Electrophysiology of the Salt Glands of Avicennia germinans.
Microelectrode techniques were used on epidermal peels of Avicennia germinans to characterize func- tional aspects of secretion in salt glands. Increasing the concentrations of K+, Na+, or Mg++ in the bath medium decreased the measured transcellular voltage and resistance. The velocity and magnitude of these transcellular depolarizations varied: K+>Na+>Mg++>>Cl-. Increasing the pH of the incubation me- dium from 5.5 to 7.0 reduced both the rate and the magnitude of voltage decrease when Na+ concentration was changed; tissue incubated at pH 8.0 did not form secretion droplets. Transcellular depolarizations resulting from concentration shifts of K+ from 10 to 100 mM were partially suppressed in the presence of La+++. The voltage decrease accompanying changes in K+ concentration was partially blocked by tetraethyl ammonium chloride (TEA) but not in Na+. Niflumic acid reduced the magnitude of the transcellular voltage with increased K+ concentration but did not affect the velocity. The small voltage decrease accompanying changes in Cl- concentration was not affected by either TEA or niflumic acid (NA). 2-4-Dinitrophenol (DNP), sodium azide, and vanadate markedly reduced the rapidity and the magnitude of voltage decrease accompanying increases in concentration of K+, Na+, or Mg++. Ion concentrations in secretion droplets indicated that a considerable cation flux occurred across epidermal peels of A. germinans in regions where there were salt glands. Salt secretion is best explained by a modified chemiosmotic hypothesis where cation channels and/or permeases work in concert with the electrochem- ical proton gradient generated by the plasma membrane H+/ATPase.
|Main Author:||Balsamo, Ronald.|
|Other Authors:||Adams, Michael., Thomson, William.|