AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 2 106-G113, Copyright © 1980 by American Physiological Society
Stimulus-permeability coupling in rat lacrimal gland
R. J. Parod and J. W. Putney Jr
Incubation of isolated cells wtih 10(-2) M ethylene
glycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid or cobalt inhibits
22Na and 45Ca uptake stimulated by carbachol. The artificial introduction
of Ca into the cytosol by the cation ionophore A23187 also initiates the
22Na uptake. Amiloride (10(-5) M) partially inhibits 22Na uptake induced by
carbachol, but has no effect on receptor-stimulated 45Ca uptake or 86Rb
release. Tetrodotoxin (TTX) has no effect on 22Na uptake stimulated by
carbachol, whereas methoxyverapamil (D 600) produces a small but
significant decrease in both 22Na and 45Ca uptake. This effect of D 600 may
be related to a block of receptor activation and not to a block of Ca
channel activation. Incubation in high K (56 mM) does not prevent the
change in membrane permeability to Ca, K, and Na initiated by carbachol. It
is concluded that carbachol stimulates the influx of Ca; the rise in the
cytosolic Ca concentration then couples receptor activation to a change in
membrane permeability to K and Na. The permeability mechanisms for Ca, K,
and Na that are activated by carbachol appear to be specific for each of
the three cations and appear to be dissimilar to permeability mechanisms in
excitable tissue that carry the same ions.
