Multiple Ca2+ currents elicited by action potential waveforms in acutely isolated adult rat dorsal root ganglion neurons.

Ca2+ entry into different diameter cell bodies of dorsal root ganglion (DRG) neurons depolarized with action potential (AP) waveform commands was studied using the whole-cell patch-clamp technique and pharmacological probes. We have previously shown that Ca2+ current expression in DRG neuron cell bodies depends on cell diameter. In small diameter DRG neurons, L- and N-type Ca2+ currents usually accounted for most Ca2+ entry during APs as determined by blockade with nimodipine and omega-conotoxin GVIA (omega-CgTx). In medium- diameter DRG neurons, T-type Ca2+ currents accounted for 29% or 54% of Ca2+ entry in cells held at -60 mV or -80 mV, respectively, based on blockade by amiloride. T-type Ca2+ currents did not usually contribute to Ca2+ entry in large diameter DRG neurons. An amiloride/omega-CgTx/nimodipine-resistant Ca2+ current was prominent in medium diameter DRG neurons, while L- and N-type Ca2+ currents played a relatively small role in Ca2+ entry. In all DRG neuron sizes, AP-generated currents were large in amplitude, resulting in significant Ca2+ entry. APs with slower rates of repolarization increased Ca2+ entry. In DRG neurons that expressed T-type Ca2+ currents, the duration of Ca2+ current entry during APs was prolonged, and this prolongation was reduced by amiloride. Thus, antagonists selective for different Ca2+ channels produced different patterns of blockade of AP-generated Ca2+ entry in different diameter DRG cell bodies. Selective Ca2+ channel modulation by neurotransmitters might be expected to have similar effects.