Sexual dimorphism and oestrogen regulation of KCNE3 expression modulates the functional properties of KCNQ1 K⁺ channels.

Non-Technical Summary  High levels of oestrogen are known to cause fluid retention in fertile females. It is thought that the increase in body fluid volume is necessary for proper implantation of the fertilised egg in the uterus. We show that the activity of a potassium ion channel, which drives salt and water movement across the cell membranes of the intestine, is inhibited by oestrogen and this effect is only found in females and is maximal during the peak phase of oestrogen in the oestrous cycle (when fertilization and implantation occur). These findings help us to understand the molecular mechanisms underlying the fluid retention effects of oestrogen in health and the potential adverse effects this response may have in exacerbating disease where fluid secretion is compromised such as in cystic fibrosis (the so-called CF ‘gender gap’). Abstract  The KCNQ1 potassium channel associates with various KCNE ancillary subunits that drastically affect channel gating and pharmacology. Co-assembly with KCNE3 produces a current with nearly instantaneous activation, some time-dependent activation at very positive potentials, a linear current–voltage relationship and a 10-fold higher sensitivity to chromanol 293B. KCNQ1:KCNE3 channels are expressed in colonic crypts and mediate basolateral K+ recycling required for Cl− secretion. We have previously reported the female-specific anti-secretory effects of oestrogen via KCNQ1:KCNE3 channel inhibition in colonic crypts. This study was designed to determine whether sex and oestrogen regulate the expression and function of KCNQ1 and KCNE3 in rat distal colon. Colonic crypts were isolated from Sprague–Dawley rats and used for whole-cell patch-clamp and to extract total RNA and protein. Sheets of epithelium were used for short-circuit current recordings. KCNE1 and KCNE3 mRNA and protein abundance were significantly higher in male than female crypts. No expression of KCNE2 was found and no difference was observed in KCNQ1 expression between male and female (at oestrus) colonic crypts. Male crypts showed a 2.2-fold higher level of association of KCNQ1 and KCNE3 compared to female cells. In female colonic crypts, KCNQ1 and KCNE3 protein expression fluctuated throughout the oestrous cycle and 17β-oestradiol (E2 10 nm) produced a rapid (<15 min) dissociation of KCNQ1 and KCNE3 in female crypts only. Whole-cell K+ currents showed a linear current–voltage relationship in male crypts, while K+ currents in colonic crypts isolated from females displayed voltage-dependent outward rectification. Currents in isolated male crypts and epithelial sheets were 10-fold more sensitive to specific KCNQ1 inhibitors, such as chromanol 293B and HMR-1556, than in female. The effect of E2 on K+ currents mediated by KCNQ1 with or without different β-subunits was assayed from current–voltage relations elicited in CHO cells transfected with KCNQ1 and KCNE3 or KCNE1 cDNA. E2 (100 nm) reduced the currents mediated by the KCNQ1:KCNE3 potassium channel and had no effect on currents via KCNQ1:KCNE1 or KCNQ1 alone. Currents mediated by the complex formed by KCNQ1 and the mutant KCNE3-S82A β-subunit (mutation of the site for PKCδ-promoted phosphorylation and modulation of the activity of KCNE3) showed rapid run-down and insensitivity to E2. Together, these data suggest that oestrogen regulates the expression of the KCNE1 and KCNE3 and with it the gating and pharmacological properties of the K+ conductance required for Cl− secretion. The decreased association of the KCNQ1:KCNE3 channel complex promoted by oestrogen exposure underlies the molecular mechanism for the sexual dimorphism and oestrous cycle dependence of the anti-secretory actions of oestrogen in the intestine.