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Spontaneously hypertensive rats (SHR) are used to evaluate the myofilament calcium sensitivity-associated alteration in troponin-1 (Tn-1) phosphorylation and the expression of troponin isoforms during the evolution to decompensated cardiac hypertrophy. Results indicate that Tn-1 phosphorylation upon beta adrenergic stimulation of myocytes decreased among SHRs. The implications of these findings are discussed.

A study was performed to compare the baseline and protein kinase A (PKA)-dependent troponin I (TnI) phosphorylation in left ventricular myocytes from hearts of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Phosphorylation of TnI by PKA was believed to reduce myofilament Ca2+ sensitivity. Results indicated that after activation of the beta-adrenergic mechanism, PKA-dependent TnI phosphorylation from the SHR group was greater than in WKY coupled with decreased Ca2+ sensitivity of actomyosin ATPase activity.

A study was initiated to determine effects of mitochondrial metabolism on mitochondrial calcium (Ca) uptake during physiological processes. Mensuration of changes in the left ventricular function, pyruvate dehydrogenase (PDH) activity and mitochondrial Ca content was done in perfused hamster hearts frozen during systole. Results indicated that no relevant change was seen in mitchondrial Ca content during isoproterenol activation and increased perfusion pressure.

Diseases of striated muscle linked to intermediate filament (IF) proteins are associated with defects in the organization of the contractile apparatus and its links to costameres, which connect the sarcomeres to the cell membrane. Here we study the role in skeletal muscle of synemin, a type IV IF protein, by examining mice null for synemin (synm-null). Synm-null mice have a mild skeletal muscle phenotype. Tibialis anterior (TA) muscles show a significant decrease in mean fiber diameter, a decrease in twitch and tetanic force, and an increase in susceptibility to injury caused by lengthening contractions. Organization of proteins associated with the contractile apparatus and costameres is not significantly altered in the synm-null. Elastimetry of the sarcolemma and associated contractile apparatus in extensor digitorum longus myofibers reveals a reduction in tension consistent with an increase in sarcolemmal deformability. Although fatigue after repeated isometric contractions is more marked in TA muscles of synm-null mice, the ability of the mice to run uphill on a treadmill is similar to controls. Our results suggest that synemin contributes to linkage between costameres and the contractile apparatus and that the absence of synemin results in decreased fiber size and increased sarcolemmal deformability and susceptibility to injury. Thus synemin plays a moderate but distinct role in fast twitch skeletal muscle., (Copyright © 2015 the American Physiological Society.)