Role of sodium-calcium exchange in regulation of intracellular calcium in nerve terminals

Journal Article · Mon Jun 01 04:00:00 EDT 1987 · Am. J. Physiol.; (United States)

OSTI ID:6862511

Sanchez-Armass, S; Blaustein, M P

Ca efflux from rat brain presynaptic nerve terminals (synaptosomes) was examined after loading the terminals with /sup 45/Ca during a brief depolarization, usually in media containing 20 ..mu..M Ca labeled with /sup 45/Ca, to assure a small (physiological) load. Efflux of /sup 45/Ca was very slow in the absence of external Na and Ca and was greatly accelerated by Na and/or Ca. The dependence of /sup 45/Ca efflux on external Na was sigmoid, with a Hill coefficient of approx. 4.5; this implies that more than two external Na ions are required to activate the efflux of one Ca ion. The external Na (Na/sub 0/)-dependent Ca efflux was inhibited by 1 mM external La, by low temperature, and by raising external K. With small Ca loads, the mitochondrial uncoupler, carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), had negligible effect on either Ca uptake or efflux; with large loads, however, FCCP reduced the depolarization-stimulated Ca uptake and increased the Na/sub 0/-dependent Ca efflux. These effects may be attributed to reduction of mitochondrial Ca sequestration. Mitochondria do not appear to sequester much Ca when the loads are smaller. Estimations of Ca efflux indicate that approx. 20% of a small /sup 45/Ca load may be extruded via Na/sup +/-Ca/sup 2 +/ exchange within 1 s; this corresponds to a net Ca efflux of approx. 110 pmol Ca x mg protein/sup -1/ x s/sup -1/. This rate of extrusion is equivalent to the net Ca gain when the terminals fire at a frequency of approx. 18/s. The data on the Ca efflux into Na- and Ca-free media indicate that the ATP-fueled Ca pump can only extrude approx. 10-20 pmol Ca x mg protein/sup -1/ x s/sup -1/. Thus the results imply that Na/sup +/-Ca/sup 2 +/ exchange plays an important role in helping to extrude the Ca that enters during activity.

• Research Organization: Univ. of Maryland School of Medicine, Baltimore (USA)
• OSTI ID: 6862511
• Journal Information: Am. J. Physiol.; (United States), Journal Name: Am. J. Physiol.; (United States) Vol. 252:6; ISSN AJPHA
• Country of Publication: United States
• Language: English

Related Subjects

551001* -- Physiological Systems-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALI METAL COMPOUNDS
ALKALINE EARTH ISOTOPES
ANIMAL CELLS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
BRAIN
CALCIUM 45
CALCIUM ISOTOPES
CATIONS
CELL CONSTITUENTS
CELL MEMBRANES
CENTRAL NERVOUS SYSTEM
CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPES
MAMMALS
MEMBRANE TRANSPORT
MEMBRANES
NERVE CELLS
NERVOUS SYSTEM
NUCLEI
ORGANS
PHYSIOLOGY
RADIOISOTOPES
RATS
RODENTS
SODIUM COMPOUNDS
SOMATIC CELLS
VERTEBRATES