Study Of Purinergic P2 Receptors On Spontaneous Contraction And Its Mechanism In Gastric Antrial Smooth Muscle Of Guinea-pig

Gastrointestinal (GI) smooth muscles generally become relaxed when non-adrenergic non-cholinergic(NANC) nerves are stimulated. It has been considered that the relaxation is mediated by inhititory NANC neurotransmitters such as nitric oxide (NO), vasointestinal polypeptide (VIP), and adenosine 5'-triphosphate (ATP), which are released from enteric nerves of GI tract. Among them, ATP is now well established as an endogenous purinergic neurotransmitter on the GI tract and the urinary badder and as a cotransmitter of noradrenaline in sympathetic nerve theminals. Until now, ATP has been considered th most likely inhibitory NANC neurotransmitter in mammalian GI smooth muscles. Especially in th gastric fundus, ATP has been proposed as a major inhibitory neurotransmitter responsible for the receptive relaxation after meal. However, GI smooth muscles showed excitatory responses to ATP and its analogues in the guinea-pig ileum and in the rat colon muscalaris mucosae. In rat gastric fundus, exogenous ATP evoked abiphasic reponse, i.e., transient relaxation followed a by contraction. Consequently, these results imply that ATP acts not only as an inhibitory transmitter in GI smooth muscles.In order to investigate the role of non-adrenergic non-cholinergic nerves in regulating mechanical and electrical activity of gastric circular smooth muscle, the effects of ATP and its analogues on gastric motility and electrical activities were observed in guinea-pig. In organ bath system, isometric force of the circular smooth muscle of guinea-pig gastric antrum was measured. Electrical activity of the muscle was recorded using intracellular microelectrode. Electrical and mechanical activities were recorded by chart recorder. Membrane currents were recorded using whole-cell patch clamp techenique.Results 1. Endogenous purinogic agonist involved in regulation of gastric motilityElectric field stimulation is impotant method in study effect of nervous system on GI smooth muscles motility. In order to determine what neurotransmitters released...