Effects of tyrosine kinase inhibitor, genistein, and phosphotyrosine—phosphatase inhibitor, orthovanadate, on Ca2+-free contraction of uterine smooth muscle of the rat

Abstract 1. 1. The effects of a protein-tyrosine kinase inhibitor, genistein, and a protein-tyrosine phosphatase inhibitor, orthovanadate, were tested on the Ca 2+ -free contraction of the estrogen-dominated rat, which has been proved to be induced mainly via protein kinase C entirely independently of Ca 2+ . 2. 2. Genistein (30 μM) significantly inhibited the contraction indicating participation of tyrosine kinase activity in the contraction. 3. 3. Orthovanadate caused contraction concentration-dependently and augmented the Ca 2+ -free contraction at concentrations of more than 1 μM. The contraction by orthovanadate was not inhibited so significantly by genistein (30 μM). 4. 4. Possible participation of tyrosine kinase activity in Ca 2+ -free contraction is discussed in addition to the formerly reported participation of protein kinase C.