Abstract
Giant axons from the squid were injected with 1.5 M cesium sulfate solutions containing the radioactive isotopes 42K and 134Cs. These axons, when stimulated, gave characteristic long duration action potentials lasting between 5 and 45 msec. The effluxes of 42K and 134Cs were measured both under resting conditions and during periods of repetitive stimulation. During the lengthened responses there were considerable increases in potassium efflux but only small increases in cesium efflux. The selectivity of the delayed rectification process was about 9 times greater for potassium ions than for cesium ions. The data suggest that internal cesium ions inhibit the outward potassium movement occurring during an action potential. The extra potassium effluxes taking place during excitation appear to be reduced in the presence of cesium ions to values between 7 and 22% of those expected in the absence of cesium inhibition.
Highlights
Giant axons from the squid were injected with 1.5 Mcesium sulfate solutions containing the radioactive isotopes 42K and '34Cs
If the series of alkali cations K+, Rb+, Cs+ is considered, it seems evident that, in the squid axon, K+ and Rb+ tend to behave in a similar manner while the Cs+ ion gives rise to marked differences in behavior
Pickard et al (1964) observed little if any depolarizing action when squid axons were bathed in a Cs+-rich sea water ([Cs+] = 423 mM)
Summary
Giant axons from the squid were injected with 1.5 Mcesium sulfate solutions containing the radioactive isotopes 42K and '34Cs. The data suggest that internal cesium ions inhibit the outward potassium movement occurring during an action potential. The extra potassium effluxes taking place during excitation appear to be reduced in the presence of cesium ions to values between 7 and 22 % of those expected in the absence of cesium inhibition. The cesium perfusion medium, first prolonged the action potential and led to membrane depolarization and eventual loss of excitability. The work cited shows that the squid axon membrane is relatively impermeable to cesium ions and that when present internally, cesium ions interfere with the outward movement of potassium ions. The purpose of this paper is to report the results obtained in cases in which both 4 2K and 134Cs efflux are measured at rest and when axons are giving long duration responses due to the presence of a high internal cesium concentration
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