Regulation of Calcium Concentration in Voltage-Clamped Smooth Muscle Cells

Abstract

The regulation of intracellular calcium concentration in single smooth muscle cells was investigated by simultaneously monitoring electrical events at the surface membrane and calcium concentration in the cytosol. Cytosolic calcium concentration rose rapidly during an action potential or during a voltage-clamp pulse that elicited calcium current; a train of voltage-clamp pulses caused further increases in the calcium concentration up to a limit of approximately 1 microM. The decline of the calcium concentration back to resting levels occurred at rates that varied with the calcium concentration in an apparently saturable manner. Moreover, the rate of decline at any given calcium concentration was enhanced after a higher, more prolonged increase of calcium. The process responsible for this enhancement persisted for many seconds after the calcium concentration returned to resting levels. Thus, the magnitude and duration of a calcium transient appear to regulate the subsequent calcium removal.

Effects of lemakalim on changes in Ca2+concentration and mechanical activity induced by noradrenaline in the rabbit mesenteric artery

“…Under these conditions, the background fluorescence intensity was 10-15% of the Fura 2 signals in smooth muscle strips at either excitation wavelength. Cytosolic Ca2+ concentrations were calculated with the formula described by Grynkiewicz et al (1985) and using in vitro calibration (Poenie et al, 1986;Becker et al, 1989). The ratio of maximum (FmaJ to minimum fluorescence (Fmin) was determined in the calibration solution after subtraction of background excited by either 340 or 380 nm and the 380 signals of Fura 2 were assumed to decrease by 15% in the cell due to the possible intracellular viscosity effects of the dye (Becker et al, 1989).…”

“…Cytosolic Ca2+ concentrations were calculated with the formula described by Grynkiewicz et al (1985) and using in vitro calibration (Poenie et al, 1986;Becker et al, 1989). The ratio of maximum (FmaJ to minimum fluorescence (Fmin) was determined in the calibration solution after subtraction of background excited by either 340 or 380 nm and the 380 signals of Fura 2 were assumed to decrease by 15% in the cell due to the possible intracellular viscosity effects of the dye (Becker et al, 1989). The Kd value for Fura 2 was estimated to be 200 nm (Becker et al, 1989 Experiments on chemically skinned smooth muscle…”

Mitochondrial regulation of the cytosolic Ca2+ concentration and the InsP3‐sensitive Ca2+ store in guinea‐pig colonic smooth muscle

“…2) have been reported in several cell types, including smooth muscle (Becker et al 1989). They may arise from a facilitated Ca¥ uptake into the SR (Baro et al 1993).…”

Effects of pinacidil on contractile proteins in high K+‐treated intact, and in β‐escin‐treated skinned smooth muscle of the rabbit mesenteric artery

“…) to the minimum fluorescence (Fmin) was determined in the calibration solution after subtraction of background excited by either 340 or 380 nm. The signals excited by 380nm u.v.-light were assumed to decrease by 15% in the cell due to the possible intracellular viscosity effects on the dye (Becker et al, 1989). The Kd value for Fura-2 was estimated to be 200nm (Becker et al, 1989).…”

“…Under these conditions, the background fluorescence intensity was 10-15% of the Fura-2 signals in smooth muscle strips at either excitation wave length. Cytosolic Ca2+ concentrations were calculated by the formula of Grynkiewicz et al (1985) and using in vitro calibration (Poenie et al, 1986;Becker et al, 1989). The ratio of the maximum (F,.…”