Na transport across a preparation of sheep omasum was studied. All tissues exhibited a serosa-positive short-circuit current ( I sc), with a range of 1-4 μeq ⋅ h-1 ⋅ cm-2. A Michaelis-Menten-type kinetic was found between the Na concentration and the I sc(Michaelis-Menten constant for transport of Na = 6.7 mM; maximal transport capacity of Na = 4.16 μeq ⋅ h-1 ⋅ cm-2). Mucosal amiloride (1 mM), ...

Xie Y, Ottolia M, John SA, Chen J, Philipson KD. Conformational changes of a Ca -binding domain of the Na /Ca exchanger monitored by FRET in transgenic zebrafish heart. Am J Physiol Cell Physiol 295: C388–C393, 2008. First published June 11, 2008; doi:10.1152/ajpcell.00178.2008.—The Na /Ca exchanger is the major Ca extrusion mechanism in cardiac myocytes. The activity of the cardiac Na /Ca exch...

We have studied the interaction of physiological ligands other than Nai and Ca; with the Ca pump and Na/Ca exchange in internally dialyzed squid axons. The results show the following. (a) Internal Mg` is an inhibitor of the Na,,-dependent Ca efflux . At physiological me, (4 mM), the inhibition amounts to ~50%. The inhibition is partial and noncompetitive with Ca;, and is not affected by Nai or ...

Kim, Moon Young, Geun Hee Seol, Guo Hua Liang, Ji Aee Kim, and Suk Hyo Suh. Na -K pump activation inhibits endothelium-dependent relaxation by activating the forward mode of Na /Ca exchanger in mouse aorta. Am J Physiol Heart Circ Physiol 289: H2020–H2029, 2005. First published July 1, 2005; doi:10.1152/ajpheart.00908.2004.—The effect of Na -K pump activation on endothelium-dependent relaxation...

Background—The Na/Ca exchange (NCX) extrudes Ca from cardiac myocytes, but it can also mediate Ca influx, load the sarcoplasmic reticulum with Ca, and trigger Ca release from the sarcoplasmic reticulum. In ischemia/ reperfusion or digitalis toxicity, increased levels of intracellular [Na] ([Na]i) may raise levels of intracellular [Ca ] ([Ca]i) via NCX, leading to cell injury and arrhythmia. Met...

The activity of the cardiac Na(+)/Ca(2+) exchanger (NCX1.1) undergoes continuous modulation during the contraction-relaxation cycle because of the accompanying changes in the electrochemical gradients for Na(+) and Ca(2+). In addition, NCX1.1 activity is also modulated via secondary, ionic regulatory mechanisms mediated by Na(+) and Ca(2+). In an effort to evaluate how ionic regulation influenc...

Olfactory receptor neurons (ORNs) from the squid, Lolliguncula brevis, respond to the odors l-glutamate or dopamine with increases in internal Ca(2+) concentrations ([Ca(2+)](i)). To directly asses the effects of increasing [Ca(2+)](i) in perforated-patched squid ORNs, we applied 10 mM caffeine to release Ca(2+) from internal stores. We observed an inward current response to caffeine. Monovalen...

The hypothesis that Na(+) influx during the action potential (AP) activates reverse Na(+)-Ca(2+) exchange (NCX) and subsequent entry of trigger Ca(2+) is controversial. We tested this hypothesis by monitoring intracellular Ca(2+) before and after selective inactivation of I(Na) prior to a simulated action potential in patch-clamped ventricular myocytes isolated from adult wild-type (WT) and NCX...

Axons freshly dissected from living specimens of the tropical squid Dorytheutis plei have a calcium content of 68 tzmol/kg of axoplasm. Fibers stimulated at 100 impuises/s in 100 mM Ca seawater increase their Ca content by 150/zmol/ kg.min; axons placed in 3 Ca (choline) seawater increase their Ca content by 12 /zmol/kg.min. Axons loaded with 0.2-1.5 mmol Ca/kg of axoplasm extruded Ca with a ha...

The presence of a detectable Ca current during the excitation of a cardiac fiber implies that the Ca lost during the resting interval of the duty cycle must also be detectable. Ca outward movement appears to be effected by Na/Ca exchange when more Na enters than Ca leaves per cycle, thus making the mechanism electrogenic. Since Na/Ca exchange can move Ca either inward or outward depending on th...