Classification of voltage-dependent Ca 2+ channels in trigeminal ganglion neurons from neonatal rats

Abstract

We examined the subtypes and characteristics of the Ca 2+ channel in small (diameter < 30 μm) 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 Ca 2+ channel blockers revealed that on average, 26% of the HVA I Ba was nifedipine (10 μM) sensitive, 55% was sensitive to ω-conotoxinGVIA (1 μM), 4% was blocked by ω-agatoxinIVA (1 μM), and the remainder of the current that was resistant to the co-application of all three Ca 2+ 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 Ba 2+ currents in TG neurons, and that TG neurons expressed T-, L-, N-, P-/Q- and R-type Ca 2+ channels.