AN ANALYSIS OF THE POSITIVE INOTROPIC EFFECT OF ANAPHYLAXIS WITH POTASSIUM CONTRACTURE IN GUINEA PIG ATRIA, IN CONNECTION WITH THOSE OF INOTROPIC AGENTS

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The anaphylactic manifestation in the atrium isolated from a sensitized guinea pig is an increase in the contractile tension and in the beat rate (1, 2). Although the reaction is similar to the response of histamine, serotonin and adrenaline, it has not been blocked by antihistaminics (3) or DCI (4). So it is probable that the reaction occurs as a primary effect of anaphylactic manifestation taking place in cardiac muscle fibers (1).. It was also found in our laboratory that the time course of repolarization of the transmembrane action potential of proper atrial fiber of guinea pig is prolonged during anaphylaxis (5, 6). Furthermore, records of action potential of specialized fibers in the sinoatrial node during anaphylaxis showed the increased slope of the prepotential without any changes in its height (4). Similar observation of action potential change in intestinal segment during anaphylaxis has also been reported by Katsh and Marshall (7). So the prolongation of action potential duration in muscle fiber seems to be a ubiquitous change occurring in the anaphylactic manifestation.<BR> On the other hand, some results have been presented indicating that the duration of the action potential is one factor determining the contractility: changes in temperature alter both electrical and mechanical activity (8, 9), and tension and action potential duration decrease progressively as frequency increased in the rat atrium (9) and the guinea pig atrium (6), and several studies reported a change of comparable magnitude in action potential duration and contractility (10-13). These observations, however, do not imply that change in contractility must be associated with changes in action potential duration: that has also been confirmed in a number of studies (14-16). Therefore, the use of intracellular microelectrode technique to study electrical activity of cardiac muscle fibers has not provided much new information on the relationship between electrical and mechanical responses, and further investigation with different approaches is needed to discuss mechanism of the inotropic effect.<BR> In order to obtain further informations on the mechanism of anaphylactically induced inotropic action it seemed of interest to study the effect on contraction when muscle membrane is depolarized in the definite level. This can be done by studying the participation of anaphylactic manifestation on contractures of auricle preparation induced by application of depolarizing potassium chloride solution. However, attitudes of most drugs on the potassium contracture have not been reported with a few exception (17-19). The authors have also studied the effects of various agents having an inotropic action in guinea pig atria on the potassium contracture.
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AN ANALYSIS OF THE POSITIVE INOTROPIC EFFECT OF ANAPHYLAXIS WITH POTASSIUM CONTRACTURE IN GUINEA PIG ATRIA, IN CONNECTION WITH THOSE OF INOTROPIC AGENTS

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