The effects of an extracellular sodium (Na) concentration of 200 mM on function, ionic exchange, and water movements were examined in the vascularly perfused rabbit intraventricular septum. When the perfusate was switched from 142 mMNa to 200 mMNa, dP/ dt fell 20.4% over 2 minutes; dP/dt then recovered to the control level. The time course of the functional recovery correlated with the uptake o...

Zhang, Xue-Qian, Jianliang Song, Anwer Qureshi, Lawrence I. Rothblum, Lois L. Carl, Qiang Tian, and Joseph Y. Cheung. Rescue of contractile abnormalities by Na /Ca2 exchanger overexpression in postinfarction rat myocytes. J Appl Physiol 93: 1925–1931, 2002. First published August 16, 2002; 10.1152/japplphysiol.00583.2002.— Previous studies on myocytes isolated from rat hearts 3 wk after myocard...

Reverse-mode activity of the Na(+)/Ca(2+) exchanger (NCX) has been previously shown to play a prominent role in excitation-contraction coupling in the neonatal rabbit heart, where we have proposed that a restricted subsarcolemmal domain allows a Na(+) current to cause an elevation in the Na(+) concentration sufficiently large to bring Ca(2+) into the myocyte through reverse-mode NCX. In the pre...

potential propagated by axons. There are two other types of action potentials: (i) the Na!/Ca2!-dependent action potential present in axon terminals or heart muscle cells (Figure 4.2d), for example, where it is responsible for Ca2! entry and an increase of intracellular Ca2! concentration, a necessary prerequisite for neurotransmitter release (secretion) or muscle fibre contraction; and (ii) th...

Dynamical contraction of a slowly-rotating magnetized cloud is studied using the magnetohydrodynamical (MHD) simulations. In the isothermal stage (n ∼ < nA ∼ 10 cm), the cloud evolves similarly to that expected from Larson-Penston self-similar solution and experiences the run-away collapse. However, after the central density exceeds ∼ nA, an accretion disk is formed around the adiabatic core. J...

The excitation–contraction coupling cycle in cardiac muscle is initiated by an influx of Ca through voltage-dependent Ca channels. Ca influx induces a release of Ca from the sarcoplasmic reticulum and myocyte contraction. To maintain Ca homeostasis, Ca entry is balanced by efflux mediated by the sarcolemmal Na -Ca exchanger. In the absence of Na -Ca exchange, it would be expected that cardiac m...

To gain further insight into the excitation-contraction coupling mechanisms in hypertrophy, we studied rested-state contractions, rest decay curves, and rest potentiation under different experimental conditions using papillary muscles of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar and Wistar-Kyoto (WKY) rats. Under constant stimulation at 1.1 Hz, contractility and ...

The Na,K-ATPase α2 isoform is the predominant Na,K-ATPase in adult skeletal muscle and the sole Na,K-ATPase in the transverse tubules (T-tubules). In quiescent muscles, the α2 isozyme operates substantially below its maximal transport capacity. Unlike the α1 isoform, the α2 isoform is not required for maintaining resting ion gradients or the resting membrane potential, canonical roles of the Na...

Previous work demonstrated that Na(+)-K(+) pump activity within skeletal muscle is attenuated in myocardial infarction (MI). This may lead to enhanced interstitial K(+) concentration ([K(+)](o)) in the muscle. We tested the hypothesis that [K(+)](o) rises with muscle contraction and that, in rats with MI, the rate of rise in [K(+)](o) is greater than it is in control animals. Microdialysis prob...