Intracellular signalling pathway involved in ATP release from isolated smooth muscle cells.

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In recent investigations, ATP is known to exhibit a wide-variety of cell responses mediated by activation of P2X and P2Y-purinoceptors and, thus, seems to play roles of mediators to transfer signals to "cell to cell".In a series of our studies, it has been persented findings that stimulation of transmitters' receptors with noradrenaline and ACh elicits ATP release from smooth muscle segments.During the first year (1995) of the project, ATP released to superfusate from cultured smooth muscle cells from ileum and taenia coli of guinea-pig was measured by the luciferase method. The release of ATP was increased in the presence of alpha, beta-methylene ATP,bethanechol and peptides such as angiotensin II.The increased release was attenuated by respective antagonists. Accordingly, the findings suggest that ATP release comes from the smooth muscle cells.In 1996, the research project was focused on determination of inositol 1,4,5-trisphosphate (IP3) accumulation from the homogenate of ileal longitudinal muscles in the persence and absence of alpha, beta-methylene ATP.IP3 was measured by a radio-receptor assay using a IP3 assay kit (Amersham, TRK 1000). The P2-agonist enhanced the accumulation of IP3 in the homogenate. The enhanced accumulation was inhibited by blockade of phospholipase C and phosphoinositide turnover with neomycin and Li^+, respectively. The release of ATP evoked by alpha, beta-methylene ATP was insensitive to pertussis toxin and was counteracted by neomycin and spermine and by Li^+.Taken together, it is concluded that the enhancement of IP3 accumulation may be involved in the evoked release of ATP.