AJP - Cell Physiology, Vol 255, Issue 2 C246-C251, Copyright © 1988 by American Physiological Society
8-BrcAMP does not affect Na-K-2Cl cotransport in winter flounder intestine
M. C. Rao and N. T. Nash
Department of Physiology and Biophysics, University of Illinois College of Medicine, Chicago 60612.
The flounder intestinal epithelium possesses luminal Na-K-2Cl cotransport
and K secretory mechanisms that account for the short-circuit current (Isc)
across the tissue. This epithelium is also highly cation selective.
Bumetanide or 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP)
completely inhibit Isc, Na-K-2Cl cotransport, and K secretion, whereas
8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) inhibits K
secretion, partially inhibits Isc, and greatly increases Cl permeability.
Although the direct effects of adenosine 3',5'-cyclic monophosphate (cAMP)
on other Na-K-2Cl cotransport systems have been examined, the effects of
8-BrcAMP on flounder intestinal Na-K-2Cl cotransport have not been directly
measured. In this study, the effects of 8-BrcAMP and bumetanide, either
alone or in combination, on the influx (initial rates of uptake) of Cl, Rb,
and Na across the luminal surface of the flounder intestine were examined.
Bumetanide significantly inhibited Na (50%), Cl, and Rb influx (70% each).
In contrast, 8-BrcAMP significantly increased Cl influx in the presence or
absence of bumetanide and thereby did not effect the bumetanide-sensitive
Cl influx. The nucleotide neither altered bumetanide-sensitive Rb influx
nor net transpithelial Na absorption measured under short-circuit
conditions but caused a 51-60% decrease in Isc. Measurements of
bumetanide-sensitive Na influx exhibited large experimental variability but
showed no statistically significant effects of 8-BrcAMP. Prostaglandin E1
(PGE1, 10 microM) and forskolin (10 microM) but not atrial natriuretic
factor (1 microM) increased flounder intestinal [cAMP] 200 and 237%,
respectively, and, like 8-BrcAMP, increased tissue conductance.(ABSTRACT
TRUNCATED AT 250 WORDS)
