High voltage-activated Ca2+ channel currents in isolectin B4-positive and -negative small dorsal root ganglion neurons of rats

Voltage-gated Ca2+ channels in the primary sensory neurons are important for neurotransmitter release and regulation of nociceptive transmission. Although multiple classes of Ca2+ channels are expressed in the dorsal root ganglion (DRG) neurons, little is known about the difference in the specific channel subtypes among the different types of DRG neurons. In this study, we determined the possible difference in high voltage- activated Ca2+ channel currents between isolectin B-4 (IB4)-Positive and IB4-negative small-sized (15-30 mum) DRG neurons. Rat DRG neurons were acutely isolated and labeled with IB4 conjugated to a fluorescent dye. Whole-cell patch clamp recordings of barium currents flowing through calcium channels were performed on neurons with and without IB4. The peak current density of voltage-gated Ca2+ currents was not significantly different between IB4-positive and IB4-negative neurons. Also, both nimodipine and W-agatoxin IVA produced similar inhibitory effects on Ca2+ currents in these two types of neurons. However, block of N-type Ca2+ channels with omega-conotoxin GVIA produced a significantly greater reduction of Ca2+ currents in IB4-positive than IB4-negative neurons. Furthermore, the IB4-positive neurons had a significantly smaller residual Ca2+ currents than IB4-negative neurons. These data suggest that a higher density of N-type Ca2+ channels is present in IB4-positive than IB4-negative small-sized DRG neurons. This differential expression of the subtypes of high voltage-activated Ca2+ channels may contribute to the different function of these two classes of nociceptive neurons. (C) 2004 Elsevier Ireland Ltd. All rights reserved.