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

R-type Ca(v)2.3 high voltage-activated Ca2+ channels in peripheral sensory neurons contribute to pain transmission. Recently we have demonstrated that, among the six Ca(v)2.3 isoforms (Ca(v)2.3a similar to Ca(v)2.3e), the Ca(v)2.3e isoform is primarily expressed in trigeminal ganglion (TG) nociceptive neurons. In the present study, we further investigated expression patterns of Ca(v)2.3 isoforms in the dorsal root ganglion (DRG) neurons. As in TG neurons, whole tissue RT-PCR analyses revealed the presence of two isoforms, Ca(v)2.3a and Ca(v)2.3e, in DRG neurons. Single-cell RT-PCR detected the expression of Ca(v)2.3e mRNA in 20% (n=14/70) of DRG neurons, relative to Ca(v)2.3a expression in 2.8% (n=2/70) of DRG neurons. Ca(v)2.3e 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(v)2.3e in nociceptive DRG neurons. Moreover, Ca(v)2.3e was preferentially expressed in tyrosine-kinase A (trkA)-positive, iso-lectin B4 (IB4)-negative and transient receptor potential vanilloid 1 (TRPV1)-positive neurons. These results suggest that Ca(v)2.3e 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 trigerninal system but also in the spinal system.