Activation of protein kinase C by the capsaicin analogue resiniferatoxin in sensory neurones.

Resiniferatoxin and capsaicin are sensory neurone-specific excitotoxins that operate a common cation channel in nociceptors. Resiniferatoxin is structurally similar to capsaicin and to phorbol esters. Specific [3H]-resiniferatoxin binding, which was detected in the membrane (KD value 1.8 +/- 0.2 nM) but not cytosolic fraction of rat dorsal root ganglia, could not be displaced by phorbol 12,13-dibutyrate. Conversely, resiniferatoxin did not displace [3H]phorbol 12,13-dibutyrate binding in either the cytosolic or membrane fraction. Resiniferatoxin and capsaicin both caused translocation of protein kinase C in dorsal root ganglion neurones (EC50 value 18 +/- 3 nM). This translocation was greatly reduced but not abolished, in the absence of external Ca2+, suggesting that it was secondary to Ca2+ entry. Resiniferatoxin also caused direct activation of a Ca(2+)- and lipid-dependent kinase (or kinases) in the cytosolic fraction of dorsal root ganglia, at concentrations (100 nM to 10 microM) higher than required for displacement of [3H]resiniferatoxin binding or translocation of protein kinase C. Capsaicin (up to 10 microM) was unable to mimic this effect. These data imply that although resiniferatoxin-induced translocation of protein kinase C in dorsal root ganglion neurones was mainly indirect, it also caused direct activation of a protein kinase C-like kinase in these cells.