Blocking effects of phentolamine on L-type calcium current and ATP-sensitive potassium current in guinea pig ventricular myocytes.
OBJECTIVE
To study the effect of phentolamine on L-type calcium currents (ICa) and ATP-sensitive K+ currents (IK,ATP) in ventricular myocytes.


METHODS
ICa and IK,ATP were observed using patch clamp techniques in whole-cell recording configuration.


RESULTS
Phentolamine reduced ICa of ventricular myocytes in concentration-dependent and voltage-independent manners. Phentolamine 5, 25, and 100 mumol.L-1 decreased ICa 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), and from 293 +/- 66 nA to 206 +/- 44 nA (30% block, n = 5, P < 0.01), respectively, without affecting the current-voltage relationship. Prazosin 100 mumol.L-1 and yohimbine 100 mumol.L-1, which were specific blockers of alpha 1 and alpha 2 adrenoceptors respectively, did not show the inhibitory effect on ICa. Phentolamine 100 mumol.L-1 also inhibited the IK,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).


CONCLUSIONS
Phentolamine directly inhibits ICa and IK,ATP in guinea pig ventricular myocytes.
Liang
Y
Y
Department of Physiology, Shanxi Medical University, Taiyuan, China.
Wu
B W
BW
Dun
W
W
D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006352:Heart Ventricles; D009206:Myocardium / Q000166:cytology*; D018408:Patch-Clamp Techniques; D010646:Phentolamine / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D011224:Prazosin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D015220:Calcium Channels; D015221:Potassium Channels; D015016:Yohimbine; D011224:Prazosin; D010646:Phentolamine