Journal of Neurophysiology, Vol 76, Issue 4 2192-2199, Copyright © 1996 by APS

ARTICLES

Lactoseries carbohydrate antigen, Gal beta 1-4GlcNAc-R, is expressed by a subpopulation of capsaicin-sensitive rat sensory neurons

L. P. Del Mar and R. S. Scroggs
University of Tennessee College of Medicine, Department of Anatomy and Neurobiology, Memphis 38163, USA.

1. The membrane properties of dorsal root ganglion (DRG) cells expressing the lactoseries carbohydrate antigen Gal beta 1-4GlcNAc-R were studied and compared with those of DRG cells lacking this antigen. Acutely dissociated rat DRG cells that expressed Gal beta 1-4GlcNAc-R on their outer cell membranes were detected with the use of a primary monoclonal mouse IgM antibody (A5), directed against Gal beta 1-4GlcNAc-R, and a fluorescent secondary antibody (fluorescein-conjugated goat anti-mouse IgM). We found 12.8 micrograms/ml of A5 to be a saturating concentration of primary antibody that labeled approximately 19% of the DRG cells. A battery of membrane properties including action potential (AP) duration; sensitivity to capsaicin; expression of H current (IH), A current (IA), and Ca2+ current subtypes (L, N, and T); and inhibition of high-threshold Ca2+ currents by serotonin (5HT) or 8-hydroxy-2-(di-N-propylamino)-tetralin (8-OH-DPAT) was measured in DRG cells labeled (A5+) and unlabeled (A5-) by a saturating concentration of A5. 2. There was a significant difference in the number of capsaicin-sensitive DRG cells and a significant difference in the magnitude of the capsaicin-induced inward current in A5+ versus A5- DRG cells. Of 35 A5+ cells tested, 33 were sensitive to 1 microM capsaicin, which produced an inward current averaging 4 +/- 0.46 (SE) nA (n = 33). In contrast, only 12 of 33 A5- cells were sensitive to 1 microM capsaicin, which produced an inward current averaging 1.2 +/- 0.52 nA (n = 12). 3. There were also significant differences between A5+ and A5- cells regarding average AP duration, N- and T-type Ca2+ current amplitude, and number of cells that expressed IH and IA. A5+ cells had significantly larger N-type Ca2+ currents and expressed IA more frequently than A5- cells. Conversely, A5- cells had significantly longer AP duration and larger T-type Ca2+ currents, and expressed IH more frequently compared with A5+ cells. 4. A5+ and A5- cells differed regarding the inhibition of high-threshold Ca2+ currents by maximal concentrations of 5HT1A agonists (10 microM 5HT or 1 microM 8-OH-DPAT). Inhibition of Ca2+ currents in A5+ cells by 1 microM 8-OH-DPAT (n = 15) or 10 microM 5HT (n = 18) averaged 4 +/- 0.9%. In contrast, inhibition of Ca2+ currents in A5- cells by 10 microM 5HT (n = 33) averaged 20 +/- 3.8%. 5. Cells for which sufficient data were collected were categorized as type 1, 2, 3, or 4 on the basis of sensitivity to capsaicin and expression of IH, IA, and T-type Ca2+ current amplitude, and the distribution of A5+ and A5- cells among the various groups was observed. The categories were defined as follows: type 1 (capsaicin sensitive, no IH or IA); type 2 (capsaicin sensitive, significant IA); type 3 (capsaicin insensitive, T-type Ca2+ currents < 1 nA, significant IH but no IA); and type 4 (capsaicin insensitive, T-type Ca2+ currents > 2.4 nA). On the basis of this criteria, 6 of 15 type 1 cells and all type 2 cells (n = 19) were A5+. All type 3 cells (n = 8) and all type 4 cells (n = 11) were A5-. 6. As indicated above, the expression of the Gal beta 1-4GlcNAc-R antigen differentiated two subgroups of DRG cells in the type 1 category (A5+, n = 6 and A5-, n = 9). These two groups varied regarding the sensitivity of Ca2+ currents to maximally effective concentrations of 5HTIA agonists. In type 1 A5+ DRG cells, high-threshold Ca2+ currents were not significantly inhibited by 1 microM 8-OH-DPAT (average inhibition = 1.2 +/- 0.8%, n = 6). However, in type 1 A5- cells, high-threshold Ca2+ currents were reduced 47 +/- 6.0% (n = 9) by 10 microM 5HT. 7. The several significant differences in membrane properties between A5+ and A5- DRG cells suggest that the Gal beta 1-4GlcNAc-R antigen is expressed by a distinct subset of DRG cells, consisting predominately of type 1 and type 2 cells. The observation that most A5+ DRG cells were capsaicin sensitive suggests that the Gal beta 1-4GlcNAc-R antigen is expressed primarily by n

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