Membrane potential, Ca2+ influx, and Ca2+ release in single vascular muscle cells

Isolated single vascular muscle cells from azygous vein of rats were used to make measurements of intracellular Ca2+ release, using a differential interference contrast 2 wavelength system and the Ca2+ indicator arsenazo III (Az III). Ca2+ release in spontaneously contracting isolated single muscle cells was extremely nonuniform, giving Ca2+ signals in some areas that were at least five times as great as those in others. Some areas of the cell showed virtually no detectable increase in Ca2+ activity during contraction, and these differences in Ca2+ activity corresponded with differences in contractile filament movement within the cell. The possibility that the nonuniformity of the Ca2+ signals was due to localization of Az III, which had been introduced by liposomes, was excluded because optical density at the 580 nm isosbestic point in any 5-20 micron 2 area varied by not greater than 50% from the average Az III concentration. In contrast, when isolated single vascular muscle cells were stimulated with electric current pulses, Ca2+ release and contraction were uniformly synchronized throughout the cell. Our data suggest that the uptake and removal process by intracellular transport is the major determinant of intracellular Ca2+ activity in azygous venous vascular muscle cells.