The purpose of the present study was to characterize the Ca2+ channels in smooth
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 cells using the conventional
whole-cell patch clamp technique. The degree of cell swelling as a result of hypotonic
challenge was monitored using a video image analysis system. The changes in
intracellular Ca2+ concentration ([Ca2+]i) were measured by microfluorimetry. The
pharmacological and voltage activation profile suggests a typical
dihydropyridine-sensitive L-type Ca2+ current. Cell swelling, induced by hypotonic
challenge, enhanced the amplitude of currents through L-type Ca2+ channels without
significant effects on steady-state voltage dependency. After treatment with the
L-type Ca2+ channel agonist Bay K 8644 (0.1-2 µM), 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-type Ca2+ current in
smooth muscle cells of the human stomach and the augmentation of the current are
closely associated with the volume increase resulting from hypotonic swelling.
Experimental Physiology (2000) 85.5, 497-504.