Passive Ion Fluxes Research Articles

The Effect of Dio-9 on Photosynthesis and Ion Transport inNitella,Tolypella, andHydrodictyon

The effect of Dio-9 on photosynthesis and active and passive ion transport at the plasmalemma has been investigated in Nitella translucens, Tolypella intricata, and Hydrodictyon africanum. The active K influx and the coupled active Na efflux were more inhibited by this inhibitor of energy transfer in phosphorylation than was photosynthesis. The active CI influx, the associated downhill cation influxes, and passive ion fluxes were inhibited by Dio-9 to a smaller extent than was photo synthesis. CI influx in the light was often stimulated at concentrations of Dio-9 which inhibited photosynthesis. It was concluded that the active K influx and Na efflux require ATP, while the active CI influx does not. Possible links between the CI influx and electron transport and intermediates of photophosphorylation, and possible inhibition by Dio-9 of the transport ATPase in the plasmalemma are discussed.

Ion current and potential across membranes

Theoretical treatments of the membrane process in the steady state were presented by using the rate equation in the preceding paper (Kimizuka & Koketsu,1964). It was shown that the equation for the ion conductance and transport number were expressed as functions of the membrane permeability, the composition and the membrane potential. The transport numbers of ions to the membrane of frog's sartorius muscle in normal Ringer's solution were calculated according to the derived equation. The membrane potential calculated according to the Nernst equation by using the transport numbers and the equilibrium potentials of potassium, sodium and chloride ions was in agreement with the observed value. The membrane conductance was shown to be a function of the applied potential, by which the difference between the calculated membrane resistance at rest and the observed one, could be explained. The equation for the passive ion flux at rest was given as a function of the composition and the membrane permeability, and it was shown that the calculated passive movements of ions were consistent with the directions of the active transports. The equation for the resting potential, as well as the membrane conductance, were obtained for the case in which the external solution contains the bivalent ions. The prolonged action porential of the crustacean muscle fibers (Fatt & Ginsborg, 1958) in the presence of strontium ions could be expressed in terms of the derived equation, and the membrane permeabilities to the ions were evaluated according to the proposed relationships. It was shown that the current-voltage relation measured with the giant axon of loligo (Hodgkin, Huxley & Katz, 1952) could be expressed by the derived equations. The discussion for the states of the membrane was given in terms of the proposed theory. The current-voltage relation for the cable has also been derived.

A THEORY OF PASSIVE ION FLUX THROUGH AXON MEMBRANES.

WE propose a model to explain the passive flux of ions through the membranes of unmyelinated axons.

Rubidium and cesium fluxes in muscle as related to the membrane potential.

The reduction of membrane potential in frog sartorius muscle produced by rubidium and cesium ions has been studied over a wide concentration range and compared with depolarization occasioned by potassium ions. The constant field theory of passive flux has been used to predict the potential changes observed. The potential data suggest certain permeability coefficient ratios and these are compared with ratios obtained from flux data using radioactive tracers. The agreement of the flux with the potential data is good if account is taken of the inhibition of potassium flux which occurs in the presence of rubidium and cesium ions. A high temperature dependence has been observed for cesium influx (Q(10) = 2.5) which is correlated with the observation that cesium ions depolarize very little at low temperatures. The observations suggest that cesium ions behave more like sodium ions at low temperatures and more like potassium ions at room temperature with respect to their effect on the muscle cell resting potential. The constant field theory of passive ion flux appears to be in general agreement with the experimental results observed if account is taken of the dependence of permeability coefficients on the concentrations of ions used and of possible interactions between the permeabilities of ions.