HEAT-INDUCED COBALT ENTRY - AN ASSAY FOR HEAT TRANSDUCTION IN CULTURED RAT DORSAL-ROOT GANGLION NEURONS

A histochemical stain to detect cobalt in cells was used to investigat e the ionic basis of heat transduction in mammalian primary afferent n eurons, Cultured dorsal root ganglion neurons from the adult rat were exposed to 10-min heat stimuli in an extracellular solution containing cobalt ions. When accumulated intracellular cobalt was precipitated, a subpopulation of neurons was darkly stained. The number of neurons s tained depended on the intensity of the heat stimulus, ranging from 1. 9% at 22 degrees C to 24.0% at 45 degrees C, a range of temperatures t ransduced by primary afferent nerve endings in vivo. Results of Trypan Blue exclusion experiments demonstrate that the heat-induced stain is not due to membrane damage, suggesting that heat opens a divalent-per meable ion channel, Agents that block many multivalent cation-permeabl e channels (lanthanum, ruthenium red and amiloride) did not reduce the number of cells that exhibited heat-induced cobalt staining, Heat-evo ked cobalt staining provides an in vitro model for the investigation o f the ionic mechanisms of thermal transduction in neurons. (C) 1997 IB RO.