Diaphragm disuse reduces Ca2+uptake capacity of sarcoplasmic reticulum

Howell, Sandra, Wen-Zhi Zhan, and Gary C. Sieck.Diaphragm disuse reduces Ca2+uptake capacity of sarcoplasmic reticulum. J. Appl. Physiol. 82(1): 164–171, 1997.—Chronic phrenic tetrodotoxin (TTX) blockade and phrenic denervation (Dnv) of hamster diaphragm result in decreased maximum specific tension, prolonged contraction time, and improved fatigue resistance (W. Z. Zhan and G. C. Sieck. J. Appl. Physiol. 72: 1445–1453, 1992). An underlying increased relative contribution of type I fibers to total muscle mass appears to be consistent with, but does not completely account for, changes in contractile and fatigue properties. The present study was designed to evaluate a potential role for altered cellular Ca2+metabolism in the adaptive response of the diaphragm to chronic disuse. An analytic method based on simulation and modeling of long-term45Ca2+efflux data was used to estimate Ca2+ contents (nmol Ca2+/g wet wt tissue) and exchange fluxes (nmol Ca2+ ⋅ min−1 ⋅ g−1) for extracellular and intracellular compart...