Force-frequency relationship and rest potentiation in papillary muscles of Siberian ground squirrel in the period of preparation to hibernation

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).