Movements of sodium, potassium and water in rat diaphragm in vitro

Potassium induced potential changes in rat diaphragm muscle

The effect of different potassium concentrations on the membrane potential and membrane resistance of rat diaphragm muscle fibres was measured by means of a double sucrose gap method and a microelectrode technique. Concentration measurements showed that the muscle fibres gained sodium and lost potassium in the equilibration period. In the absence of external chloride changing the external potassium concentration from 2.8 mM to potassium-free caused a depolarization of the membrane of about 30 mV and a small increase in membrane resistance. This K-dependent potential change (K-response) was induced by ouabain, K-strophanthin, 2,4-dinitrophenol and cyanide, indicating that an energy requiring process is involved. The temperature dependence of the K-response found is consistent with this assumption. Variation in potassium permeability in the absence and presence of external potassium could account for only 13% of the K-response. The K-response amplitude appeared to depend on the external potassium and the internal sodium concentration. Hyperpolarization of the membrane could not only be produced after readmission of potassium but also after addition of thallium, the latter being more potent. Raising the external chloride concentration resulted in a decrease of the K-response and membrane resistance. The current, generating the K-response was shown to be hardly influenced by conditional polarization of the membrane. It is concluded from these results that the K-response is mainly due to the operation of an electrogenic sodium pump.

Further observations on metabolic alterations in the hypothermic rat

Further observations on metabolic alterations in fasted rats cooled under ice to rectal temperatures approximating 15 °C are reported. In the hypothermic rats, metabolism of injected lactic acid does not appear to be impaired. There is however: increased concentration of inorganic phosphorus in blood but not in liver; increased concentration of glutathione in liver but not in blood; increased plasma chloride concentration; decreased red cell potassium concentration; increased red cell water content; decreased plasma water content. Hypothermia, under these conditions, did not alter concentrations of liver acid-extractable glycogen, red cell sodium, plasma sodium, plasma potassium, nor serum calcium. Administration of urea in saline prior to cooling elevated plasma sodium and potassium concentrations in hypothermic rats. These observations are discussed in relation to previously reported effects of hypothermia on carbohydrate metabolite levels.