Blockade of L-type calcium channel in myocardium and calcium-induced contractions of vascular smooth muscle by CPU 86017

AIM: To assess the blockade by CPU 86017 on the L-type calcium channels in the myocardium and on the Ca^2+-related contractions of vascular smooth muscle. METHODS: The whole-cell patch-clamp was applied to investigate the blocking effect of CPU 86017 on the L-type calcium current in isolated guinea pig myocytes and contractions by KCl or phenylephrine (Phe) of the isolated rat tail arteries were measured. RESULTS: Suppression of the L-type current of the isolated myocytes by CPU 86017 was moderate, in time- and concentration-dependent manner and with no influence on the activation and inactivation curves. The IC50 was 11.5 μmol/L. Suppressive effect of CPU 86017 on vaso-contractions induced by KCl 100 mmol/L, phenylephrine 1 μmol/Lin KH solution (phase 1),Ca^2+ free KH solution ( phase 2), and by addition of CaCl2 into Ca^2+-free KH solution (phase 3) were observed. The IC50 to suppress vaso-contractions by calcium entry via the receptor operated channel (ROC) and Voltage-dependent channel (VDC) was 0.324μmol/L and 16.3μmol/L, respectively. The relative potency of CPU 86017 to suppress vascular tone by Ca^2+ entry through ROC and VDC is 1/187 of prazosin and 1/37 of verapamil, respectively.CONCLUSION: The blocking effects of CPU 86017 on the L-type calcium channel of myocardium and vessel are moderate and non-selective. CPU 86017 is approximately 50 times more potent in inhibiting ROC than VDC.