THE PHARMACOLOGY OF INTRACELLULAR CA2-RELEASE CHANNELS()

Two classes of intracellular Ca2+-release channels, the ryanodine rece ptor and the inositol (1,4,5)-trisphosphate (IP3) receptor, are essent ial for spatio-temporal Ca2+ signalling in cells. Heparin and caffeine have been widely used to study these channels. It was originally thou ght that caffeine acts solely as an agonist for the ryanodine receptor and heparin acts solely as an inhibitor for the IP3 receptor. However , recent experiments indicate that these compounds have multiple effec ts, and are discussed in this review by Barbara Ehrlich and colleagues . In the same concentration range, caffeine activates the ryanodine re ceptor and inhibits the IP3 receptor, and heparin inhibits the IP3 rec eptor and activates the ryanodine receptor. More specific pharmacologi cal tools that are suitable for studies of ryanodine and IP3 receptors are now beginning to emerge.