Rat dorsal root ganglion neurones express different capsaicin-evoked Ca2+ transients and permeabilities to Mn2+

Capsaicin (1 microM) evoked [Ca2+]i transients in two-thirds of a Percoll-gradient enriched population of rat dorsal root ganglion (DRG) neurones. Amongst the capsaicin-sensitive neurones, 68% responded to capsaicin with peak [Ca2+]i transients of 681 +/- 67 nM, whereas the remaining neurones gave peak [Ca2+]i transients of 260 +/- 84 nM. In the presence of Mn2+ in Ca2+-free medium, capsaicin evoked quenching of fura-2 fluorescence, due to Mn2+ influx, in a similar proportion of neurones. Two patterns of capsaicin-sensitive Mn2+ quenching were observed: 72% of neurones showed rapid quenching (t1/2 of 18.3 +/- 4.1 s), whereas the remaining neurones had low quenching rates (t1/2 of 119 +/- 33 s). Distinct capsaicin-sensitive subpopulations of DRG neurones can thus be distinguished on the basis of their peak [Ca2+]i transient amplitudes, which appear to be associated with different rates of Ca2+ influx.