Microelectrode techniques were used on epidermal peels of Avicennia ge
rminans to characterize functional 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 velo
city and magnitude of these transcellular depolarizations varied: K+ >
Na+ > Mg++ >> Cl-. Increasing the pH of the incubation medium from 5.
5 to 7.0 reduced both the rate and the magnitude of voltage decrease w
hen 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 i
n K+ concentration was partially blocked by tetraethyl ammonium chlori
de (TEA) but not in Na+, Niflumic acid reduced the magnitude of the tr
anscellular 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 Bur occurred across epi
dermal peels of, A. germinans in regions where there were salt glands.
Salt secretion is best explained by a modified chemiosmotic hypothesi
s where cation channels and!or permeases work in concert with the elec
trochemical proton gradient generated by the plasma membrane H+/ATPase
.