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The effect of substances releasing intracellular calcium ions on sodium‐dependent calcium efflux from guinea‐pig auricles.
Author(s) -
Jundt H,
Porzig H,
Reuter H,
Stucki J W
Publication year - 1975
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1975.sp010888
Subject(s) - efflux , caffeine , chemistry , calcium , sodium , biophysics , depolarization , ionophore , membrane potential , biochemistry , endocrinology , biology , organic chemistry
1. 45‐Ca efflux and resting tension were measured in isolated guinea‐pig auricles under conditions known to change the intracellular free Ca ion concentration. 2. In the presence of [Na]o, caffeine (2mM) increases 45‐Ca efflux, but does not produce a contracture, while in the absence of [Na]o and [Ca]o caffeine causes a contracture without increasing 45‐Ca efflux. Adrenaline (10‐minus5–10‐minus 4M) with or without theophylline (0–5‐1‐0mM) has no effect on either 45‐Ca efflux or resting tension. 3. In the presence of caffeine the rate of net efflux of Ca depends on [Na]o‐2. Caffeine contractures of muscles in Na‐free solution relax upon the addition of [Na]o. Relaxation is correlated with the increase in net efflux of Ca. 4. Cyanide (2mM) produces a variable increase in 45‐Ca efflux without a concomitant contracture in Na‐containing solutions, but in Na, Ca‐free solutions a large contracture occurs without significant increase in 45‐Ca efflux. 5. A large increase in 45‐Ca efflux and a contracture were observed with the ‘Ca‐ionophore’ X 537 A. 6. Changes in membrane potential (K‐depolarization) in hypertonic solutions have no significant effect on Na‐dependent 45‐Ca efflux, which is an agreement with an electroneutral 2:1 Na‐Ca exchange. 7. Cyanide and X 537 A both cause a considerable release of Ca ions from isolated guinea‐pig heart mitochondria, while caffeine has no effect. 8. The results suggest a powerful role of the Na‐Ca exchange system in reducing the intracellular Ca concentration after Ca release from intracellular stores.