Hypotonic swelling increases L-type calcium current in smooth muscle cellsof the human stomach

The purpose of the present study was to characterize the Ca2+ channels in s mooth muscle cells from human stomach and to examine the effects of osmotic swelling on the channel activity. Ca2+ channel current with either Ca2+ or Ba2+ as charge carrier was recorded from freshly isolated smooth muscle ce lls using the conventional whole-cell patch clamp technique. The degree of cell swelling as a result of hypotonic challenge was monitored using a vide o image analysis system. The changes in intracellular Ca2+ concentration ([ Ca2+](i)) were measured by microfluorimetry. The pharmacological and voltag e activation profile suggests a typical dihydropyridine-sensitive L-type Ca 2+ current. Cell swelling, induced by hypotonic challenge, enhanced the amp litude of currents through L-type Ca2+ channels without significant effects on steady-state voltage dependency. After treatment with the L-type Ca2+ c hannel agonist Bay K 8644 (0.1-2 mu M), no further significant increase in calcium channel current or corresponding [Ca2+](i) transients were provoked by the swelling. The above results demonstrated that the presence of L-typ e Ca2+ current in smooth muscle cells of the human stomach and the augmenta tion of the current are closely associated with the volume increase resulti ng from hypotonic swelling.