Postreceptor regulation of the trophic action of gastrin is not fully elucidated. Tyrosine kinase (Tyr-kinase) has been associated with receptors of a number of growth factors and plays an important role in regulation of cellular growth within the gastrointestinal tract. The aim of this study was to determine, whether Tyr-kinase plays a role in mediating the growth promoting action of gastrin and whether phospholipase C (PLC) is involved in the signal transduction pathway. Colonocytes isolated from Fischer 344 rats were incubated for 2 min with gastrin (10-8 M) and assayed for Tyr-kinase and PLC activities. Incubations with gastrin resulted in 60%-70% rise in Tyr-kinase and 150%-200% rise in PLC activities over the corresponding basal levels. When processed separately, in proximal colon Tyr-kinase activation by gastrin was 15%-20%, while in distal colon 70%-80% as compared to the buffer control. Gastrin activation of both Tyr-kinase and PLC was abolished by Tyr-kinase inhibitor, tyrphostin-25 (3.2 nM) and was not affected by staurosporine (20 ng/ml). We conclude that Tyr-kinase is involved in the mechanism of trophic action of gastrin, and PLC activation appears to be the next step in the signal transduction pathway.
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