Korean J Physiol Pharmacol.  2010 Feb;14(1):45-49. 10.4196/kjpp.2010.14.1.45.

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

Affiliations
  • 1National Research Laboratory for Pain, Dental Research Institute and Department of Physiology School of Dentistry, Seoul National University, Seoul 110-749, Korea. odolbae@snu.ac.kr
  • 2Department of Physiology, College of Medicine, Kangwon National University, Chunchon 200-710, Korea.

Abstract

R-type Cav2.3 high voltage-activated Ca2+ channels in peripheral sensory neurons contribute to pain transmission. Recently we have demonstrated that, among the six Cav2.3 isoforms (Cav2.3a~Cav2.3e), the Cav2.3e isoform is primarily expressed in trigeminal ganglion (TG) nociceptive neurons. In the present study, we further investigated expression patterns of Cav2.3 isoforms in the dorsal root ganglion (DRG) neurons. As in TG neurons, whole tissue RT-PCR analyses revealed the presence of two isoforms, Cav2.3a and Cav2.3e, in DRG neurons. Single-cell RT-PCR detected the expression of Cav2.3e mRNA in 20% (n=14/70) of DRG neurons, relative to Cav2.3a expression in 2.8% (n=2/70) of DRG neurons. Cav2.3e 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 Cav2.3e in nociceptive DRG neurons. Moreover, Cav2.3e was preferentially expressed in tyrosine-kinase A (trkA)-positive, isolectin B4 (IB4)-negative and transient receptor potential vanilloid 1 (TRPV1)-positive neurons. These results suggest that Cav2.3e 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.

Keyword

R-type calcium channels; Cav2.3; Voltage-activated calcium channels; DRG neurons

MeSH Terms

Animals
Calcium Channels, R-Type
Diagnosis-Related Groups
Ganglia, Spinal
Lectins
Neurons
Nociceptors
Protein Isoforms
Rats
RNA, Messenger
Sensory Receptor Cells
Spinal Nerve Roots
Trigeminal Ganglion
Calcium Channels, R-Type
Lectins
Protein Isoforms
RNA, Messenger

Figure

  • Fig. 1. (A) Schematic diagram of α1E (Cav2.3) subunit. The structural variations cover two segments of 19 (insert I) and 7 amino acids (insert II) in the loop between domain II and III, and a third segment of 43 amino acids (insert III) in the proximal carboxy terminus. (B) Two Cav2.3 isoforms were found in DRG. Insert I, II and III was analyzed by whole tissue RT-PCR. Cav2.3 isoforms amplified from DRG neurons have insert II, but not insert I, and either lack or contain insert III depending on the isoform. Cav2.3a contains insert II, but not insert I and insert III, while Cav2.3e has insert II and insert III, but not insert I. (C) Illustrated are the locations of the primers designed to detect insert I, insert II and insert III for RT-PCR analysis in relation to the Cav2.3 subunit.

  • Fig. 2. Expression of Cav2.3a and Cav2.3e isoforms from individual DRG neurons. (A) Single-cell RT-PCR products amplified with nested primer from DRG neurons. PCR products, with or without insert III (larger, 1 and smaller, 2), were produced in each DRG neuron. (B) Representative gels showing single-cell RT-PCR products amplified using insert III-specific primers. The numbers (1–5) indicate five different neurons examined from single-cell RT-PCR reaction. β-actin was used in each reaction as a positive control. Circle diagram shows the distribution of Cav2.3a and Cav2.3e in DRG neurons (total 70 neurons).

  • Fig. 3. Expression pattern of Cav2.3e was analyzed in three groups: small-sized (<16μm), medium-sized (16∼20 μm) and large-sized (20∼30 μm) DRG neurons. Representative gels showing single-cell RT-PCR products obtained from six different neurons. White bars indicate the number of neurons in each group; black bars indicate the number of neurons with expression of Cav2.3e.

  • Fig. 4. (A) Small-sized DRG neurons were divided into IB4-negative and IB4-positive neurons; expression of Cav2.3e was determined in each group with or without trkA and P2X3 expression. The black bar in the graph shows that Cav2.3e is prominent in trkA+/IB4-/TRPV1+ neurons. (B) Expression of Cav2.3e in TRPV1-expressing nociceptive neurons. Representative gels showing RT-PCR products amplified with Cav2.3e, TRPV1, and β-actin-specific primers from six different neurons. The majority of small-sized Cav2.3e-expressing DRG neurons are also TRPV1-positive, though TRPV1 expression is not exclusive to DRG expressing the Cav2.3e subunit (graph; right).


Reference

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