SODIUM, POTASSIUM, AND CHLORIDE CONCENTRATIONS AND FLUXES IN THE ISOLATED GIANT AXON OF HOMARUS

Abstract

Isolated giant axons from the esophogeal connective of the lobster, Homarus americanus were used in a systematic study of radioactive ion fluxes (resting and stimulated), normal resting ion concentrations, extracellular space, and resting membrane resistance. The cut ends of axons used for tracer outflux experiments were drawn into small end compartments. Suitable flow arrangements prevented radioactive ions from these cut ends from reaching the outflux collected for counting. The outflux chamber aiso kept the axon motionless under a meniscus of fluid at all times so that ouflux collection could proceed continuously without disturbing the axon. The results of these studies are as follows: The internal sodium and potassium concentrations in isolated lobster axons maintained in high calcium saline are 37.2 and 235 mM/Kg axon, and in artificial sea water are 76.1 and 277 mM/Kg axon. The internal chloride concentration for axons immersed in high calcium saline is about 45-55 mM/Kg axon. The resting Na, K, and Cl influxes are 6.8,10.8 and 9.5 pmoles/cin2-sec. The resting outfluxes are 3.2,15.0, and 9.3 pmoles/cm2-sec. Stimulation (5-20 imp/sec) increases Na influx and outflux by 6.5 and 1.3 pmoles/cm2-imp.: and K influx and outflux by 1.2 and 5.3 pmoles/cm2-imp. There is no effect of stimulation upon the chloride fluxes. The total membrane resistance calculated from tracer fluxes on the basis of the constant field equation is about 8500 ohm-cm2. The membrane resistance measured by electrical methods is 8257 ohm-cm2. The extracellular space amounts to a rim about 1-2 [mu] wide.