The Cav2.3 Ca2+ channel subunit contributes to R-type Ca2+ currents in murine hippocampal and neocortical neurones

Different subtypes of voltage-dependent Ca2+ currents in native neurones are essential in coupling action potential firing to Ca2+ influx. For most of these currents, the underlying Ca2+ channel subunits have been identified on the basis of pharmacological and biophysical similarities. In contrast, the molecular basis of R-type Ca2+ currents remains controversial. We have therefore examined the contribution of the Ca(v)2.3 (alpha(1E)) subunits to R-type currents in different types of central neurones using wild-type mice and mice in which the Cav2.3 subunit gene was deleted. In hippocampal CA1 pyramidal cells and dentate granule neurones, as well as neocortical neurones of wild-type mice, Ca2+ current components resistant to the combined application of omega-conotoxin GVIA and MVIIC, omega-agatoxin IVa and nifedipine (I-Ca,I-R) were detected that were composed of a large R-type and a smaller T-type component. In Ca(v)2.3-deficient mice, I-Ca,I-R was considerably reduced in CA1 neurones (79%) and cortical neurones (87%), with less reduction occurring in dentate granule neurones (47%). Analysis of tail currents revealed that the reduction Of I-Ca,I-R is due to a selective reduction of the rapidly deactivating R-type current component in CA1 and cortical neurones. In all cell types, I-Ca,I-R was highly sensitive to Ni2+ (100 muM: 71-86% block). A selective antagonist of cloned Ca(v)2.3 channels, the spider toxin SNX-482, partially inhibited I-Ca,I-R at concentrations up to 300 nm in dentate granule cells and cortical neurones (50 and 57% block, EC50 30 and 47 nm, respectively) I-Ca,I-R in CA1 neurones was significantly less sensitive to SNX-482 (27% block, 300 nm SNX-482). Taken together, our results show clearly that Cav2.3 subunits underlie a significant fraction Of ICa,R in different types of central neurones. They also indicate that Ca(v)2.3 subunits may give rise to Ca2+ currents with differing pharmacological properties in native neurones.