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Effects of contrast media and hyperosmolality on action potential of guinea pig papillary muscle
63 EFFECTS OF CONTRAST MEDIA AND HYPEROSMOLALITY ON ACTION POTENTIAL OF GUINEA PIG PAPILLARY MUSCLE. M. Sumikawa, Y. Hirata, K. Shimomura. Dept. Int. Med., National Cardiovascular Center, Suita, Osaka, Japan. The purpose of this study is elucidate the mechanism of electrocardiographic abnormalities caused by contrast media during angiocardiography. Effects of meglumine-Na diatrizoate (MD), contrast media, and hyperosmolar solutions(Tyrode's solution + sucrose)(S) on action potentials were investigsted in isolated guinea pig papillary muscle. MD first induced a remarkable shortening of action potential duration, a decrease in overshoot and a transient hyperpolarization, followed by a significant decrease in resting potential, Vmax and action potential amplitude. Most specimens showed marked prolongation of action potentials after reperfusion of Tyrode's solution. S induced a similar change of action potentials. These results suggests that effects of contrast media on ventricular myocardial cells are due to its hyperosmolarity.
64 EFFECTS OF C02+ AND DANTROLENE ON ELECTRICAL AND MECHANICAL OSCILLATIONS IN GUINEA-PIG VENTRICULAR MUSCLES. H. Kinoshita, S. Kawano, M. Hiraoka. Dept. Cardiovasc. Dis., MRI, Tokyo Medical and Dental University, Tokyo, Japan Oscillatory afterpotentials (OAPs) accompanied by aftercontractions (ACs) are believed to be produced by a cyclic release and uptake of Ca2+ from the store when the cells are made Ca2+-overload. We studied comparative effects of Co2+ and dantrolene-Na+ on these activitites. Membrane potential and isometric tension were simultaneously recorded when guinea-pig ventricular muscles were superfused with the 1 mM-K+, 3.6 mM-Ca2+ solution developping OAPs. 2 mM-Co2+ quickly suppressed OAPs, ACs and twitch to be less than 50% of the control, with some recovery of OAPs and ACs at longer exposure than 10 minutes. On the wash-out of Co 2+, OAPs and ACs recovered quickly but twitch did slowly. 2 x 10-S M dantroleneNa+ suppressed twitch by about 20% of the control, but did not affect OAPs and ACs. These results suggest that dantrolene may affect the depolarization-induced Ca2+release process.
64 EFFECTS OF C02+ AND DANTROLENE ON ELECTRICAL AND MECHANICAL OSCILLATIONS IN GUINEA-PIG VENTRICULAR MUSCLES. H. Kinoshita, S. Kawano, M. Hiraoka. Dept. Cardiovasc. Dis., MRI, Tokyo Medical and Dental University, Tokyo, Japan Oscillatory afterpotentials (OAPs) accompanied by aftercontractions (ACs) are believed to be produced by a cyclic release and uptake of Ca2+ from the store when the cells are made Ca2+-overload. We studied comparative effects of Co2+ and dantrolene-Na+ on these activitites. Membrane potential and isometric tension were simultaneously recorded when guinea-pig ventricular muscles were superfused with the 1 mM-K+, 3.6 mM-Ca2+ solution developping OAPs. 2 mM-Co2+ quickly suppressed OAPs, ACs and twitch to be less than 50% of the control, with some recovery of OAPs and ACs at longer exposure than 10 minutes. On the wash-out of Co 2+, OAPs and ACs recovered quickly but twitch did slowly. 2 x 10-S M dantroleneNa+ suppressed twitch by about 20% of the control, but did not affect OAPs and ACs. These results suggest that dantrolene may affect the depolarization-induced Ca2+release process.