The rapid non-genomic effects of 17-β-oestradiol (E2) on transepithelial bumetanide-sensitive Cl– secretion(ICl) and cell signalling were compared between male and female rat isolated distal colon mounted in Ussing chambers. The rats were humanely killed by cervical dislocation. The data are presented as means ± S.E.M. and were compared using Student’s paired t test.
E2 (100 nM) inhibited basal ICl by 60 ± 4 % (n = 8, P < 0.01) and prevented chloride secretion in response to heat-stable enterotoxin, cholera toxin, carbachol or forskolin. The rapid time course of the anti-secretory effect of E2 (< 5 min) and the insensitivity to cycloheximide, actinomycin or tamoxifen suggest the participation of a novel receptor. The anti-secretory effect of E2 was associated with a stimulation of PKCδ activity of 50 ± 4 % (n = 18, P < 0.01). E2 also produced an increase in adenyl cyclase and cyclic AMP activity and a transient rise in intracellular Ca2+ from 280 ± 10 to 415 ± 12 nM, (n = 8, P < 0.01), followed by an enhanced Na+/H+ exchange activity (measured as amiloride-sensitive pHi recovery rate in BCECF-loaded crypts). These latter signalling effects were dependent on the prior activation of PKCδ. The effects of E2 on chloride secretion and cell signalling were observed only in tissues of female origin and were absent from the male. Inhibition of the PKCδ isoform by rottlerin or chelation of intracellular Ca2+ with BAPTAM prevented the anti-secretory effects of E2. In nystatin-perforated luminal membrane preparations, E2 inhibited a chromanol 293B-sensitive basolateral K+ current which was insensitive to charybdotoxin, apamin, tolbutamide or verapamil.
In conclusion, E2 inhibits chloride secretion in female distal colon via a PKA signalling pathway and targets a basolateral membrane K+ channel of type KCNQ1/KCNE3.
This work was funded by a Wellcome Trust Programme Grant 060809/Z/00/Z.