Animals
Wild type and Cftr null mice on two different genetic backgrounds were used in this study. One group was congenic on the C57Bl/6 (B6) background, as previously described [21]. The other group was on a mixed background of about 95% B6 and 5% 129/Sv (129). The mice on the mixed background originated as part of a recently published study [20] as follows. Mice carrying a targeted mutation of the gastrin gene on a mixed B6/129 background [51] were bred for eight generations onto the B6 background. The gastrin(+/-) mice were then crossed for six generations with Cftr(+/-) mice congenic on the B6 background. A genome scan at this point showed that the mice were about 95% B6 and 5% 129 (see below). These mice were bred to obtain mice wild type for both gastrin alleles and either Cftr homozygous wild type [Cftr(+/+)] or Cftr homozygous null [Cftr(-/-)].
Mice were genotyped at 2 weeks of age by PCR as previously described [21]. Unless otherwise stated, mice were maintained on a complete elemental liquid diet (Peptamen; Nestle Deerfield, IL) to prevent intestinal obstruction that occurs in CF mice [52]. Wild type littermates were maintained on the same diet. In some experiments, 8 week old mice were transferred onto solid mouse chow instead of Peptamen, and survival was recorded. Mice with apparent distress were sacrificed and survival on chow was recorded as the following day. Male and female mice were used at 6–16 weeks of age. Mice were kept in a specific pathogen-free facility in barrier-top cages. All procedures were approved by the University of Kansas Medical Center IACUC.