Na-Ca exchange current was measured at various concentrations of internal Na [( Na]i) and Ca [( Ca]i) using intracellular perfusion technique and whole-cell voltage clamp in single cardiac ventricular cells of guinea pig. Internal Ca has an activating effect on Nai-Cao exchange beginning at approximately 10 nM and saturating at approximately 50 nM with a half maximum [Ca]i (Km[Ca]i) of 22 nM (H...

Cardiac muscle fails to relax upon replacement of extracellular Ca 2 1 with Ba 2 1 . Among the manifold consequences of this intervention, one major possibility is that Na 1 -Ba 2 1 exchange is inadequate to support normal relaxation. This could occur due to reduced transport rates of Na 1 -Ba 2 1 exchange and/or by failure of Ba 2 1 to activate the exchanger molecule at the high affinity regul...

The inotropic and toxic effects of cardiac steroids are thought to result from Na(+)-K(+)-ATPase inhibition, with elevated intracellular Na(+)(Na)causing increased intracellular Ca(2+)(Ca) via Na-Ca exchange. We studied the effects of ouabain on cat ventricular myocytes in Na(+)-free conditions where the exchanger is inhibited. Cell shortening and Ca transients (with fluo 4-AM fluorescence) wer...

Verapamil (10(-6) M) significantly reduced a development of the membrane depolarization and the contracture which were induced by Na removal. The fully developed depolarization, after exposure to Na-free solution, was reduced greatly by verapamil, excess Ca (15 mM) or sodium nitroprusside (10(-6) M), but some depolarization still remained. This remaining depolarization was completely blocked by...

Calcium (Ca) dynamics are incorporated into a mathematical model of the principal cell in the cortical collecting tubule developed earlier in Strieter et al. (1992a. Am. J Physiol. 263:F1063-1075). The Ca components are modeled after the Othmer-Tang model for IP(3)-sensitive calcium channels (1993, in Experimental and Theoretical Advances in Biological Pattern Formation, 295-319). There are IP(...

A rise in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary artery smooth muscle cells (PASMC) is a trigger for pulmonary vasoconstriction and a stimulus for PASMC proliferation and migration. Multiple mechanisms are involved in regulating [Ca(2+)](cyt) in human PASMC. The resting [Ca(2+)](cyt) and Ca(2+) entry are both increased in PASMC from patients with idiopathic pulmonary arteri...

To investigate the hypothesis that Na(+) concentration in subplasmalemmal microdomains regulates Ca(2+) concentrations in cellular microdomains ([Ca](md)), the cytosol ([Ca](cyt)), and sarcoplasmic reticulum (SR; [Ca](sr)), we modeled transport events in those compartments. Inputs to the model were obtained from published measurements in descending vasa recta pericytes and other smooth muscle c...

Intracellular Ca(2+) is critical to the central clock of the suprachiasmatic nucleus (SCN). However, the role of Na(+)/Ca(2+) exchanger (NCX) in intracellular Ca(2+) concentration ([Ca(2+)]i) homeostasis in the SCN is unknown. Here we show that NCX is an important mechanism for somatic Ca(2+) clearance in SCN neurons. In control conditions Na(+)-free solution lowered [Ca(2+)]i by inhibiting TTX...

Palmer, Bradley M., Joshua M. Lynch, Steven M. Snyder, and Russell L. Moore. Renal hypertension prevents run training modification of cardiomyocyte diastolic Ca21 regulation in male rats. J Appl Physiol 90: 2063–2069, 2001.—The combined effects of endurance run training and renal hypertension on cytosolic Ca21 concentration ([Ca]c) dynamics and Na-dependent Ca21 regulation in rat left ventricul...

Cooper, P. J., M.-L. Ward, P. J. Hanley, G. R. Denyer, and D. S. Loiselle. Metabolic consequences of a species difference in Gibbs free energy of Na/Ca exchange: rat versus guinea pig. Am J Physiol Regulatory Integrative Comp Physiol 280: R1221–R1229, 2001.—The Gibbs free energy of the sarcolemmal Na/Ca exchanger (DGNa/Ca) determines its net Ca flux. We tested the hypothesis that a difference o...