Intracellular sodium concentration and resting sodium fluxes of the frog heart ventricle

Abstract

SUMMARY1. Using 24Na to label the exchangeable sodium in the tissue and either [35S]sulphate or [14C]sucrose to label the extracellular spaces, the intracellular sodium concentration of frog heart ventricles was determined and found to be between about 5 and 10 m-mole/kg cell water.2. The intracellular potassium concentration, obtained by flamephotometric analysis, was approximately 163 m-mole/kg cell water.3. Two different methods were employed to study the sodium tracer efflux of resting heart ventricles. One involved a double-tracer technique, using 24Na to indicate the release of the exchangeable tissue sodium, and 35SO4 to indicate, approximately, the release of extra-myocardial sodium. In the other a comparison was made of the sodium release from the tissue when it contained sodium either at the normal concentration or at a concentration enhanced by exchange with intracellular potassium.4. The magnitude of the sodium efflux from heart fibres as measured by both methods was of the order 50-100 p-mole/cm2 sec. Simultaneously with this cellular efflux a substantial amount of sodium was released from extra-myocardial spaces and tissues.5. The net efflux of potassium ions from heart cells that occurred when heart ventricles were perfused with potassium-depleted fluids was determined. The results were used to obtain an indirect estimate, of about 2-3 p-mole/cm2 sec, for the resting sodium influx.6. The significance of these different values of sodium efflux and influx is discussed.

The effect of adrenaline on the tension developed in contractures and twitches of the ventricle of the frog

“…For some years it has been suggested that adrenaline increases sodium pumping (Biilbring, 1960) and there is some direct experimental evidence for this in frog's ventricle (Haas & Trautwein, 1963). This would be expected to decrease [Na]i and as a consequence cause a decrease in Pcag We could find no evidence in the literature that [Na]i does decrease and have so far been unable to demonstrate it directly, for the amount of sodium in the cells appears to be normally quite low (Keenan & Niedergerke, 1967) and not easy to detect.…”

“…Although there is little evidence for Ca storage tubules in frog's ventricle (which seems to have a simple structure, Keenan & Niedergerke, 1967), it is clear that mammalian heart muscle contains structures which accumulate Ca (see Lee, Ladinsky, Choi & Kasuya, 1966;Gertz, Hess, Lain & Briggs, 1967;Carsten, 1967) for these can readily be obtained as microsomes in vitro. Therefore these hearts contain a similar, although probably less active (Palmer & Posey, 1967), mechanism for Ca storage to that existing in skeletal muscle (see review by Sandow, 1965).…”

The interaction of sodium and calcium ions at the cell membrane and the control of contractile strength in frog atrial muscle.

“…We have preferred to ascribe a value of 7 mm to the [Na]i, i.e. the value determined by two flux studies on frog heart (Keenan & Niedergerke, 1967;Novotny & Bianchi, 1973) and close to the value obtained for mammalian myocardial cells with cationsensitive microelectrodes (Lee & Fozzard, 1975;Ellis, 1977) [Ca], is predicted by three different models of the Ca-Na exchange. In each case an [Na], is assumed to be 7 mm.…”

“…To account for the results of flux and contracture experiments, this notation was later developed into a carrier mediated exchange of two Na ions for one Ca ion across the sarcolemma (Niedergerke, 1963 a, b;Reuter & Seitz, 1968;Chapman, 1974;Miller & Moisescu, 1976;Chapman & Ellis, 1977). In the resting heart a low intracellular Ca concentration could be maintained by a simple exchange of one Ca+ for two Na2+ and would, at equilibrium, depend on [Ca] [Ca] = [Ca][Na]02 (1) When values for the Na and Ca concentrations in Ringer solution and an experi-0022-3751/80/1300-0669 $ 07.50 0 1980 The Physiological Society R. A. CHAPMAN AND J. TUNSTALL mentally determined value for intracellular Na concentration (Keenan & Niedergerke, 1967;Novotny & Bianchi, 1973) are inserted into eqn. (1), then an [Ca]i of over 10-6 M is predicted for the resting heart.…”

Sodium/calcium exchange in mammalian ventricular muscle: a study with sodium‐sensitive micro‐electrodes.

“…s. While this is a relatively large flux, Na fluxes in excess of this figure have been reported in cardiac tissue, e.g. for frog ventricle (Keenan & Niedergerke, 1967). In growth-orientated embryonic chick Wheeler, Horres & Lieberman (1982) find a Na efflux of 98 pmol/cm2 .…”