RAT DORSAL-ROOT GANGLION NEURONS EXPRESS DIFFERENT CAPSAICIN-EVOKED CA2+ TRANSIENTS AND PERMEABILITIES TO MN2+

Capsaicin (1 mu M) evoked [Ca2+](i) transients in two-thirds of a Perc oll-gradient enriched population of rat dorsal root ganglion (DRG) neu rones. Amongst the capsaicin-sensitive neurones, 68% responded to caps aicin with peak [Ca2+](i) transients of 681 +/- 67 nM, whereas the rem aining neurones gave peak [Ca2+](i) transients of 260 +/- 84 nM. In th e presence of Mn2+ in Ca2+-free medium, capsaicin evoked quenching of fura-2 fluorescence, due to Mn2+ influx, in a similar proportion of ne urones. Two patterns of capsaicin-sensitive Mn2+ quenching were observ ed: 72% of neurones showed rapid quenching (t(1/2) of 18.3 +/- 4.1 s), whereas the remaining neurones had low quenching rates (t(1/2) of 119 +/- 33 s). Distinct capsaicin-sensitive subpopulations of DRG neurone s can thus be distinguished on the basis of their peak [Ca2+](i) trans ient amplitudes, which appear to be associated with different rates of Ca2+ influx. (C) 1998 Elsevier Science Ireland Ltd. All rights reserv ed.