TYROSINE KINASE INHIBITORS SUPPRESS PROSTAGLANDIN F2-ALPHA-INDUCED PHOSPHOINOSITIDE HYDROLYSIS, CA2-MUSCLE( ELEVATION AND CONTRACTION IN IRIS SPHINCTER SMOOTH)

We investigated the effects of the protein tyrosine kinase inhibitors, genistein, tyrphostin 47, and herbimycin on prostaglandin F-2 alpha- and carbachol-induced inositol-1,4,5-trisphosphate (IP3) production, [ Ca2+](i) mobilization and contraction in cat iris sphincter smooth mus cle. Prostaglandin F-2 alpha and carbachol induced contraction in a co ncentration-dependent manner with EC50 values of 0.92 x 10(-9) and 1.7 5 x 10(-8) M, respectively. The protein tyrosine kinase inhibitors blo cked the stimulatory effects of prostaglandin F-2 alpha, but not those evoked by carbachol, on IP3 accumulation, [Ca2+](i) mobilization and contraction, suggesting involvement of protein tyrosine kinase activit y in the physiological actions of the prostaglandin. Daidzein and tyrp hostin A, inactive negative control compounds for genistein and tyrpho stin 47, respectively, were without effect. Latanoprost, a prostagland in F-2 alpha analog used as an antiglaucoma drug, induced contraction and this effect was blocked by genistein. Genistein (10 mu M) markedly reduced (by 67%) prostaglandin F-2 alpha-stimulated increase in [Ca2](i) but had little effect on that of carbachol in cat iris sphincter smooth muscle cells. Vanadate, a potent inhibitor of protein tyrosine phosphatase, induced a slow gradual muscle contraction in a concentrat ion-dependent manner with an EC50 of 82 mu M and increased IP3 generat ion in a concentration-dependent manner with an EC50 of 90 mu M. The e ffects of vanadate were abolished by genistein (10 mu M). Wortmannin, a myosin light chain kinase inhibitor, reduced prostaglandin F-2 alpha - and carbachol-induced contraction, suggesting that the involvement o f protein tyrosine kinase activity may Lie upstream of the increases i n [Ca2+](i) evoked by prostaglandin F-2 alpha. Further studies aimed a t elucidating the role of protein tyrosine kinase activity in the coup ling mechanism between prostaglandin F-2 alpha receptor activation and increases in intracellular Ca2+ mobilization and identifying the tyro sine-phosphorylated substrates will provide important information abou t the role of protein tyrosine kinase in the mechanism of smooth muscl e contraction, as well as about the mechanism of the intraocular press ure lowering effect of the prostaglandin in glaucoma patients. (C) 199 8 Elsevier Science B.V. All rights reserved.