R- and L-type Ca2+ channels are insensitive to eliprodil in rat cultured cerebellar granule neurons

We have investigated, by using the whole-cell patch-clamp technique, the Ca2+ channel antagonist properties of eliprodil in cultured cerebellar granule cells which are known to express L-, N-, P- as well as Q- and R-type Ca2+ channels. Eliprodil maximally antagonized 50% of the voltage-dependent Ba2+ current with an IC50 of 4 mu M. omega-Conotoxin-GVIA (3.2 mu M) and omega-agatoxin-IVA (0.5 mu M) blocked 28 and 43% of the current, respectively. When eliprodil (30 mu M) was added to omega-conotoxin-GVLA or omega-agatoxin-IVA the magnitude of the maximal inhibition was identical to that obtained with eliprodil alone confirming a full blockade by eliprodil of N-, P- and Q-type Ca2+ channels. The L-type channel antagonist nimodipine (10 mu M) blocked 24% of the current; this blockade was fully additive to that of eliprodil, indicating that the nimodipine-sensitive component of the current is eliprodil-insensitive. In the presence of eliprodil and nimodipine a residual Cd2+ sensitive current (25%), identified as the R-type current. remained unblocked. We conclude that in cerebellar granule neurons R- and L-type Ca2+ channels are insensitive to eliprodil. The nimodipine- sensitive channels present in cerebellar granule neurons may represent a neuronal subtype of L channels distinct from that (eliprodil-sensitive/nimodipine-sensitive) present in cortical or hippocampal neurons.