Abstract
Pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are structurally related peptides showing 68% homology in the sequence of their amino-acid residual. Both peptides are supposed to be involved in regulation of gastrointestinal motility. In fact, it is reported that PACAP causes membrane depolarizations in almost of AH neurons and in a small proportion of S neurons in the myenteric plexus of guinea-pig small intestine. Since VIP is known to exert multiple actions on enteric neurons, the present electrophysiological study was undertaken to examine this possibility for PACAP. Myenteric plexus-longitudinal muscle preparations were removed from the ileum of adult guinea-pigs. Intracellular recordings were made from myenteric neurons by using glass-capillary microelectrodes. Although there are two bioactive forms, PACAP 27 and 38, PACAP 27 was applied with superfusion at concentrations between 10 nM and 1μM. PACAP 27 caused membrane depolarizations in 8 of 11 AH neurons and in 2 of 2 S neurons, associated with action potentials from neuron to neuron. Furthermore, the peptide induced membrane hyperpolarizations in two AH neurons, and inhibited amplitudes of fast EPSPs observed from one S neuron. It was concluded that PACAP modulated neuronal activity possibly via multiple pathways in the myenteric plexus which regulates gut motility. [Jpn J Physiol 55 Suppl:S191 (2005)]
