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 α2δ1 subunits associate with calcium channels of IPANs and whether α2δ1 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 α subunits of N (α1B) and R (α1E) type calcium channels, and the auxiliary α2δ1 subunit, were expressed by IPANs. This is the first discovery of the α2δ1 subunit in enteric neurons; we therefore investigated its functional role, by determining effects of the α2δ1 subunit ligand, pregabalin, that inhibits currents carried by channels incorporating this subunit. Pregabalin (10 µmol L(-1)) reduced the action potential duration. The effect was not increased with increase in concentration to 100 µmol L(-1). If N channels were first blocked by ω-conotoxin GVIA (0.5 µmol 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 (α1B) channel-forming subunits that are associated with α2δ1 modulatory subunits and are inhibited by pregabalin, plus functional R (α1E) channels that are not sensitive to binding of pregabalin to α2δ subunits. The positive effects of pregabalin in irritable bowel syndrome (IBS) patients might be partly mediated by its effect on enteric neurons.