Suramin affects capsaicin responses and capsaicin-noxious heat interactions in rat dorsal root ganglia neurones

The effect of suramin, an inhibitor of G protein regulated signalling, was studied on the membrane currents induced by noxious heat and by capsaicin in cultured dorsal root ganglia neurones isolated from neonatal rats. Whole-cell responses induced by a heat ramp (24-52 degrees C) were little affected by suramin. The noxious heat-activated currents were synergistically facilitated in the presence of 0.3 microM capsaicin 13.2-fold and 6.3-fold at 40 degrees C and 50 degrees C, respectively. In 65% of neurones, the capsaicin-induced facilitation was inhibited by 10 microM suramin to 35 +/- 6% and 53 +/- 6% of control at 40 degrees C and 50 degrees C (S.E.M., n = 15). Suramin 30 microM caused a significant increase in the membrane current produced by a nearly maximal dose (1 microM) of capsaicin over the whole recorded temperature range (2.4-fold at 25 degrees C and 1.2-fold at 48 degrees C). The results demonstrate that suramin differentially affects the interaction between capsaicin and noxious heat in DRG neurones and thus suggest that distinct transduction pathways may participate in vanilloid receptor activation mechanisms.