Distinctive actions of epidermal growth factor-urogastrone in isolated smooth muscle preparations from guinea pig stomach: differential inhibition by indomethacin.
ABSTRACT Epidermal growth factor-urogastrone (murine EGF-URO) caused concentration-dependent contractile responses in preparations of longitudinal and circular smooth muscle derived from guinea pig stomach. The actions of EGF-URO in these two preparations were distinguished in terms of the ability of indomethacin to block EGF-URO-mediated contraction completely in the longitudinal muscle preparation but not in the circular muscle preparation. The EC50 for EGF-URO was 2 to 5 nM in the longitudinal muscle preparations and 20 to 50 nM in the indomethacin-treated circular muscle preparation. The action of EGF-URO in the longitudinal preparation also was inhibited by ibuprofen, aspirin and by anti-inflammatory steroids possessing an 11-beta-hydroxyl; the corresponding steroids lacking the 11-beta-hydroxyl substituent were inactive. In contrast, little or no effect of the anti-inflammatory steroids on the EGF-URO-mediated response was observed in the indomethacin-treated circular muscle preparation. Partial inhibition (about 30%) of the EGF-URO-mediated contraction of the indomethacin-sensitive longitudinal preparation was caused by mepacrine and p-bromophenyl-acylbromide, whereas esculetine, tranylcypromine, prazosin, yohimbine and cyproheptadine had no effect. The action of EGF-URO in both preparations exhibited marked tachyphyllaxis, which could not be attributed either to the production of inhibitory factors or to the disappearance of EGF-URO from the organ bath. The response of both preparations required the presence of extracellular calcium and was inhibited largely (90%, longitudinal preparation) or in part (69%, indomethacin-treated circular preparation) by verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)
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ABSTRACT: Epidermal growth factor-urogastrone (EGF) caused a concentration-dependent contractile response in porcine ocular ciliary muscle preparations. The half-maximal contraction was observed at 23 ng/ml EGF (4 nM). The contractile action of EGF, which was not abolished by the removal of extracellular calcium, was not affected by atropine, tetrodotoxin, phentolamine and indomethacin. In addition to causing contractions on its own, the contractile action of EGF was potentiated in the presence of prostaglandin E1 and vasopressin. Our data point to a potential role for EGF in the regulation of ciliary muscle tension.European Journal of Pharmacology 01/1991; 191(3):245-51. DOI:10.1016/0014-2999(90)94156-R · 2.68 Impact Factor
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ABSTRACT: Vanadate, an inhibitor of tyrosine phosphatase activity, might induce gallbladder contraction through the stimulation of the tyrosine kinase pathway. The aim of this study was to characterize the effects of vanadate in the guinea pig gallbladder smooth muscle. Vanadate exerts contractile effects which are not mediated by neurotransmitter release. The tyrosine kinase inhibitor genistein nearly abolished vanadate contraction, suggesting that an increase in protein tyrosine phosphorylation mediates the actions of vanadate. This suggestion was confirmed by Western blot analysis. Vanadate contractions were reduced in the presence of methoxyverapamil or in Ca(2+)-free medium, suggesting that vanadate may induce Ca(2+) influx. Neither inactivation of the Na(+)/K(+) pump nor reversal of the Na(+)/Ca(2+) exchanger can account for vanadate's actions. Vanadate contractile effects were reduced by indomethacin, as well as mepacrine, the inhibitor of phospholipase A(2), but were not affected by phospholipase C inhibitors. Neither inhibitors of diacylglycerol lipase nor protein kinase C reduced the response induced by vanadate. These data indicate that the effects of vanadate on smooth muscle are mainly mediated by protein tyrosine phosphorylation and reveal a new link between tyrosine phosphorylation and arachidonic acid metabolism in the control of gallbladder smooth muscle contraction.Biochemical Pharmacology 06/2000; 59(9):1077-89. DOI:10.1016/S0006-2952(00)00237-9 · 4.65 Impact Factor
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ABSTRACT: We examined the effects of the tyrosine kinase (TK) inhibitors, genistein, and tyrphostin (RG-50864) on the contractile action of epidermal growth factor – urogastrone (EGF–URO), transforming growth factor-α (TGF-α), and other agonists in two smooth muscle bioassay systems (guinea pig gastric longitudinal muscle, LM, and circular muscle, CM). We also studied the inhibition by tyrphostin of EGF–URO stimulated protein phosphorylation in identical smooth muscle strips. The selective inhibition by genistein and tyrphostin of EGF–URO and TGF-α induced contraction, but not of carbachol- and bradykinin-mediated contraction, occurred at much lower concentrations (genistein, <7.4 μM (2 μg/mL); tyrphostin, <20 μM (4 μg/mL)) than those used in previously published studies with these TK inhibitors. In LM tissue, the IC50 values were for genistein 1.1 ± 0.1 μM (0.30 μg/mL; mean ± SEM) and 3.6 ± 0.5 μM (0.74 μg/mL) for tyrphostin, yielding a molar potency ratio (GS:TP) of 1:3 in the longitudinal preparation. In CM tissue, the IC50 values were 3.0 ± 0.3 μM (0.81 μg/mL) for genistein and 2.4 ± 0.2 μM (0.49 μg/mL) for tyrphostin, yielding a molar potency ratio (GS:TP) of 1.0:0.8 in the circular strips. The inhibition by genistein and tyrphostin of EGF–URO and TGF-α mediated contraction was rapid (beginning within minutes) and was reversible upon washing the preparations free from the enzyme inhibitors. In intact tissue strips studied under bioassay conditions, tyrphostin (40 μM) also blocked EGF–URO triggered phosphorylation of substrates detected on Western blots using monoclonal antiphosphotyrosine antibodies. In contrast with the results with EGF–URO, genistein at 7.4 μM (2 μg/mL) and tyrphostin at 20 μM (4 μg/mL) had no effect on either bradykinin (1 μM) or carbachol (1 μM) stimulated contraction in both LM and CM preparations. However, the contractile action of prostaglandin F2α (1 μM) was partially inhibited by genistein (7.4 μM), up to 10 ± 5% in the LM preparation and 35 ± 3% in the CM preparation (p < 0.05, LM vs. CM preparations) but not by tyrphostin (20 μM). Additionally, at the same concentrations, these tyrosine kinase inhibitors completely blocked angiotensin II mediated contraction in the LM preparation and partially inhibited contraction (43 ± 3%, mean ± SEM) in the CM preparation. The data suggest that tyrosine kinase activity plays an important role in EGF–URO induced contraction of gastric smooth muscle. Additionally, our results suggest that tyrosine kinase activity may also play a role in the signal transduction pathways by which smooth muscle contraction is induced by agonists such as angiotensin II and prostaglandin F2α which are known to act via a G-protein receptor coupled pathway.Key words: smooth muscle, tyrosine kinase, growth factor, angiotensin.Canadian Journal of Physiology and Pharmacology 02/2011; 70(1):85-93. DOI:10.1139/y92-012 · 1.55 Impact Factor