Methods and findings in experimental and clinical pharmacology vol:13 issue:1 pages:29-36
The in vitro effects of the alpha-adrenergic receptor blockers naftopidil and urapidil in a concentration range of 1 nM-100 microM were investigated on various transmembrane cation transport systems in human erythrocytes, leukocytes and platelets. In order to elucidate possible calcium channel blocking action of naftopidil or urapidil, their in vitro effect on cytosolic free calcium concentration in human platelets was also investigated and compared to that of the calcium antagonist verapamil. Erythrocyte Na+,K(+)-cotransport and Na+,Li(+)-countertransport activity was inhibited by naftopidil. Urapidil and verapamil had no effect on these transport systems except that at the highest concentration (100 microM) verapamil had a small inhibitory effect (14%) on Na+,K(+)-cotransport activity. The erythrocyte anion carrier was decreased by naftopidil but not by verapamil and urapidil. No effect of naftopidil, urapidil and verapamil was observed on the Na+,K(+)-pump activity or on the number of active Na(+)-pump units in human erythrocytes, leukocytes or platelets. The increase in cytosolic free calcium concentration induced by thrombin was decreased by verapamil and naftopidil, but not by urapidil.