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Cell Biology International (2004) 28, 549–555 (Printed in Great Britain)

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Altered cyclic expression of epithelial Na⁺ channel subunits and cystic fibrosis transmembrane conductance regulator in mouse endometrium by a low sodium diet

Lai Ling Tsang, Ling Nga Chan and Hsiao Chang Chan^*

Epithelial Cell Biology Research Center, Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong

Abstract

Epithelial Na⁺ channel (ENaC) and cystic fibrosis transmembrane conductance (CFTR) have been shown to exhibit cyclic expression patterns in the uterus and demonstrated to play important roles in regulating uterine fluid absorption and secretion. The present study investigated the effect of a low Na⁺ diet on the cyclic expression of uterine ENaC subunits and CFTR in mice. Ten to 12 weeks old ICR mice with synchronized estrus cycle were fed with a low sodium diet for at least 2 weeks and the mRNA level of these ion channels was examined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). Functional channel activities in primary cultures of endometrial epithelia were assessed by the short-circuit current (Isc) technique. The characteristic cyclic expression of ENaC subunits throughout the estrus cycle remained unchanged but their expression levels towards the diestrus stage were drastically elevated. The cyclic expression pattern of CFTR was disrupted with suppressed expression throughout the cycle. Isc measurements showed that treatment of cultured endometrial epithelial cells with aldosterone, the major hormone expected to be elevated during the low sodium diet, resulted in prominent increase in ENaC channel activity. The altered cyclic expression of uterine ENaC and CFTR by a low sodium diet suggests that these ion channels may be affected by elevated circulating aldosterone, which may disrupt reproductive events in the uterus.

Key words: CFTR, ENaC, Endometrium, Low Na⁺ diet, Aldosterone, RT-PCR.

^*Corresponding author. Tel.: +852-2609-6839; fax: +852-2603-5022.

Received 30 December 2003/18 March 2004; accepted 26 April 2004