CAFFEINE-INDUCED RELEASE OF INTRACELLULAR CA2-HAMSTER OVARY CELLS EXPRESSING SKELETAL-MUSCLE RYANODINE RECEPTOR - EFFECTS ON FULL-LENGTH AND CARBOXYL-TERMINAL PORTION OF CA2+ RELEASE CHANNELS( FROM CHINESE)

The ryanodine receptor (RyR)/Ca2+ release channel is an essential comp onent of excitation-contraction coupling in striated muscle cells. To study the function and regulation of the Ca2+ release channel, we test ed the effect of caffeine on the full-length and carboxyl-terminal por tion 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 carbo xyl-terminal RyR channels. CHO cells expressing the carboxyl-terminal RyR proteins displayed spontaneous changes of intracellular [Ca2+]. Un like the native RyR channels in muscle cells, which display localized Ca2+ release events (i.e., ''Ca2+ sparks'' in cardiac muscle and ''loc al release events'' in skeletal muscle), CHO cells expressing the full length RyR proteins did not exhibit detectable spontaneous or caffein e-induced local Ca2+ release events, Our data suggest that the binding site for caffeine is likely to reside within the amino-terminal porti on of RyR, and the localized Ca2+ release events observed in muscle ce lls may involve gating of a group of Ca2+ release channels and/or inte raction of RyR with muscle-specific proteins.