Tyrosine kinase inhibitors suppress prostaglandin F 2α-induced phosphoinositide hydrolysis, Ca 2+ elevation and contraction in iris sphincter smooth muscle

Abstract

We investigated the effects of the protein tyrosine kinase inhibitors, genistein, tyrphostin 47, and herbimycin on prostaglandin F 2α- and carbachol-induced inositol-1,4,5-trisphosphate (IP 3) production, [Ca 2+] i mobilization and contraction in cat iris sphincter smooth muscle. Prostaglandin F 2α and carbachol induced contraction in a concentration-dependent manner with EC 50 values of 0.92×10 −9 and 1.75×10 −8 M, respectively. The protein tyrosine kinase inhibitors blocked the stimulatory effects of prostaglandin F 2α, but not those evoked by carbachol, on IP 3 accumulation, [Ca 2+] i mobilization and contraction, suggesting involvement of protein tyrosine kinase activity in the physiological actions of the prostaglandin. Daidzein and tyrphostin A, inactive negative control compounds for genistein and tyrphostin 47, respectively, were without effect. Latanoprost, a prostaglandin F 2α analog used as an antiglaucoma drug, induced contraction and this effect was blocked by genistein. Genistein (10 μM) markedly reduced (by 67%) prostaglandin F 2α-stimulated increase in [Ca 2+] 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 concentration-dependent manner with an EC 50 of 82 μM and increased IP 3 generation in a concentration-dependent manner with an EC 50 of 90 μM. The effects of vanadate were abolished by genistein (10 μM). Wortmannin, a myosin light chain kinase inhibitor, reduced prostaglandin F 2α- and carbachol-induced contraction, suggesting that the involvement of protein tyrosine kinase activity may lie upstream of the increases in [Ca 2+] i evoked by prostaglandin F 2α. Further studies aimed at elucidating the role of protein tyrosine kinase activity in the coupling mechanism between prostaglandin F 2α receptor activation and increases in intracellular Ca 2+ mobilization and identifying the tyrosine-phosphorylated substrates will provide important information about the role of protein tyrosine kinase in the mechanism of smooth muscle contraction, as well as about the mechanism of the intraocular pressure lowering effect of the prostaglandin in glaucoma patients.