The sodium pump in skeletal muscle in relation to energy barriers

Abstract

In a previous paper (Carey, Conway & Kernan, 1959) it was shown that, when frog sartorii were immersed during the night in K-free RingerConway fluid containing 120 mM-Na, the average content of Na in the muscle was 59-0 + 0-7 m-equiv/kg (s.E. of mean for 166 expts). Three muscles were used for each experiment.On reimmersion for 2 hr at room temperature in similar fluid containing 104 mM-Na and 10 mM-K (referred to here as the 120,0/104,10 procedure) there was considerable active secretion of Na, which is in agreement with the results of Desmedt (1953). The secretion averaged 17-6 + 0-8 m-equiv Na/kg in a large number of experiments, allowing 2 m-equiv Na/kg for passive diffusion from the interspaces in the total Na loss. (In the oxygen-uptake experiments described here the conditions were somewhat different, and the average secretion was found to be 22 m-equiv Na/kg.)If the reimmersion fluid contained 120 mM-Na (the 120,0/120,10 procedure) there was, on the average, little or no excretion of sodium though a very occasional experiment might show it markedly. Also, if the K-free soaking fluid contained 104 mM-Na, and the reimmersion fluid contained also 104 mm-Na, there was likewise no significant Na secretion (Carey, et al. 1959).A partial explanation for this difference was given by the consideration that a secretion of Na in the second immersion, with 10 m r-K present, could be regarded as a restoration of the conditions following the effects of the K-free immersion. One would expect then that the limit of the secretion would be set by the Na levels in the muscles if 10 mM-K were present in both the soaking and the reimmersion fluids. A number of experiments carried out with 10 mM-K present throughout suggested that the maximum average loss of Na to be expected in the 120,0/104,10; 120,0/120,10 and the 104,0/104,10 procedures was 20-0 + 1-0; 3-6 + 3-5 and 7-8 + 1-1 m-equiv/kg respectively. The average experimental losses observed were 19-6 + 0-8, -5-2 + 9-6 and 1-0 + 0-9. The elucidation of the

Accumulation of caesium and rubidium in vivo by red and white muscles of the rat

“…The fact that ECS was more negative than the mean membrane potential measured here in plasma also indicated its active accumulation. As the critical energy barrier to sodium extrusion (Conway, Kernan & Zadunaisky, 1961) by sodium-rich muscles was found to be similar 202 B. P. KERNAN CAESIUM AND RUBIDIUM UPTAKE BY RAT MUSCLE 203 (Kernan, 1969) in the presence of K+ and Cs+ it seems that the latter cation may be as effective as the former in activating the sodium pump when these ions are present together in the external fluid and may therefore compete as effectively for carrier sites.…”

Spectroscopic studies of frog muscle during sodium uptake and excretion

“…The inhibitor p-chloromercuribenzoate was particularly effective in blocking Na transport (Table 2), and in this respect it resembled Na iodoacetate (Conway, Kernan & Zadunaisky, 1961), another powerful inhibitor of enzymes depending on -SH groups for their activity. 872 R. P. KERNAN SPECTROSCOPIC STUDIES OF ACTIVE TRANSPORT 873 Iodoacetate was found here to be so effective as an inhibitor of the dehydrogenases that it was used in preference to amytal to block electron transfer to the respiratory chain during oxidation of the muscle for examination of the oxidized spectrum (see Methods).…”

Some further observations on the electrogenic sodium pump in non‐myelinated nerve fibres

“…Acceleration of the sodium pump produced by a lowered electrochemical gradient as suggested for striated muscle (Conway, Kernan & Zadunaisky, 1961;Mullins & Frumento, 1963) cannot be important in C-fibres, for both the electrochemical gradient and the oxygen consumption were increased after addition of potassium (Rang & Ritchie, 1968a, b). However, when the electrochemical gradient was changed by polarizing current, the posttetanic hyperpolarization was affected (Rang & Ritchie, 1968b).…”