VOLTAGE CONTROL OF CALCIUM TRANSIENTS ELICITED BY CAFFEINE AND TETRACAINE IN CULTURED RAT MUSCLE-CELLS

Cultured hind limb skeletal muscle cells from newborn rats were used t o study the effect of caffeine and tetracaine upon intracellular Ca2release under voltage or current clamp conditions. Free [Ca2+](i) was measured using the fluorescent calcium-sensitive dye Fluo-3. A field c ontaining one or several myotubes was observed with a video camera and image analysis of fluorescence changes was performed. Addition of 100 -500 mu M tetracaine to the external saline elicited strong fluorescen ce responses in non-clamped cells, but significantly lower responses i n cells clamped at -90 mV. At the same time, tetracaine inhibited volt age induced calcium release. Voltage and tetracaine modulation over th e action of caffeine (500 mu M) was also observed. Pretreatment of cel ls with 10 mu M nifedipine abolished the caffeine induced fluorescence response in non-clamped cells, These findings suggest that, in cultur ed muscle cells, calcium release through the caffeine and tetracaine s ensitive pathways is controlled by both membrane potential and the dih ydropyridine receptor.