Potentiation of adenosine A1 receptor-mediated inositol phospholipid hydrolysis by tyrosine kinase inhibitors in CHO cells

1 The effect of protein tyrosine kinase inhibitors on human adenosine A(1) receptor-mediated [H-3]-inositol phosphate ([H-3]-IP) accumulation has been studied in transfected Chinese hamster ovary cells (CHO-AI) cells. 2 In agreement with our previous studies the selective adenosine A(1) receptor agonist N-6-cyclopentyladenosine (CPA) stimulated the accumulation of [H-3]-IPs in CHO-Al cells. Pre-treatment with the broad spectrum tyrosine kinase inhibitor genistein (100 mu M; 30 min) potentiated the responses elicited by 1 mu M (199+/-17% of control CPA response) and 10 mu M CPA (234+/-15%). Similarly, tyrphostin A47 (100 mu M) potentiated the accumulation of [H-3]-IPs elicited by 1 mu M CPA (280+/-32%). 3 Genistein (EC50 = 13.7+/-1.2 mu M) and tyrphostin A47 (EC50 = 10.4+/-3.9 mu M) potentiated the [H-3]-IP response to 1 mu M CPA in a concentration-dependent manner. 4 Pre-incubation with the inactive analogues of genistein and tyrphostin A47, daidzein (100 mu M; 30 min) and tyrphostin Al (100 mu M; 30 min), respectively, had no significant effect on the accumulation of [H-3]-IPs elicited by 1 mu M CPA. 5 Genistein (100 mu M) had no significant effect on the accumulation of [H-3]-IPs produced by the endogenous thrombin receptor (1 u ml(-1); 100+/-10% of control response). In contrast, tyrphostin A47 produced a small augmentation of the thrombin [H-3]-IP response (148+/-13%). 6 Genistein (100 mu M) had no effect on the [H-3]-IP response produced by activation of the endogenous G(q)-protein coupled CCKA receptor with the sulphated C-terminal octapeptide of cholecystokinin (1 mu M CCK-8; 96+/-6% of control). In contrast, tyrphostin A47 (100 mu M) caused a small but significant increase in the response to 1 mu M CCK-8 (113 +/- 3% of control). 7 The phosphatidylinositol 3-kinase inhibitor LY 294002 (30 mu M) and the MAP kinase kinase inhibitor PD 98059 (50 mu M) had no significant effect on the [H-3]-IP responses produced by 1 mu M CPA and 1 mu M CCK-8. 8 These observations suggest that a tyrosine kinase-dependent pathway may be involved in the regulation of human adenosine Al receptor mediated [H-3]-IP responses in CHO-Al cells.