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KMID : 0358619950290020203
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Korean Journal of Physiology
1995 Volume.29 No. 2 p.203 ~ p.216
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Effects of Receptor Stimulation on Intracellular Activity and Twitch Force in Guinea-Pig Ventricular Muscles
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Chae Soo-Wan
Gong Q.Y.
Wang D.Y.
Lee Chin-O
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Abstract
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The effects of receptor stimulation on membrane potential, intracellular activity, and twitch force were investigated in ventricular muscles from guinea-pig hearts. Action potentials, intracellular activity, and twitch force of ventricular papillary muscles were measured simultaneously under various experimental conditions. Stimulation of the receptor by phenylephrine produced variable changes in action potential duration, a slight hyperpolarization of the diastolic membrane potential, a decrease in intracellular 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 receptor, but not by atenolol, an antagonist of the receptor. This indicates that the changes in membrane potential, intracellular activity, and twitch force are mediated by stimulation of the receptor, but not by stimulation of receptor. The decrease in intracellular activity was not observed in quiescent muscles, depending on the rate of the action pontentials in beating muscles. The intracellular activity decrease was substantially inhibited by tetrodotoxin. However, the decrease in intracellular activity was not affected by an inhibition of the pump. Therefore, the decrease in intracellular activity mediated by the receptor appears to be due to a reduction of influx during the action potential, perhaps through tetrodotoxin sensitive channels. Our study also revealed that the decrease in intracellular activity might be related to the transient negative inotropic response. The intracellular activity decrease could lower intracellular through the exchanger and thereby produce a decline in twitch force.
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KEYWORD
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Guinea-pig ventricle, receptor, Intracellular activity, Membrane potential, Twitch force, Biphasic inotropic response, Phenylephrine, Prazosin
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