Epinephrine stimulates Na-K pump by mediation of alpha-and beta-adrenoceptors in canine cardiac Purkinje fibers.
The effects of epinephrine on the twitch tension, intracellular Na+ activity (aiNa), and action potential were simultaneously investigated in an electrically driven canine Purkinje fiber. Epinephrine (0.3 microM) increased the twitch tension, duration of action potential (APD), and plateau height with a fall in aiNa. The twitch force increased during exposure and decreased during recovery. Propranolol (3 microM) or lidocaine (10 microM) decreased the twitch tension, APD, and aiNa when added to the bathing solution alone. They partially inhibited the effects of epinephrine (0.3 microM) on the development of the twitch tension and action potential and on the decrease of aiNa. Phentolamine (2 microM) reduced the twitch tension and plateau height of the action potential but failed to eliminate the action of epinephrine on the fibers. The combined action of phentolamine and epinephrine abbreviated the APD. The effect of epinephrine on the decrease of aiNa was entirely suppressed when the fiber was pretreated with propranolol (1 microM) and phentolamine (1 microM) or in a potassium-depleted solution. The results indicate that epinephrine exerts effects on the canine Purkinje fiber by the mediation of alpha-and beta-adrenoceptors. Adrenoceptor stimulation of both types is involved in the positive inotropic effect and the activation of the sarcolemmal Na-K pump.
Yang
J M
JM
Department of Physiology and Biophysics, National Defense Medical Center, Taipei, Taiwan, R.O.C.
Chung
K T
KT
D000818:Animals; D004285:Dogs; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D066298:In Vitro Techniques; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects* / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D008012:Lidocaine; D011433:Propranolol; D000254:Sodium-Potassium-Exchanging ATPase; D004837:Epinephrine; D010646:Phentolamine