Modulation of Na/sup +/-Ca/sup 2 +/ exchange in sarcolemmal vesicles by intravesicular Ca/sup 2 +/

Journal Article · Wed Dec 31 23:00:00 EST 1986 · Am. J. Physiol.; (United States)

OSTI ID:6409431

Reeves, J P; Poronnik, P

When cardiac sarcolemmal vesicles were incubated at 37/sup 0/C in 160 mM NaCl containing 0.5 mM CaCl/sub 2/ and subsequently assayed for Na-Ca exchange activity, they exhibited a threefold increase in the initial rate of /sup 45/Ca/sup 2 +/ uptake compared with vesicles incubated without added CaCl/sub 2/. Removal of endogenous Ca/sup 2 +/ by incubation of the vesicles with 0.1 mM ethylene-bis(..beta..-aminoethylether)-N,N'-tetraacetic acid (EGTA) resulted in a 35% inhibition in exchange activity. The pretreatment with CaCl/sub 2/ produced an acceleration of Na-Ca exchange activity rather than an increase in Ca/sup 2 +/ uptake due to Ca-Ca exchange. Pretreatment of the vesicles with CaCl/sub 2/ lowered the apparent K/sub m/ of the exchange system for Ca/sup 2 +/. The effects of the Ca treatment were reversed by subsequently incubating the vesicles with EGTA. In contrast to the effects of intravesicular Ca/sup 2 +/ on Na/sub i/-dependent Ca/sup 2 +/ uptake, external Ca/sup 2 +/ had no effect on Na/sub 0/-dependent Ca/sup 2 +/ efflux. The results suggest that an understanding of the kinetics of the Na-Ca exchange system may be hampered by the autoacceleration of exchange activity that occurs during initial rate measurements as Ca/sup 2 +/ accumulates within the vesicles. This phenomenon may contribute to the variability that exists among different vesicle preparations in their apparent K/sub m/ values for Ca/sup 2 +/.

• Research Organization: Roche Institute of Molecular Biology, Nutley, NJ
• OSTI ID: 6409431
• Journal Information: Am. J. Physiol.; (United States), Journal Name: Am. J. Physiol.; (United States) Vol. 252:1; ISSN AJPHA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
ALKALI METAL COMPOUNDS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BODY
CALCIUM 45
CALCIUM CHLORIDES
CALCIUM COMPOUNDS
CALCIUM HALIDES
CALCIUM ISOTOPES
CARDIOVASCULAR SYSTEM
CATIONS
CATTLE
CHARGED PARTICLES
CHLORIDES
CHLORINE COMPOUNDS
DAYS LIVING RADIOISOTOPES
DOMESTIC ANIMALS
DOSE-RESPONSE RELATIONSHIPS
EVEN-ODD NUCLEI
HALIDES
HALOGEN COMPOUNDS
HEART
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPES
KINETICS
MAMMALS
MEMBRANE TRANSPORT
NUCLEI
ORGANS
PHYSIOLOGY
RADIOISOTOPES
REACTION KINETICS
RUMINANTS
SODIUM CHLORIDES
SODIUM COMPOUNDS
VERTEBRATES