Abstract
activity to hibernation. To date, any published data on the nature of rhythm-inotropic relationship in the myocardium of hibernating animals in this period are completely absent. Experiments were performed on the right ventricular papillary muscle isolated from ground squirrels ( C. undulatus ). The isolation, stimulation, and contraction amplitude ( A ) measurement were performed as described previously [11] at 30 ± 1°e . The steady-state force‐frequency relationships were studied in the frequency range from 0.1 to 1.0 Hz. The contraction amplitude of papillary muscles at a frequency of 0.1 Hz was taken as 100%. The maximum rest potentiation of contractility (in the range of 1 to 60 s), sometimes up to 600 s, was determined as an increment in the amplitude of the first post-rest contraction ( A 1 ) relative to the amplitude of the preceding steady-state contraction ( A 0 ) at a stimulation frequency of 0.8 Hz and calculated by the formula (( A 1 – A 0 )/ A 0 ) × 100, %) [14]. The mechanical restitution curves were obtained by plotting the increment in A 1 versus pause duration. The data are expressed as the mean and square error of the mean ( p < 0.05).
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