Phorbol Ester Modulation of Ca(2+) Channels Mediates Nociceptive Transmission in Dorsal Horn Neurones

Phorbol esters are analogues of diacylglycerol which activate C1 domain proteins, such as protein kinase C (PKC). Phorbol ester/PKC pathways have been proposed as potential therapeutic targets for chronic pain states, potentially by phosphorylating proteins involved in nociception, such as voltage-dependent Ca(2+) channels (VDCCs). In this brief report, we investigate the potential involvement of Ca(V)2 VDCC subtypes in functional effects of the phorbol ester, phorbol 12-myristate 13-acetate (PMA) on nociceptive transmission in the spinal cord. Effects of PMA and of selective pharmacological blockers of Ca(V)2 VDCC subtypes on nociceptive transmission at laminae II dorsal horn neurones were examined in mouse spinal cord slices. Experiments were extended to Ca(V)2.3(−/−) mice to complement pharmacological studies. PMA increased the mean frequency of spontaneous postsynaptic currents (sPSCs) in dorsal horn neurones, without an effect on event amplitude or half-width. sPSC frequency was reduced by selective VDCC blockers, ω-agatoxin-IVA (AgTX; Ca(V)2.1), ω-conotoxin-GVIA (CTX; Ca(V)2.2) or SNX-482 (Ca(V)2.3). PMA effects were attenuated in the presence of each VDCC blocker and, also, in Ca(V)2.3(−/−) mice. These initial data demonstrate that PMA increases nociceptive transmission at dorsal horn neurones via actions on different Ca(V)2 subtypes suggesting potential anti-nociceptive targets in this system.