The effects of excessive heat on heat-activated membrane currents in cultured dorsal root ganglia neurons from neonatal rat

The effects of high temperature (53-61degreesC) on membrane currents (V-heat) or depolarization (V-heat) induced by noxious heat were studied in cultured dorsal root ganglia neurons from neonatal rats using the whole cell patch clamp technique, I-heat or V-heat produced by 3 s ramp, of he increasing temperature between 43 and 50degreesC exhibited a fast slope (Q(10) > 10) that was similar both during rising and falling temperature (n = 85). Temperatures exceeding 52degreesC resulted in slowdown in the recovery of I-heat, and the threshold for inducing I-heat was shifted to lower temperatures in successive trials, These high temperatures (54-60degreesC) caused a linear and incomplete recovery of I-heat (Q(10) decreased to <5; 4.5 +/- 0.4: n = 17) and in successive trials the threshold of I-heat decreased to temperatures close to that in the bath. The neurons, however, remained sensitive to capsaicin and to decreased extracellular pH. It is suggested that exposure of nociceptive neurons to excessive noxious heat results in an irreversible decrease of the energy barrier between the testing and activated state of the protein structures responsible for Generation of I-heat. This may explain the sensitization of nociceptors after heat injury. (C) 2002 International Association for the Study of Pain, Published by Elsevier Science B.V. All rights reserved.