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...

Bullfrog sympathetic ganglion cells were capable of producing action potentials (Ca spikes) in an isotonic (84 mM) CaCl2 solution. The peak level of Ca spikes showed an approximately 30 mv increase with a 10-fold increase in the Ca concentration. Na as well as Ca ions were capable of acting as charge carriers during the production of action potentials in a solution containing relatively high Ca...

BACKGROUND The Na(+)/Ca(2+) exchange (NCX) extrudes Ca(2+) from cardiac myocytes, but it can also mediate Ca(2+) influx, load the sarcoplasmic reticulum with Ca(2+), and trigger Ca(2+) release from the sarcoplasmic reticulum. In ischemia/reperfusion or digitalis toxicity, increased levels of intracellular [Na(+)] ([Na(+)](i)) may raise levels of intracellular [Ca(2+)] ([Ca(2+)](i)) via NCX, lea...