ISSN:
1432-1424
Keywords:
sodium/calcium exchange
;
excitation-contraction coupling
;
sarcolemma
;
membrane potential
;
sodium
;
calcium
;
heart
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The effect of membrane potential on sodium-dependent calcium uptake by vesicles in an isolated cardiac sarcolemma preparation was examined. Initial time course studies showed that the reaction deviated from initial velocity conditions within minutes. This appeared to be due, in part, to loss of the sodium gradient. Assays carried out to 10 sec revealed a linear component of uptake (2 to 10 sec) and a faster component (complete by 2 sec). The latter was eliminated by loading the preparation with ethyleneglycol-bis-(β-aminoethyl ether)N,N′-tetraacetic acid (EGTA). This maneuver did not affect the slow component, and subsequent studies used preparations containing EGTA. Potassium Nernst potentials (E K), established by potassium gradients in the presence of valinomycin, were varied from −100 to +30 mV by changing [K+] o from 1.18 to 153.7mM ([K+] i =50mM). The initial velocity of sodium-dependent calcium uptake was stimulated twofold by changingE K from −100 to 0 mV and another twofold by raisingE K from 0 to +30 mV. For the total range ofE K and [K+] o , 32 to 36% of the increase appeared to reflect stimulation by extravesicular potassium. The remainder appeared to be due to membrane potential. The profile of sodium-dependent calcium uptake versusE K suggested that calcium influx through electrogenic sodium/calcium exchange may be much more affected by the positive region of the cardiac action potential than by the negative region.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01871384
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