Recording of the Ionic Efflux during Single Action Potentials in Nitellopsis Obtusa by Means of High‐Frequency Reflectometry

Abstract

The ionic efflux during a single action potential of the alga Nitellopsis obtusa was recorded by measuring the increase in conductivity of the extracellular fluid. The conductivity changes are reflected as variations in absorption of a high‐frequency field applied by a specially designed probe placed in the external medium close to the alga and connected to a high‐frequency reflectometer. The combined characteristics of probe/solution and reflectometer are given. Most experiments were performed on algae in distilled water, comparative experiments with lake water having shown that this arrangement does not introduce any significant changes in the activation processes studied. The possibility of dynamic recording of ionic fluxes is illustrated by oscillograph records showing the temporal relation between the ionic concentration change and the action potential; that the method is suitable for quantitative measurements is demonstrated by inkwriter records showing the stepwise increases in concentration caused by intermittent stimulation during hour‐long experiments. Quantitative data on the increments in ionic concentration associated with a single impulse, and on the total increase resulting from a number of stimuli, are presented and compared with chemical analyses showing the ions involved to be K+ and C1‐‐. Satisfactory correspondence was obtained between the values of the conductivity measurements, tentatively expressed as KC1 concentration, and the chemical analysis. The average values for the K+ efflux were 2 times 103 to 4 times 103 pmole/cm2. impulse; preliminary studies showed the C1– efflux to be of approximately the same order.

Membrane Electrical Behaviour in Nitellopsis Obtusa

“…and resistance of the plasmalemma and tonoplast and the efflux of chloride ions in the resting state of the cell and during the action potential have been measured. It is shown that the electrical behaviour of Nitellopsis obtusa is similar to that of Ohara corallina, Nitella translucens, .and the freshwater Nitellopsis obtusa used by Haapanen and Skoglund (1967), but certain aspects appear to be in conflict with conclusions reached by MacRobbie and Dainty (1958) from ionic flux studies with the brackish water Nitellopsis obtusa.…”

“…During this time, there will be a net efflux of chloride ions down the electrochemical gradient. In Ohara globularis (Gaffey and Mullins 1958), O. australis (Hope and Findlay, unpublished data) and freshwater N. obtusa (Haapanen and Skoglund 1967) the efflux of chloride is accompanied by an efflux of potassium ions. The values given by Haapanen and Skoglund for the amount of K + and CI-released by a single action potential, 2-4 X 104 pmole cm-2 impulse-I, are somewhat larger than those for the brackish water N. obtusa reported in this paper.…”

“…(Findlay 1959), Nitellaflexilis and Ohara braunii (Oda 1960), and Nitella translucens (Williams and Bradley 1968). (Gaffey and Mullins 1958), Nitella clavata (Mullins 1962), Ohara corallina (Hope and Findlay 1964), and Nitellopsis obtusa (Haapanen and Skoglund 1967) have shown that during the action potential there is a marked increase in efflux of potassium and chloride ions from the cell, from which it is inferred that the action potential results from a transient increase in the permeability of the plasmalemma to chloride ions.…”

Excitation ofCharaceae cell membranes as a result of activation of calcium and chloride channels

“…By the time our work began (1971) it was well-established that in the course of generation of algal action potentials, C1-ion outflux into external medium is enhanced [17]. This fact along with some other data led to the suggestion that C1-is the main currentcarrying ion [11,16,25] and that Ca 2 § ions control the value of transient chloride current [14]. It was also established that both membranes, plasmalemma and tonoplast, are excitable, and that excitation in the membranes proceeds simultaneously accompanying each other.…”

Spontaneous and induced changes in the membrane potential and resistance ofAcetabularia mediterranea

“…The time course of potential and resistance changes during a typical spike is generally slower than but otherwise resembles the changes observed during a Characean action potential (Findlay & Hope, 1964;Kishimoto, 1966b). It has been established that this action potential is caused by changes in membrane permeability to C1- (Gaffey & Mullins, 1958;Haapanen & Skoglund, 1967). Reuben etal.…”