The effect of external sodium concentration on the sodium fluxes in frog skeletal muscle

Abstract

Ussing (1949) suggested that part of the observed Na efflux in frog muscle might result from a process that he termed 'exchange diffusion', involving a sodium for sodium exchange across the membrane. Thus, if a carrier with a high affinity for Na were confined to the membrane and able to diffuse across it only when it had formed a complex with Na, there would be a continual movement of labelled Na through the membrane without necessarily any simultaneous consumption of energy. If such a mechanism existed, complete removal of Na from the outside of the membrane might be expected to eliminate a substantial fraction of the total efflux of labelled Na, unless the cation substituted for Na+ could also form a complex with the carrier and thus move across the membrane. We therefore investigated the effect on the Na efflux of substituting choline or lithium for the sodium in the external medium, and found that in both cases the efflux was promptly reduced by about half when the sodium in the interfibre fluid was replaced by the foreign cation. This observation clearly warranted further analysis, and the changes in Na efflux were examined for test muscles with altered internal Na concentrations, and at various temperatures. The effect of partial replacement of external Na was also investigated and the resulting changes in Na efflux were compared with the parallel alterations in Na influx. The effect of removing external Na was found to add to that of removing external K, and the relative magnitude of the two effects was studied as a function of the Na content of the muscles.A preliminary report on this work was made at the XX International Physiological Congress (Swan & Keynes, 1956). METHODSMeasurements of sodium fluxes For measurement of effluxes, frog muscles were dissected free and exposed to Ringer's solution containing 4Na for about 3-5 hr. This period was calculated as sufficient for the specific activity of

The Effects of Sodium, Potassium and Calcium on Metabolism of Rat’s Cerebral Cortical Slice With or Without Electrical Stimulation

“…Then, the sodium influx, although a passive movement and not always in a linear manner, was said to vary with external sodium concentration (40,42). However, in the present experiment, the sodium efflux taking place in the unstimulated tissue in medium with little or no sodium should be considered to be a passive movement due to the disappearance of concentration gradient across the membrance.…”

“…However, in this experiment, as we have suspended the cerebral tissue slice in potassium-free medium during the pre incubation period, it may be said that the tissue slices have lost tissue potassium appre ciably during this period (33,35,41), and gained sodium (39,41,42). Using tracers also showed that the sodium efflux of the muscle and sepia axon decreased in potassium-free medium (39,40). Considering these experimental facts, the present results of the rise in inorganic phosphate and lactic acid levels in the unstimulated tissue with little or no potassium are supposed to have been induced by the increase in sodium adsorption in the tissue ; on the contrary, the respiratory and metabolic responses to electrical stimula tion were remarkably suppressed; this increase in sodium adsorption in the unstimulated tissue would have inversely reduced the responses to electrical stimulation.…”

Inward movement of sodium ions in resting and stimulated frog's sartorius muscle

“…It is clear from this figure that for a given change in [Na+]o the corresponding change in Na+ influx is more pronounced at low levels of [Na+]o than a concentration close to normal. This non-linearity of the Na+ influx has already been pointed out by Keynes & Swan (1959). In normal Ringer about 38 % of the total Na+ efflux is Na+-activated and strophanthidin-insensitive (Horowicz, Taylor & Waggoner, 1970;Venosa & Horowicz, 1973) showing the characteristics of the exchange diffusion mechanism proposed by Ussing (1949) and first demonstrated in muscle by Keynes & Swan (1959).…”

“…This non-linearity of the Na+ influx has already been pointed out by Keynes & Swan (1959). In normal Ringer about 38 % of the total Na+ efflux is Na+-activated and strophanthidin-insensitive (Horowicz, Taylor & Waggoner, 1970;Venosa & Horowicz, 1973) showing the characteristics of the exchange diffusion mechanism proposed by Ussing (1949) and first demonstrated in muscle by Keynes & Swan (1959). Since in normal Ringer the muscle fibres are close to steady state, the net Na+ flux being practically zero, one should expect that about 38 % of the Na+ ions moving inward do so via exchange diffusion.…”

“…In the remainder of this paper 'muscle weight' refers to the drained condition. Estimation of the surface membrane area per unit weight of muscle In order to compare the flux data of this work with those obtained in single fibres (Hodgkin & Horowicz, 1959 a), or in sartorii whose surface area per unit weight is known (Keynes & Swan, 1959), it was necessary to have an estimate of that relation in the muscles used here. Six muscles representative of the ones used in these experiments were weighed, and their lengths were measured.…”