Am. J. Respir. Cell Mol. Biol., Vol 10, No. 1, Jan 1994, 106-112.
Tannin inhibits cAMP pathways in bovine airway epithelium
MM Cloutier, L Guernsey and RI Sha'afi
Department of Pediatrics, University of Connecticut Health Center, Farmington 06030.
Tannin, isolated from aqueous extracts of cotton bracts, inhibits chloride
secretion in airway epithelial cells. The effect of tannin on the
epinephrine- and bradykinin-stimulated rise in intracellular free calcium
and cyclic adenosine monophosphate (cAMP) was examined using bovine
tracheal epithelial cells in suspension and culture. Basal intracellular
calcium levels were 33 +/- 11 nM (mean +/- SEM, n = 54) and increased 13-
to 15-fold after addition of epinephrine (10(-6) M) or bradykinin (2 x
10(-6) M). Tannin pretreatment blunted the subsequent response to
epinephrine beginning at a tannin concentration of 10 micrograms/ml.
Pretreatment with 100 micrograms/ml tannin completely inhibited the rise in
intracellular free calcium in response to epinephrine but had no effect on
the calcium response to bradykinin. In the absence of tannin, both
bradykinin and epinephrine increased intracellular levels of cAMP. At a
tannin concentration of 10 micrograms/ml, tannin inhibited the rise in
intracellular cAMP in cells stimulated with either epinephrine or
bradykinin but had no effect on bradykinin-stimulated prostaglandin E2
release. Tannin alone (10 micrograms/ml) increased prostaglandin E2
release. In other studies, tannin inhibited epinephrine binding to airway
epithelial cells in a dose-dependent manner. R(o) decreased from 948 +/- 69
fmol/mg protein under control conditions (n = 4) to 587 +/- 131 fmol/mg
protein in the presence of 25 micrograms/ml tannin (n = 3). Tannin had no
effect upon the Kd for epinephrine binding (132 +/- 12 pM). Tannin had no
effect on bradykinin binding to airway epithelial cells.(ABSTRACT TRUNCATED
AT 250 WORDS)
