17beta-oestradiol acutely regulates Cl- secretion in rat distal colonic epithelium.

In this study we used the short circuit current (ISC) technique to measure the non-genomic effects of the female sex steroid 17beta-oestradiol (E2) on electrogenic transepithelial ion transport in rat distal colonic epithelium. Basal ISC was largely composed of a transepithelial Cl- secretory component with minimal electrogenic Na+ movement. E2 (1-100 nM) caused a significant decrease in basal ISC after 15 min. In addition, pre-treating colonic epithelial tissues with E2 (0.1-100 nM) for 10 min significantly reduced forskolin (20 microM)-induced Cl- secretion. E2 also down-regulated Cl- secretion which was pre-stimulated by forskolin. Cl- secretory responses to the Ca2+-dependent secretagogue carbachol (10 microM) were also significantly reduced in the presence of E2 (10- 100 nM). However, E2 had no effect on amiloride-sensitive Na+ absorption. The rapid anti-secretory effect of E2 was abolished in the presence of the intracellular Ca2+ chelator BAPTA (50 microM) or the protein kinase C (PKC) inhibitor chelerythrine chloride (1 microM). However, in the presence of the nuclear oestrogen receptor antagonist tamoxifen (10 microM), E2 still produced an inhibition of Cl- secretion. Testosterone, progesterone and 17alpha-oestradiol had no significant effect on colonic Cl- secretion. Also, E2 (100 nM) did not alter Cl- secretion in colonic epithelia isolated from male rats. We conclude that E2 inhibits colonic Cl- secretion via a non-genomic pathway that involves intracellular Ca2+ and PKC. It is possible that this gender-specific mechanism contributes to the salt and water retention associated with high E2 states.

Rapid non-genomic activation of cytosolic cyclic AMP-dependent protein kinase activity and [Ca(2+)](i) by 17beta-oestradiol in female rat distal colon.

1. In this study, the effect of 17beta-oestradiol on adenosine 3' : 5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase (PKA) activity was investigated. 2. Rapid (within 15 min) activation of basal PKA activity was observed in cytosolic fractions by 17beta-oestradiol but not by 17alpha-oestradiol, progesterone or testosterone. This stimulation was abolished by the specific PKA inhibitor PKI but not by the classical oestrogen receptor antagonist tamoxifen. 3. 17beta-Oestradiol did not stimulate basal PKA activity in membrane fractions or in cytosolic fractions from male rats. 4. The increase in cytosolic PKA activity was indirect as (i) it was inhibited by the adenylyl cyclase inhibitor SQ22536, (ii) it was mimicked by forskolin and (iii) 17beta-oestradiol did not cause a stimulation of basal PKA activity in either type I or type II commercially available PKA holoenzymes. 5. Protein kinase Cdelta (PKCdelta) was directly activated by 17beta-oestradiol. The specific PKC inhibitor, bisindolylmaleimide I (GF 109203X), abolished the 6. 17beta-oestradiol-induced PKA activation. 17beta-Oestradiol stimulate an increase in free intracellular calcium ion concentration ([Ca(2+)](i)) in isolated female but not male rat colonic crypts. This was inhibited by verapamil, nifedipine and zero extracellular [Ca(2+)] but unaffected by tamoxifen. 17alpha-Oestradiol, testosterone and progesterone failed to increase [Ca(2+)](i). 7. PKC and PKA inhibitors abolished the 17beta-oestradiol-induced increase in [Ca(2+)](i). 8. These results demonstrate the existence of a novel 17beta-oestradiol-specific PKA and Ca(2+) signalling pathway, which is both sex steroid- and gender-specific, in rat distal colonic epithelium.