Interaction between excitatory and inhibitory metabotropic pathways in the guinea-pig antrum

Intracellular recordings were made from isolated bundles of the circular muscle layer of guinea-pig gastric antrum and the responses evoked by stimulating nitrergic nerve fibres were examined. Nitrergic inhibitory junction potentials (nitrergic-IJPs), evoked by trains of stimuli, had small amplitudes and were associated with a reduction in the rate of occurrence and amplitude of spontaneously occurring depolarizing potentials, termed unitary potentials. Nitrergic-IJPs were abolished either by membrane hyperpolarization or by 4, 4'-diisothiocyano-2, 2'-stilbene disulfonic acid (DIDS); both of these abolished the discharge of unitary potentials. Membrane depolarization increased the rate of discharge of unitary potentials so that they summed to give rise to are generative potential. Nitrergic nerve stimulation abolished regenerative potentials; this inhibition did not result from a change in threshold for the initiation of regenerative potentials,rather it occurred at some stage after the gating process. Inhibitory nitrergic nerve responses were blocked by L-nitroarginine (NOLA) and oxadiazolo quinoxalin-l-one (ODQ), an inhibitor of soluble guanylate cyclase. The observations suggest that the inhibition of regenerative potentials results from an interaction between an inhibitory and an excitatory metabotropic pathway.