Summary Cystic fibrosis (CF) is characterized by abnormal epithelial Cl
– conductance (G
Cl). In vitro studies that have shown that cAMP regulation is an intrinsic property of the CF-affected G
Cl(CF-G
Cl) have been carried out previously on cultured secretory cells and on nonepithelial cells. Even though G
Cl in absorption is defective in CF, a clear demonstration of cAMP regulation of CF-G
Cl in a purely absorptive tissue is lacking. We studied the cAMP regulation of CF-G
Cl in the microperfused intact human reabsorptive
sweat duct. About 40% of the ducts responded to cAMP (responsive) while the remainder of the ducts did not. In responsive ducts, cAMP-elevating agents: -adrenergic agonist isoproterenol (IPR), CPT-cAMP, forskolin, theophylline or IBMX increased
G
tby about 2.3-fold (
n = no. of ducts = 8). Removal of media Cl
–, but not amiloride pretreatment (in the lumen), abolished the cAMP response, indicating exclusive activation of G
Cl. cAMP activated both apical and basolateral G
Cl. cAMP hyperpolarized gluconate: Cl
– (lumen: bath) transepithelial bionic potentials (
V
t=–20.3±5.2 mV, mean ±
se,
n=9) and transepithelial 3 1 luminal NaCl dilution diffusion potentials (
V
t=–8.8±2.9 mV,
n=5). cAMP activated basolateral G
Cl as indicated by increased bi-ionic (gluconate: Cl
–, bath: lumen) diffusion potentials (by about 12 mV). The voltage divider ratio in symmetric NaCl solutions increased by 60%. Compared to responsive ducts, nonresponsive ducts were characterized by smaller spontaneous transepithelial potentials in symmetrical Ringer's solution (
V
t=–6.9±0.8 mV,
n=24, nonresponsive vs. –19.4±1.8 mV,
n=22, responsive ducts) but larger bi-ionic potentials (–94±6 mV, n=35, nonresponsive vs. –65±5 mV,
n=17, responsive ducts) and dilution diffusion potentials (–40±5 mV,
n=11, nonresponsive vs. –29±3 mV,
n=7, responsive ducts). These results are consistent with an inherently (prestimulus) maximal activation of G
Cl in nonresponsive ducts and submaximal activation of G
Cl in responsive ducts. We conclude that cAMP activates CF-
G
Cl which is expressed and abnormal in both apical and basal membranes of this absorptive epithelium in CF.Abbreviations CF
cystic fibrosis
-
G
t
transepithelial conductance
-
V
b
electrical potential across the basolateral membrane
-
V
a
electrical potential across the apical membrane
-
V
t
transepithelial potential
-
V
b
transepithelial currentinduced voltage deflections across the basolateral membrane
-
V
a
transepithelial current-induced voltage deflections across the apical membrane
-
V
t
transepithelial current-induced voltage deflection across the epithelium
- VDR
voltage divider ratio
- G
Cl
transepithelial Cl
– conductance
- CF-G
Cl
cystic fibrosis-affected Cl
– conductance
- EMF
electromotive force
- IPR
isoproterenol
- IBMX
3-isobutyl-1-methylxanthine
- CPT-cAMP
chlorophenylthio-adenosine 3-5 cyclic monophosphate
- PGE
2
prostaglandin E
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