Reversibility of high pressure effects on the contractility of skeletal muscle

High hydrostatic pressure induces slow contraction in mouse cardiomyocytes

Cardiomyocytes are contractile cells that regulate heart contraction. Ca2+ flux via Ca2+ channels activates actomyosin interactions, leading to cardiomyocyte contraction, which is modulated by physical factors (e.g., stretch, shear stress, and hydrostatic pressure). We evaluated the mechanism triggering slow contractions using a high-pressure microscope to characterize changes in cell morphology and intracellular Ca2+ concentration ([Ca2+]i) in mouse cardiomyocytes exposed to high hydrostatic pressures. We found that cardiomyocytes contracted slowly without an acute transient increase in [Ca2+]i, while a myosin ATPase inhibitor interrupted pressure-induced slow contractions. Furthermore, transmission electron microscopy showed that, although the sarcomere length was shortened upon the application of 20 MPa, this pressure did not collapse cellular structures such as the sarcolemma and sarcomeres. Our results suggest that pressure-induced slow contractions in cardiomyocytes are driven by the activation of actomyosin interactions without an acute transient increase in [Ca2+]i.

Effects of high-pressure acclimatization on silver eel (Anguilla anguilla, L.) slow muscle contraction

As the spawning migration of the eel is supposed to correspond to a long swimming activity at depth, patterns of slow red muscle contraction have been investigated in European silver eel (Anguilla anguilla L.) exposed for 3 weeks to 10.1 MPa hydrostatic pressure. The results show that pressure-acclimated eels (male and female) show a three-fold decrease in maximum isometric stress of twitch and tetanic contractions while time to peak force, time from peak force to 90% relaxation and ratio of twitch tension to tetanic tension remain unchanged. The observed modifications in slow red muscle mechanical properties do not impede the spawning migration of the eel and are possibly partially compensated by an improvement in the efficiency of oxidative phosphorylation. Effects of changes in membrane fluidity are also discussed.