Summary
The aim of this paper was to estimate the Ca content of the sarcoplasmic reticulum (s.r.) and to compare this with the amount of Ca which enters the cell via the calcium current in systole. The s.r. Ca content was measured electrophysiologically in voltage-clamped rat ventricular myocytes. Rapid application of caffeine produced a transient increase of [Ca2+]i which was accompanied by a transient inward Na-Ca exchange current. The integral of this current gives a measure of the Ca2+ pumped out of the cell by Na-Ca exchange. Ni2+ (5 mM) inhibited the current and decreased the rate of fall of [Ca2+]i to 32% of the control suggesting that Na-Ca exchange is responsible for 68% of Ca removal from the cytoplasm following the addition of caffeine. Correcting for the Na-Ca independent Ca removal suggests that the s.r. Ca content is equivalent to about 120 μmol per litre cell. Furthermore we estimate that, during systole, Ca entry into the cell via the sarcolemmal calcium current is equal to about 6 % of the Ca content of the s.r.
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References
Bassani RA, Bassani JWM, Bers DM (1992) Mitochondrial and sarcolemmal Ca2+ transport reduce [Ca2+]i during caffeine contractures in rabbit cardiac myocytes. J Physiol (Lond) 453:591–608.
Bers DM. Excitation-contraction coupling and cardiac contractile force. Dordrecht: Kluwer. 1991:
Callewaert G, Cleemann L, Morad M (1989) Caffeine-induced Ca2+ release activates Ca2+ extrusion via Na+-Ca2+ exchanger in cardiac myocytes. Am J Physiol 257:C147–152.
Fabiato A (1983) Calcium-induced release of calcium from the cardiac sarcoplasmic reticulum. Am J Physiol 245:1–14.
O'Neill SC, Donoso P, Eisner DA (1990) The role of [Ca2+]i and [Ca2+]i-sensitization in the caffeine contracture of rat myocytes: measurement of [Ca2+]i and [caffeine]i. J Physiol (Lond) 425:55–70.
O'Neill SC, Valdeolmillos M, Lamont C, Donoso P, Eisner DA (1991) The contribution of Na-Ca exchange to relaxation in mammalian cardiac muscle. Ann N Y Acad Sci 639:444–452.
Page E (1978) Quantitative ultrastructural analysis in cardiac membrane physiology. Am J Physiol 235:C147-C158.
Varro A, Hester SB, Eisner DA (1992) An estimate of the relative contributions of the sarcoplasmic reticulum and calcium current to contraction of isolated rat ventricular myocytes. J Physiol (Lond) 452:127P.
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Varro, A., Negretti, N., Hester, S.B. et al. An estimate of the calcium content of the sarcoplasmic reticulum in rat ventricular myocytes. Pflugers Arch. 423, 158–160 (1993). https://doi.org/10.1007/BF00374975
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DOI: https://doi.org/10.1007/BF00374975