Bioelectric Effects of Ions Microinjected Into the Giant Axon of Loligo

Abstract

1. A technique is described for recording the bioelectric activity of the squid giant axon during and following alteration of the internal axonal composition with respect to ions or other substances. 2. Experimental evidence indicates that the technique as described is capable of measuring changes in local bioelectric activity with an accuracy of 10 to 15 per cent or higher. 3. Alterations of the internal K+ or Cl- concentrations do not cause the change in resting potential expected on the basis of a Donnan mechanism. 4. The general effect of microinjection of K+ Rb+, Na+, Li+, Ba++, Ca++, Mg++, or Sr++ is to cause decrease in spike amplitude, followed by propagation block. 5. The resting potential decreases when the amplitude of the spike becomes low and block is incipient. 6. The decrease in resting potential and spike amplitude may be confined to the immediate vicinity of the injection. 7. At block, the resting potential decreases up to 50 per cent, but injection of small quantities of divalent cations may cause much larger localized depolarization. 8. The blocking effectiveness of K+, Na+, and Ca++ expressed as reciprocals of the relative amounts needed to cause block is approximately 1:5:100. Rb+ has the same low effectiveness as does K+. Li+ resembles Na+. Ba++ and Mg++ are approximately as effective as Ca++. 9. Microinjection of Na+ may cause marked prolongation of the spike at the injection site as well as decrease in its amplitude. 10. The anions used (Cl-, HCO3-, NO3-, SO4-, aspartate, and glutamate) do not seem to exert specific effects. 11. A tentative explanation is offered for the insensitivity of the resting potential to changes in the axonal ionic composition. 12. New data are presented on the range of variation, in a large sample, of the magnitude of the resting potential and spike amplitude.

Electrophysiology of Supramedullary Neurons in Spheroides maculatus

“…Since the microelectrodes used in this work had relatively large tips, spurious potentials reported to occur with very fine tipped microcapillaries (1) were probably negligible. This had also been found in previous work with electrodes of similar size used for impaling and injecting squid giant axons (23). T h e smaller values were probably due to DIRECTLY EVOKF.D SPreES An intracellularly applied depolarizing current produced a spike which will be designated as " d i r e c t " (Fig.…”

The electrical properties of the motoneurone membrane

“…It is, nevertheless, clear from the effects produced onthe inhibitory post-synaptic potential, which will be considered in a later paper, that after an injection of Cl-, Br-or NO the injected ions proceeded to leave the neurone so that it was half-way back to its original condition in about 20 sec. The small depolarization produced by the injection of these anions suggests that the ionic currents contributed by the outward diffusion of such ions were small compared to the total steadystate ionic currents across the membrane, including that due to the active transfer of ions (Ussing, 1949;Grundfest, Kao & Altamirano, 1954). The injection of sulphate and phosphate in large amounts (order of 50 p-equiv) often appreciably reduced the resting potential and recovery was incomplete or absent, which may be attributed to an uptake of water and swelling of the cell as the total internal content of non-penetrating salts was increased.…”

“…With pumps playing a prominent part in ionic movements, the membrane potential may not be determined solely by diffusion across the membrane of the various species of ions (cf. Grundfest, Kao & Altamirano, 1954). If the movement of different ions by the pump was so balanced that there was no net transfer of charge, the membrane potential would be determined by the concentrations of, and passive permeabilities toward, all the different species of ions on the two sides of the membrane.…”

Dependence of resting and action potentials on internal potassium in perfused squid giant axons

“…This was achieved by soaking tissues in ion-free or hypotonic solutions (Tobias, 1950; Adrian, 1956;Stephenson, 1957;Koketsu & Kimura, 1960), or by injecting solutions intracellularly (Grundfest, Kao & Altamirano, 1954;Gibbs & Johnson, 1962). However, these methods did not allow one to change drastically intracellular ionic compositions at will.…”