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

Abstract

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