INVOLVEMENT OF RYANODINE RECEPTORS IN SPHINGOSYLPHOSPHORYLCHOLINE-INDUCED CALCIUM-RELEASE FROM BRAIN MICROSOMES

Sphingosylphosphorylcholine (SPC) releases Ca2+ from brain microsomes. SPC-induced Ca2+ release differs from IP3-induced Ca2+ release in tha t it is more extensive in the cerebrum than in the cerebellum. SPC has little effect on [H-3] IP3 binding but enhances [H-3] ryanodine bindi ng, as expected for an activator of ryanodine receptors. SPC-induced C a2+ release is inhibited by ryanodine receptor blockers but not by sel ective blockers of IP3 receptors. We conclude that SPC releases Ca2+ f rom brain microsomes by activating ryanodine receptors rather than IP3 receptors. Activation of an additional SPC-sensitive pathway for rele asing Ca2+ is not precluded.