General physiology and biophysics. vol:9 issue:3 pages:251-66
Antipyrylazo III myoplasmic calcium transients were recorded in cut skeletal muscle fibres of the frog (Rana esculenta), using the double vaseline-gap voltage-clamp system. Intracellular calcium removal mechanisms were analysed, using a slightly modified model taken from the literature. Parameter values reported here are generally consistent with those obtained by the original model. Caffeine (0.5 mmol.l-1) moderately enhanced the overall myoplasmic calcium removal. In particular, the rate constant of the non-saturable uptake increased by 51% on the average, but there was a considerable fiber-to-fiber variation. The kinetic features of the binding sites representing the saturable uptake did not change significantly while the concentration of the available sites decreased by 36%. It is concluded that the caffeine-induced changes of the calcium removal components can be explained by supposing an increased resting myoplasmatic Ca2+ concentration in the presence of the drug.