Control of IsAHP in mouse hippocampus CA1 pyramidal neurons by RyR3-mediated calcium-induced calcium release.

In several neuronal preparations, the ryanodine-sensitive calcium store was reported to participate in the generation of slow afterhyperpolarization currents (IsAHP) involved in spike frequency adaptation. We show that calcium release from the ryanodine-sensitive calcium store is a major determinant of the triggering of IsAHP in mouse CA1 pyramidal neurons. Whole-cell patch clamp recordings in hippocampus slices show that the intracellular calcium stores depletion using an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase (5 muM cyclopiazonic acid), as well as the specific blockade of ryanodine receptors (100 muM ryanodine) both reduced the IsAHP by about 70%. Immunohistology, using an anti-RyR3 specific antibody, indicates that RyR3 expression is particularly enriched in the CA1 apical dendrites (considered as the most important site for sAHP generation). We show that our anti-RyR3 antibody acts as a functional RyR3 antagonist and induced a reduction in IsAHP by about 70%. The additional ryanodine application (100 mu M) did not further affect IsAHP, thus excluding RyR2 in IsAHP activation. Our results argue in favor of a specialized function of RyR3 in CA1 pyramidal cells in triggering IsAHP due to their localization in the apical dendrite.