DEVELOPMENTAL-CHANGES IN PRESYNAPTIC CALCIUM CHANNELS COUPLED TO GLUTAMATE RELEASE IN CULTURED RAT HIPPOCAMPAL-NEURONS

Excitatory synaptic transmission in the hippocampus involves the parti cipation of at least two types of presynaptic Ca2+ channels, N-type ch annels sensitive to omega-conotoxin GVIA (omega-CTx GVIA) and Q-type c hannels sensitive to omega-agatoxin IVA (omega-Aga IVA), Hippocampal p yramidal neurons in cell culture were used to examine the participatio n of these two classes of channels at different stages of synapse deve lopment, Specific Ca2+ channel toxins were used to block presynaptic C a2+ channels while whole-cell voltage-clamp recordings were used to re cord evoked EPSCs in postsynaptic neurons, At immature synapses (cells in culture for 10-15 d), omega-CTx GVIA (1-5 mu M) blocked transmissi on by more than 80% while omega-Aga IVA(1 mu M) was less effective, In older cultures, however, omega-Aga IVA (1 mu M) was more effective th an omega-CTx GVIA (1-5 mu M) in blocking synaptic transmission, The ph armacological properties of the omega-Aga IVA sensitive component of s ynaptic transmission were examined in more detail using omega-Aga IVA and omega-conotoxin MVIIC (omega-CTx MVIIC), The properties of this co mponent of transmitter release indicated that a Q-type Ca2+ channel wa s involved in presynaptic Ca2+ entry, The results suggest that differe nt classes of presynaptic Ca2+ channels begin to participate in transm itter release at different times during synapse development and matura tion.