R-type Calcium Channel Isoform in Rat Dorsal Root Ganglion Neurons

R-type Calcium Channel Isoform in Rat Dorsal Root Ganglion Neurons

R-type Ca_v2.3 high voltage-activated Ca²⁺ channels in peripheral sensory neurons contribute to pain transmission. Recently we have demonstrated that, among the six Ca_v2.3 isoforms (Ca_v2.3a∼Ca_v2.3e), the Ca_v2.3e isoform is primarily expressed in trigeminal ganglion (TG) nociceptive neurons. In the present study, we further investigated expression patterns of Ca_v2.3 isoforms in the dorsal root ganglion (DRG) neurons. As in TG neurons, whole tissue RT-PCR analyses revealed the presence of two isoforms, Ca_v2.3a and Ca_v2.3e, in DRG neurons. Single-cell RT-PCR detected the expression of Ca_v2.3e mRNA in 20% (n=14/70) of DRG neurons, relative to Ca_v2.3a expression in 2.8% (n=2/70) of DRG neurons. Ca_v2.3e mRNA was mainly detected in small-sized neurons (n=12/14), but in only a few medium-sized neurons (n=2/14) and not in large-sized neurons, indicating the prominence of Ca_v2.3e in nociceptive DRG neurons. Moreover, Ca_v2.3e was preferentially expressed in tyrosine-kinase A (trkA)-positive, iso</SUB>lectin B4 (IB4)-negative and transient receptor potential vanilloid 1 (TRPV1)-positive neurons. These results suggest that Ca_v2.3e may be the main R-type Ca²⁺ channel isoform in nociceptive DRG neurons and thereby a potential target for pain treatment, not only in the trigeminal system but also in the spinal system.