Multiple subtypes of voltage-gated calcium currents in the Edinger-Westphal nucleus

Abstract

Avian Edinger-Westphal (EW) neurons provide a unique opportunity to compare electrophysiologically the membranes of cell bodies and terminals in the same population of neurons. Axons that originate from neurons in the lateral region of the EW nucleus form a morphologically distinct presynaptic terminal, known as a calyx, on ciliary ganglion neurons [32]. Several studies have shown that calyciform terminals in the ciliary ganglion exhibit predominantly N-type, high-voltage-activated (HVA) calcium channels [35–37,45]. The goal of this study was to characterize and compare the calcium currents expressed in EW cell somas with those reported in the terminals. Whole-cell patch-clamp techniques were used to record from cell bodies in the lateral EW nucleus in slice preparations. Slices were obtained from embryonic day 16 chicks, matching the age of the embryos in which calyces were studied. Recordings were localized to the lateral region of the EW nucleus using Lucifer yellow fills. Voltage-step commands from −70 to 0 mV produced calcium currents with both a sustained and an inactivating component. Depolarization steps to 0 mV from a holding potential of −40 mV eliminated the inactivating component. These recordings suggested the presence of both LVA and HVA calcium currents.Application of 0.1 mM NiCl2 produced a reversible decrease in the amplitude of the whole-cell calcium current, preferentially affecting the inactivating component. The Ni2+ -sensitive current activated and inactivated rapidly in a voltage-dependent manner. Treatment with 0.1 mM cadmium chloride caused a reversible reduction in the amplitude of the calcium current. ω-Conotoxin (CTX) (0.002 mM) produced an irreversible decrease in the amplitude of the calcium current. An unidentified component of the calcium current, which was Ni2+- and CTX-insenive, constituted ≈10–15% of the current. Nifedipine (0.010 mM) had no detectable effects on the calcium currents. These results suggest that, in contrast to their terminals, cell bodies in the lateral region of the EW nucleus express T-type, LVA as well as N-type, HVA calcium channels.