MODIFICATION OF NERVE AFTER-POTENTIAL AND REFRACTORY PERIOD BY CHANGES OF IONIC ENVIRONMENT: NEW CASES OF PHYSIOLOGICAL ANTAGONISM BETWEEN UNIVALENT AND BIVALENT CATIONS

Publisher Website
Google Scholar
Abstract
The effect of varying the ionic environment of the isolated sciatic nerve of Rana pipiens was studied by means of the cathode ray oscillograph. Increase of the K ion content to 3-10 times its concentration in Ringer''s solution de creases the magnitude of the after-potential relatively more than it decreases the height of the spike. The duration of the after-potential is reduced to 20-50[sigma]. In crease of the Ca ion content to 9-13 times its concentra tion in Ringer''s solution increases the magnitude of the after-potential up to as much as 4% of the spike- potential with no effect on, or a slight decrease of, the spike height. The rising-time of the after-potential is prolonged to 10-30[sigma], and the total duration is 200 to 300[sigma]. The activity of rubidium and ammonium ions resembles that of the K ion. The Na, Cs, and Li ions are very much less active. The activity of the Ba, Mg, and Sr ions resembles that of the Ca ion, though Ba is somewhat more active. The beryllium and Al ions had no effect on the after-potential. Anions (except Ca precipitants) have no effect on the after-potential. The time-relations of the spike are not affected by excess of either univalent or bivalent cations. Accompanying the known increase of irritability with excess of univalent cations, and its decrease with excess of bivalent cations, there occurs a prolongation of the absolute and relative refractory periods with univalent cations, and a shorten ing of the relative refractory period and apparently no change of the absolute refractory period with bivalent cations. Excess of the K ion removes the supernormal phase; excess of the Ca ion causes this phase to begin earlier and last later than in normal nerve. There is an extensive similarity between the changes produced in various nerve functions by cathodal polarization and by excess of univalent cations on the one hand, and by anodal polarization and by excess of bivalent cations on the other. The sensitivity of the after-potential to the cationic environment indicates that it is a membrane function. The experimental fact and this conclusion from it are discussed in relation to their bearing on the nature of after-potential.

This publication has 1 reference indexed in Scilit: