EFFECTS OF TYROSINE KINASE INHIBITORS ON THE CONTRACTILITY OF RAT MESENTERIC RESISTANCE ARTERIES

1 A pharmacological characterization of tyrosine kinase inhibitors (TKI) belonging to two distinct groups (competitors at the ATP-binding site and the substrate-binding site, respectively) was performed, based on their effects on the contractility of rat mesenteric arteries. 2 Both the ATP-site competitors (genistein and its inactive analogue, daidzein) and the substrate-site competitors (tyrphostins A-23, A-47 and the inactive analogue, A-1) reversibly inhibited noradrenaline (NA, (10 mu M)) and KCl (125 mM) induced contractions, concentration-dependently. Genistein was slightly but significantly more potent than daidzein; the tyrphostins were all less potent than genistein, and there were no significant differences between the individual potencies. The tyrosine kinase substrate-site inhibitor bis-tyrphostin had no inhibitory effect. 3 Genistein, daidzein, A-23 and A-47 each suppressed the contraction induced by Ca2+ (1 mu M) in alpha-toxin permeabilized arteries. A-1 and bis-tyrphostin had little or no effect on contraction of the permeabilized arteries. 4 Genistein was significantly more potent than daidzein with respect to inhibition of the contraction induced by 200 nM Ca2+ in the presence of NA (100 mu M) and GTP (3 mu M). The effect of A-23, A-47, A-1 and bis-tyrphostin was similar in permeabilized arteries activated with Ca2+ (200 nM) + NA (100 mu M) + GTP (3 mu M) and permeabilized arteries activated with 1 mu M Ca2+. 5 Genistein (30 mu M) reduced the fura-2 measured intracellular calcium activity ([Ca2+](i)) in arteries stimulated with NA but had no effect on [Ca2+](i) in arteries stimulated with KCI (125 mM). 6 The potent effect of the TKIs in this study is consistent with a role for tyrosine kinases in the mechanisms which regulate both cytoplasmic Ca2+ levels and the effect of Ca2+ on the contractile apparatus in smooth muscle cells in resistance arteries. However, the results must be interpreted cautiously because the enzyme inhibitors may have a poor specificity in intact tissues and because the presumed inactive analogues had potent effects.