Cystic fibrosis transmembrane conductance regulator mediates the cyclic adenosine monophosphate-induced fluid secretion but not the inhibition of resorption in mouse gallbladder epithelium

✍ Scribed by R H Peters; J H van Doorninck; P J French; R Ratcliff; M J Evans; W H Colledge; J Bijman; B J Scholte

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 728 KB
• Volume: 25
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.510250203

✦ Synopsis

CFTR is an anion channel, localized in active form at the We have studied the physiological role of the cystic apical plasma membrane of polarized epithelial cells. The fibrosis (CF) gene product (cystic fibrosis transmemchannel is activated by phosphorylation of the intracellular brane conductance regulator [CFTR]) in gallbladder epidomain by protein kinases. CFTR is thought to play a role thelium using a knockout mouse model for CF. We found in net fluid transport across epithelia, 7 but direct evidence that normal mouse gallbladder epithelium expresses for such a role is limited to mouse intestine 9 and cultured functional CFTR as shown by reverse-transcription airway epithelium. 11 The involvement of CFTR in plasma polymerase chain reaction (RT-PCR) analysis and Ussmembrane recycling and acidification of intracellular vesing chamber experiments. Gallbladders from Cftr 0/0 icles 14 has also been suggested. Recent evidence shows that mice were structurally intact as shown by microscopic CFTR can influence the activity of a parallel chloride conducand physiological parameters but lacked the cyclic adentance, possibly through a regulated adenosine triphosphate osine monophosphate (cAMP)-induced chloride current efflux function; however, the physiological significance of this observed in normal gallbladders. In fluid transport meamechanism remains to be established. 15 surements, normal and Cftr 0/0 gallbladders were

In the liver, CFTR messenger RNA (mRNA) and protein equally active in basal resorption. The addition of forare expressed in bile duct epithelial cells, as shown for rat 16 skolin, which activates CFTR anion channel activity and humans. 17, In isolated rat bile duct epithelial cells, a through the cAMP system, resulted in net fluid secretion cyclic adenosine monophosphate (cAMP)-dependent chloride in normal gallbladders. In contrast, Cftr 0/0 gallbladconductance, with properties typical of CFTR, was obders were unable to secrete fluid while a complete inhiserved. 19 In mouse 20,21 and human gallbladder epithebition of resorption by forskolin was observed. We conlium, CFTR expression and chloride transport activity has clude that, in normal mouse gallbladder epithelium, been reported. Similarly, in Necturus gallbladder, a cAMP-cAMP-induced fluid secretion involves simultaneous independent homologue of CFTR was described. [24][25] However, hibition of apical sodium chloride resorption and activathe relationship between the complex and variable hepatic tion of CFTR. Our data support the hypothesis that gallabnormalities in CF patients and the primary function of bladder disease in CF is at least in part caused by a CFTR, i.e., chloride transport at the apical epithelial memdeficient secretory response to the endogenous cAMPbrane, is not resolved now. By analogy with its role in other linked hormones VIP and secretin. (HEPATOLOGY tissues, CFTR in biliary and gallbladder tissue is likely to be 1997;25:270-277.)

involved in regulated isosmotic fluid transport, which determines bile output and composition. However, this has not Hepatobiliary abnormalities are quite common and severe been shown directly. The mechanism of fluid resorption in the in cystic fibrosis (CF) patients, although lung disease is still gallbladder has been described in the literature (Fig. ). the main cause of mortality and morbidity in CF. 1 These Inhibition and even reversal of fluid resorption has been obabnormalities include the obstruction of intrahepatic biliary served upon b-adrenergic stimulation in several species. ducts and subsequent hepatic fibrosis, 2,3 as well as gallblad-Using a CF mouse model, we show here that CFTR is reder dysmorphia and frequent gallstones. One may presume quired for cAMP-induced isosmotic fluid secretion in the inthat, as the treatment of lung disease in CF improves, hepatic tact gallbladder, and that cAMP-mediated inhibition of redisease will become even more manifest. The primary defect sorption is independent of CFTR in this tissue (Fig. ). in CF is related to mutations in a gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR).

MATERIALS AND METHODS

Animals.

All animal experiments were performed according to the guidelines issued by the Dutch government concerning animal care. A colony of mice with a lesion in the CFTR gene resulting in Abbreviations: CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance complete loss of function 29 was bred under pathogen-free conditions regulator; mRNA, messenger RNA; cAMP, cyclic adenosine monophosphate; PD, potential difference; RT-PCR, reverse-transcription polymerase chain reaction; EIPA, ethyl-isopropyl in our transgenic unit. The genotype of each individual animal was amiloride; Isc, short circuit current.

tested by Southern blotting of tail DNA. The Cftr 0/0 animals in our From 1 Cell Biology, Erasmus University, the Netherlands; and 2 Wellcome/CRC, Camfacility display less severe runting and mortality caused by intestinal bridge, England. obstruction than initially reported for the Cambridge colony. This is