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Effects of α1-Adrenergic Receptor Stimulation on Intracellular Na+ Activity and Twitch Force in Guinea-Pig Ventricular Muscles
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  • Effects of α1-Adrenergic Receptor Stimulation on Intracellular Na+ Activity and Twitch Force in Guinea-Pig Ventricular Muscles
저자명
Chae, Soo-Wan,Gong, Q.Y.,Wang, D.Y.,Lee, Chin-O.
간행물명
대한생리학회지
권/호정보
1995년|29권 2호(통권56호)|pp.203-216 (14 pages)
발행정보
대한생리학회|한국
파일정보
정기간행물|ENG|
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영문초록

The effects of α1-adrenergic receptor stimulation on membrane potential, intracellular Na+ activity, and twitch force were investigated in ventricular muscles from guinea-pig hearts. Action potentials, intracellular Na+ activity, and twitch force of ventricular papillary muscles were measured simultaneously under various experimental conditions. Stimulation of the α1-adrenergic receptor by phenylephrine produced variable changes in action potential duration, a slight hyperpolarization of the diastolic membrane potential, a decrease in intracellular Na+ activity, and a biphasic inotropic response in which a transient negative inotropic response was followed by a sustained positive inotropic response. These changes were blocked by prazosin, an antagonist of the α1-adrenergic receptor, but not by atenolol, an antagonist of the β-adrenergic receptor. This indicates that the changes in membrane potential, intracellular Na+ activity, and twitch force are mediated by stimulation of the α1-adrenergic receptor, but not by stimulation of β-adrenergic receptor. The decrease in intracellular Na+ activity was not observed in quiescent muscles, depending on the rate of the action pontentials in beating muscles. The intracellular Na+ activity decrease was substantially inhibited by tetrodotoxin. However, the decrease in intracellular Na+ activity was not affected by an inhibition of the Na+-K+ pump. Therefore, the decrease in intracellular Na+ activity mediated by the α1-adrenergic receptor appears to be due to a reduction of Na+ influx during the action potential, perhaps through tetrodotoxin sensitive Na+ channels. Our study also revealed that the decrease in intracellular Na+ activity might be related to the transient negative inotropic response. The intracellular Na+ activity decrease could lower intracellular Ca2+ through the Na+-Ca2+ exchanger and thereby produce a decline in twitch force.

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