Caffeine-induced Release of Intracellular Ca(2+) from Chinese Hamster Ovary Cells Expressing Skeletal Muscle Ryanodine Receptor : Effects on Full-Length and Carboxyl-Terminal Portion of Ca(2+)Release Channels

The ryanodine receptor (RyR)/Ca(2+) release channel is an essential component of excitation–contraction coupling in striated muscle cells. To study the function and regulation of the Ca(2+) release channel, we tested the effect of caffeine on the full-length and carboxyl-terminal portion of skeletal muscle RyR expressed in a Chinese hamster ovary (CHO) cell line. Caffeine induced openings of the full length RyR channels in a concentration-dependent manner, but it had no effect on the carboxyl-terminal RyR channels. CHO cells expressing the carboxyl-terminal RyR proteins displayed spontaneous changes of intracellular [Ca(2+)]. Unlike the native RyR channels in muscle cells, which display localized Ca(2+) release events (i.e., “Ca(2+) sparks” in cardiac muscle and “local release events” in skeletal muscle), CHO cells expressing the full length RyR proteins did not exhibit detectable spontaneous or caffeine-induced local Ca(2+) release events. Our data suggest that the binding site for caffeine is likely to reside within the amino-terminal portion of RyR, and the localized Ca(2+) release events observed in muscle cells may involve gating of a group of Ca(2+) release channels and/or interaction of RyR with muscle-specific proteins.