Ryanodine receptor adaptation: control mechanism of Ca(2+)-induced Ca2+ release in heart.

Adaptation of single cardiac ryanodine receptor (RyR) channels was demonstrated by application of the caged calcium ion (Ca2+) methodology. In contrast to conventional desensitization found in surface membrane ligand-gated channels, single cardiac RyR channels adapted to maintained Ca2+ stimuli, preserving their ability to respond to a second (larger) Ca2+ stimulus. RyR adaptation may represent a molecular control mechanism for smoothly graded Ca(2+)-induced Ca2+ release in heart and may be a fundamental feature of channels, including the inositol triphosphate receptor, that are involved in intracellular Ca2+ signaling in many cell types.