Calcium channel subtypes on glutamatergic mossy fiber terminals synapsing onto rat hippocampal CA3 neurons

The current electrophysiological study investigated the functional roles of high- and low-voltage-activated calcium (Ca2+) channel subtypes on glutamatergic small mossy fiber nerve terminals (SMFTs) that synapse onto rat hippocampal CA3 neurons. Experiments combining both the 'synapse bouton' preparation and single-pulse focal stimulation technique were performed using the conventional whole-cell patch configuration under voltage-clamp conditions. Nifedipine, at a high concentration, and BAY-K8644 (BAY-K) inhibited and facilitated the glutamatergic excitatory postsynaptic currents (eEPSCs) that were evoked by 0.2-Hz stimulation, respectively. However, these drugs had no effects on spontaneous EPSCs (sEPSCs). Following the use of a high stimulation frequency of 3 Hz, however, nifedipine markedly inhibited eEPSCs at the low concentration of 0.3 µM. Moreover, ω-conotoxin GVIA (ω-CgTXGVIA) and ω-agatoxin IVA (ω-AgTXIVA) significantly inhibited both sEPSCs and eEPSCs. Furthermore, SNX-482 slightly inhibited eE...