence of charybdotoxin or iberiotoxin, perfusion of the bath did not increase outward current or change membrane potential. A model is proposed in which mechanoactivation of an L-type Ca(2+) channel current in human jejunal circular smooth muscle cells results in increased Ca(2+) entry and cell contraction. Ca(2+) entry activates large-conductance Ca(2+)-activated K(+) channels, resulting in membrane hyperpolarization and relaxation.