Calcium and strontium concentration changes within skinned muscle preparations following a change in the external bathing solution.

Abstract

A method for producing rapid [Ca2+] and [Sr2+] changes in the frog skinned muscle fiber preparation while maintaining constant all other cationic concentrations was described and analyzed in detail. Different experiments, some of them involving the Ca2+-sensitive photoprotein aequorin and theoretical considerations, indicated that with this method a Ca2+ (or Sr2+) concentration change was produced within 0.1-0.15 s in a whole preparation having a diameter of 50 .mu.m. Rate of force development was similar to that observed in vivo. The radial diffusion coefficient of EGTA [ethylene glycol bis (.beta.-aminoethyl ether) N,N,N'',N''-tetraacetic acid] in relaxed myofibrillar preparations apparently was 4.6 .times. 10-6 cm2 s-1 at 20.degree. C. The sarcoplasmic reticulum in myofibrillar bundles was active with respect to Ca2+ and Sr2+ in solutions used ([Mg2+] 1 mM; [Na] 30 mM; [K] 140-170 mM; [Cl] .ltoreq. 20 mM; pH 7.10). Amount of Ca released by caffeine from internal stores (previously loaded with Ca) raised total Ca concentration in the muscle fiber preparation by at least 1.8 mM. The presence of 10 mM-caffeine in all bathing solutions drastically reduced the ability of the sarcoplasmic reticulum to accumulate Ca and Sr.