Involvement of ryanodine receptors in spc-induced calcium release from brain microsomes.

Sphingosylphosphorylcholine (SPC) releases Ca2+ from brain microsomes. SPC-induced CA2+ release differs from IP3-induced Ca2+ release in that it is more extensive in the cerebrum than in the cerebellum. SPC has little effect on [3H] IP3 binding but enhances [3H] ryanodine binding, as expected for an activator of ryanodine receptors. SPC-induced Ca2+ release is inhibited by ryanodine receptor blockers but not by selective blockers of IP3 receptors. We conclude that SPC releases Ca2+ from brain microsomes by activating ryanodine receptors rather than IP3 receptors. Activation of an additional SPC-sensitive pathway for releasing Ca2+ is not precluded.