BLOCKING EFFECTS OF PHENTOLAMINE ON L-TYPE CALCIUM CURRENT AND ATP-SENSITIVE POTASSIUM CURRENT IN GUINEA-PIG VENTRICULAR MYOCYTES

AIM: To study the effect of phentolamine on L-type calcium currents (I -Ca) and ATP-sensitive K+ currents (I-K,I-ATP) in ventricular myocytes . METHODS; I-Ca and I-K,I-ATP were observed using patch clamp techniqu es in whole-cell recording configuration, RESULTS: Phentolamine reduce d I-Ca of ventricular myocytes in concentration-dependent and voltage- independent manners. Phentolamine 5, 25, and 100 mu mol . L-1 decrease d I-Ca from 370 +/- 99 nA to 310 +/- 95 nA (17% block, n = 6, P <0.01) , from 230 +/- 98 nA to 180 +/- 73 nA (23% block, n = 5, P < 0.05), an d from 293 +/- 66 nA to 206 +/- 44 nA (30% block, n = 5, P <0.01), res pectively, without affecting the current-voltage relationship. Prazosi n 100 mu mol . L-1 and yohimbine 100 mu mol . L-1, which were specific blockers of nl and at adrenoceptors respectively, did not show the in hibitory effect on I-Ca, Phentolamine 100 mu mol . L-1 also inhibited the I-K,I-ATP induced by 2, 4-dinitrophenol (DNP) at 0 mV from 3.2 +/- 0.6 nA to 0.8 +/- 0.5 nA (75% block, n = 4, P < 0.01), CONCLUSION: Ph entolamine directly inhibits I-Ca and I-K,I-ATP in guinea pig ventricu lar myocytes.