Classification of voltage-dependent Ca2+ channels in trigeminal ganglion neurons from neonatal rats

We examined the subtypes and characteristics of the Ca2+ channel in small (diameter < 30 mum) trigeminal ganglion (TG) neurons from neonatal rats by means of whole cell patch clamp techniques. There were two current components, low-voltage activated (LVA) and high-voltage activated (HVA) I-Ba, with different activation ranges and waveforms. LVA I-Ba elicited from a depolarizing step pulse at a holding potential (HP) of - 80 mV was inhibited by 0.25 mM amiloride (62%), which did not produce any significant inhibition of the peak amplitude of HVA I-Ba. The application of 0.5 mM amiloride inhibited 10% of the HVA I-Ba. The LVA I-Ba was also reduced by changing the HP from - 80 to - 60 mV (61%), and under these conditions the peak amplitude of HVA I-Ba did not change significantly. In addition, HVA I-Ba and LVA I-Ba showed marked differences in their inactivation properties. Experiments with several Ca2+ channel blockers revealed that on average, 26% of the HVA I-Ba was nifedipine (10 muM) sensitive, 55%,was sensitive to omega-conotoxinGVIA (1 muM), 4% was blocked by omega-agatoxinIVA (1 muM), and the remainder of the current that was resistant to the co-application of all three Ca2+ channel blockers was 15% of the total current. These results suggest that the application of amiloride and the alteration of the holding potential level can discriminate between HVA and LVA Ba2+ currents in TG neurons, and that TG neurons expressed T-, L-, N-, P-/Q- and R-type Ca2+ channels. (C) 2003 Elsevier Science Inc. All rights reserved.