LACTOSERIES CARBOHYDRATE ANTIGEN, GAL-BETA-1-4GLCNAC-R, IS EXPRESSED BY A SUBPOPULATION OF CAPSAICIN-SENSITIVE RAT SENSORY NEURONS

1. The membrane properties of dorsal root ganglion (DRG) cells express ing the lactoseries carbohydrate antigen Gal beta 1-4GlcNAc-R were stu died and compared with those of DRG cells lacking this antigen. Acutel y dissociated rat DRG cells that ex pressed Gal beta 1-4GlcNAc-R on th eir outer cell membranes were detected with the use of a primary monoc lonal 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 mu g/ml of A5 to be a saturating concentrat ion of primary antibody that labeled similar to 19% of the DRG cells. A battery of membrane properties including action potential (AP) durat ion; sensitivity to capsaicin; expression of H current (I-H). A curren t (I-A), and Ca2+ current subtypes (L, N, and T); and inhibition of hi gh-threshold Ca2+ currents by serotonin (5HT) or 8-hydroxy-2-(di-N-pro pylamino)-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(+) ce lls tested, 33 were sensitive to 1 mu M capsaicin, which produced an i nward current averaging 4 +/- 0.46 (SE) nA (n = 33). In contrast, only 12 of 33 A5(-) cells were sensitive to 1 mu M capsaicin, which produc ed 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 I-H and I-A A5(+) cells had significantly larg er N-type Ca2+ currents and expressed I-A more frequently than A5(-) c ells. Conversely, A5(-) cells had significantly longer AP duration and larger T-type Ca2+ currents, and expressed I-H more frequently compar ed with A5(+) cells. 4. A5(+) and A5(-) cells differed regarding the i nhibition of high-threshold Ca2+ currents by maximal concentrations of 5HT(1A) agonists (10 mu M 5HT or 1 mu M 8-OH-DPAT). Inhibition of Ca2 + currents in A5(+) cells by 1 mu M 8-OH-DPAT (n = 15) or 10 mu M 5HT (n = 18) averaged 4 +/- 0.9%. In contrast, inhibition of Ca2+ currents in A5(-) cells by 10 mu M 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 I -H, I-A, and T-type Ca2+ current amplitude, and the distribution of A5 (+) and A5(-) cells among the various groups was observed. The categor ies were defined as follows: type 1 (capsaicin sensitive, no I-H or I- A); type 2 (capsaicin sensitive, significant I-A); type 3 (capsaicin i nsensitive, T-type Ca2+ currents <1 nA, significant I-H but no I-A); a nd type 4 (capsaicin insensitive, T-type Ca2+ currents >2.4 nA). On th e 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 t ype 1 category (A5(+), n = 6 and A5(-), n = 9). These two groups varie d regarding the sensitivity of Ca2+ currents to maximally effective co ncentrations of 5HT(1A) agonists. In type 1 A5(+) DRG cells, high-thre shold Ca2+ currents were not significantly inhibited by 1 mu M 8-OH-DP AT (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 mu M 5HT. 7. The several significant differences in membrane pr operties between A5(-) and A5(+) DRG cells suggest that the Gal beta 1 -4GlcNAc-R antigen is expressed by a distinct subset of DRG cells, con sisting predominately of type 1 and type 2 cells. The observation that most A5(+) DRG cells were capsaicin sensitive suggests that the Gal b eta 1-4GlcNAc-R antigen is expressed primarily by nociceptors. This id ea is consistent with a previous study in which investigators observed the Gal beta 1-4GlcNAc-R antigen on a subpopulation of DRG neurons wi th afferent terminals in lamina I and II of the spinal cord, an import ant relay area for nociceptive information.