The Force-Frequency Dependence in the Heart Papillary Muscle of Ground Squirrel as a Reflection of Changes in the Functional State of Animals during the Annual Cycle

Biophysics - Abstract—A study was conducted to explore the characteristics of the dependence of the contraction force (isometric mode at 30°C) on the frequency of stimulation...     

The effects of KB-R7943, an inhibitor of reverse Na<Superscript>+</Superscript>/Ca<Superscript>2+</Superscript> exchange,on the force of contraction of papillary muscles in the heart of the ground squirrel <Emphasis Type="Italic">Spermophilus undulatus</Emphasis>

We investigated the effect of KB-R7943, an inhibitor of the reverse mode of Na⁺/Ca²⁺ exchanger, on the force of isometric contractions, the contractile force–frequency relationship and post-rest potentiation (a qualitative parameter of Ca²⁺ levels in sarcoplasmic reticulum) in the right ventricle papillary muscles isolated from ground squirrel hearts during summer (June, n = 4) and autumn (October, n = 4) activities. In the presence of 1.8 mM Ca2+at 36°C, 1–1.5 hours-long treatment of the summer papillary muscles with KB-R7943 produced no significant effects on the contractile indices at the majority of stimulation frequencies. In the autumn papillary muscles KB-R7943 induced a 40–50% decrease in the force of contraction (negative inotropic effect) at low stimulation frequencies (0.1–0.3 Hz) without any significant effect at higher stimulation frequencies (0.4–3.0 Hz). Furthermore, in this group, KB-R7943 suppressed the post-rest potentiation of contractility by 50 ± 21% at pause durations exceeding 120 s. These observations indicate that KB-R7943 can affect Ca²⁺ levels in sarcoplasmic reticulum and that Na⁺/Ca2⁺ exchange may contribute to the physiological remodeling of intracellular Ca²⁺ homeostasis in myocardium of hibernating animals prior their transition to a hypometabolic torpid state.     

Activation of Sarcolemmal α2 Adrenoceptors Supports Са2+ Homeostasis and Prevents Ventricular Arrhythmia under Sympathetic Stress

Biophysics - Abstract—The body’s response to stress is mediated by the interaction of catecholamines with adrenergic α- and β-receptors. It has been established that, in...