Identification of subunits of voltage-gated calcium channels and actions of pregabalin on intrinsic primary afferent neurons in the guinea-pig ileum

Background The intrinsic primary afferent neurons (IPANs) in the intestine are the first neurons of intrinsic reflexes. Action potential currents of IPANs flow partly through calcium channels, which could feasibly be targeted by pregabalin. The aim was to determine whether pregabalin-sensitive alpha 2 delta 1 subunits associate with calcium channels of IPANs and whether alpha 2 delta 1 subunit ligands influence IPAN neuronal properties. Methods We used intracellular electrophysiological recording and in situ hybridisation to investigate calcium channel subunit expression in guinea-pig enteric neurons. Key Results The alpha subunits of N (alpha 1B) and R (alpha 1E) type calcium channels, and the auxiliary alpha 2 delta 1 subunit, were expressed by IPANs. This is the first discovery of the alpha 2 delta 1 subunit in enteric neurons; we therefore investigated its functional role, by determining effects of the alpha 2 delta 1 subunit ligand, pregabalin, that inhibits currents carried by channels incorporating this subunit. Pregabalin (10 mu mol L-1) reduced the action potential duration. The effect was not increased with increase in concentration to 100 mu mol L-1. If N channels were first blocked by omega-conotoxin GVIA (0.5 mu mol L-1), pregabalin had no effect on the residual inward calcium current. Reduction of the calcium current by pregabalin substantially inhibited the after-hyperpolarising potential (AHP) and increased neuron excitability. Conclusion & Inferences Intrinsic primary afferent neurons express functional N (alpha 1B) channel-forming subunits that are associated with alpha 2 delta 1 modulatory subunits and are inhibited by pregabalin, plus functional R (alpha 1E) channels that are not sensitive to binding of pregabalin to alpha 2 delta subunits. The positive effects of pregabalin in irritable bowel syndrome (IBS) patients might be partly mediated by its effect on enteric neurons.