Streaming potentials in gramicidin channels measured with ion-selective microelectrodes.
Streaming potentials have been measured for gramicidin channels with a new method employing ion-selective microelectrodes. It is shown that ideally ion-selective electrodes placed at the membrane surface record the true streaming potential. Using this method for ion concentrations below 100 mM, approximately seven water molecules are transported whenever a sodium, potassium, or cesium ion, passes through the channel. This new method confirms earlier measurements (Rosenberg, P.A., and A. Finkelstein. 1978. Interaction of ions and water in gramicidin A channels. J. Gen. Physiol. 72:327-340) in which the streaming potentials were calculated as the difference between electrical potentials measured in the presence of gramicidin and in the presence of the ion carriers valinomycin and nonactin.
Tripathi
S
S
Tata Institute of Fundamental Research, Mumbai, India. tripathi@tifrvax.tifr.res.in
Hladky
S B
SB
D000900:Anti-Bacterial Agents; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods; D006096:Gramicidin / Q000737:chemistry*; D007473:Ion Channels / Q000502:physiology*; D018942:Macrolides; D008564:Membrane Potentials / Q000502:physiology*; D008839:Microelectrodes; D008954:Models, Biological; D014634:Valinomycin
D000900:Anti-Bacterial Agents; D007473:Ion Channels; D018942:Macrolides; D006096:Gramicidin; D014634:Valinomycin; C050476:nonactin