AJP - Cell Physiology, Vol 235, Issue 1 25-C34, Copyright © 1978 by American Physiological Society
Energy coupling to sodium transport in frog skeletal muscle
R. J. Connett and E. T. Hays
In addition to a strophanthidin-sensitive (SS) sodium efflux, a large
component of the sodium efflux in freshly isolated frog skeletal muscle is
sodium-activated and strophanthidin-insensitive (SASI). The amount of
metabolic energy associated with sodium movement by each of these
components was measured and the coupling between sodium movement and
adenosine 5'-triphosphate (ATP) hydrolysis in muscle was calculated. Energy
production was blocked by iodoacetate and cyanide. Energy turnover was
estimated from the change in creatine phosphate (CrP) and ATP contents and
expressed as potential energy (PE = CrP + 2ATP). After metabolic poisoning
a linear fall of PE occurred (6.3 mumol/g.h). Metabolic poisoning had no
effect on the magnitude of the SS or SASI components of sodium efflux. In 2
h the sodium moved, and PE change due to the SS component was 4.35 and 1.66
mumol/g.h, respectively, which gave a coupling factor of 2.6. The amount of
sodium moved by the SASI component was similar to that moved by the SS
component in 2 h whereas no energy change was observed. It was, therefore,
concluded that sodium movement by the SASI component requires no energy
input.
