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secretion in G551D
cystic fibrosis mutant mice
1 Ion Transport Unit, National Heart and Lung Institute, London SW3 6LR, United Kingdom; 2 Department for Molecular and Cellular Biology, University of Queensland, Brisbane 4072, Australia; and 3 Medical Research Council Human Genetics Unit, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
Some cystic
fibrosis transmembrane conductance regulator (CFTR) mutations, such as
G551D, result in a correctly localized Cl
channel at the cell
apical membrane, albeit with markedly reduced function. Patch-clamp
studies have indicated that both phosphatase inhibitors and
3-isobutyl-1-methylxanthine (IBMX) can induce
Cl
secretion through the
G551D mutant protein. We have now assessed whether these agents can
induce Cl
secretion in
cftrG551D mutant
mice. No induction of Cl
secretion was seen with the alkaline phosphatase inhibitors
bromotetramisole or levamisole in either the respiratory or intestinal
tracts of wild-type or
cftrG551D mice.
In contrast, in G551D intestinal tissues, IBMX was able to produce a
small CFTR-related secretory response [means ± SE: jejunum,
1.8 ± 0.9 µA/cm2,
n = 7; cecum, 3.7 ± 0.8 µA/cm2,
n = 7; rectum (in vivo),
1.9 ± 0.9 mV, n = 5]. This
was approximately one order of magnitude less than the wild-type
response to this agent and, in the cecum, was significantly greater
than that seen in null mice
(cftrUNC). In
the trachea, IBMX produced a transient
Cl
secretory response (37.3 ± 14.7 µA/cm2,
n = 6) of a magnitude similar to that
seen in wild-type mice (33.7 ± 4.7 µA/cm2,
n = 9). This response was also present
in null mice and therefore is likely to be independent of CFTR. No
effect of IBMX on Cl
secretion was seen in the nasal epithelium of
cftrG551D mice.
We conclude that IBMX is able to induce detectable levels of
CFTR-related Cl
secretion
in the intestinal tract but not the respiratory tract through the G551D
mutant protein.
mouse model; 3-isobutyl-1-methylxanthine; cystic fibrosis transmembrane conductance regulator
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