Local oscillations of frog skeletal muscle sarcomeres induced by subthreshold concentration of caffeine.

Different intracellular processes are selectively controlled by a signalling system based on transient rises or oscillations of cytoplasmic calcium concentration, which transmit extracellular signals at subcellular level. When treated with a subthreshold concentration of caffeine, skeletal muscle cells provide a suitable preparation to study mechanisms which generate repetitive calcium transients. Based on optical diffraction measurements of local contractions of individual sarcomeres, we have shown substantial enhancement of spontaneous repetitive calcium release in the presence of subthreshold caffeine concentration. Calcium release propagates to neighbor calcium sources and forms slow contraction waves. A power spectra density analysis has revealed parameters of the time course of these events. However, substantial amounts of calcium released in sarcomeres are not synchronized.