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The isometric contraction with its first derivatives and action potential of papillary muscles from right ventricles of rabbits were studied in media of bicarbonate buffered solutions that had the tonicities of 1.2, 1.4, 1.6 times that of the control. The results were as follows: 1. Intracellular negativity of resting membrane potential significantly increased in 1.4T, 1.6T from 78.5±6.2 mV to 83.3±4.7 and 89.8±6.0±mV respectively and the duration of action potential decreased, 233±32.1 in the control to 210.7±17.9 and 204.0±18.0 msec in 1.4T and 1.6T. 2. Isometric contraction showed a little change with a tendency to increase in 1.2T and then gradually decrease to 86.6±4.5% and 42.2±9.2% of the control in 1.4T, 1.6T. 3. +dT/dt decreased remarkably to 74.7±3.8%, 35.9±6.0% of the control in 1.4T, 1.6T and -dT/dt also decreased to 70.5±6.8%, 29.014.6% of the control. The above results suggested that the hypertonic solution on myocardium showed multiple effects simultaneously, an inhibition to the contractile element, alteration in intracellularly available calcium level and intracellular dehydration.
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