Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

8-2004

Committee Chair or Co-Chairs

Thomas W. Ecay Jr.

Committee Members

Robert Wondergem, Dennis M. Defoe, Brian P. Rowe, Barbara Turner, Antonio E. Rusinol

Abstract

The human colonic cell line T84, a model for studying epithelial chloride secretion and cystic fibrosis chloride channel (CFTR) function, was used to investigate the regulatory role of estrogens in transepithelial ion transport. Estrogens and other steroid hormones do not stimulate chloride secretion by themselves. However, 17 β-estradiol (17β-E2) rapidly (within seconds to minutes) potentiates carbachol- and thapsigargin-stimulated chloride secretion measured as short circuit current in voltage-clamped T84 monolayer cultures. The cholinergic agonist carbachol and the SR Ca2+ ATPase inhibitor thapsigargin stimulate chloride secretion by elevating intracellular calcium. 17α-estradiol, a stereoisomer that does not activate nuclear estrogen receptors, is equipotent with 17β-E2. Other non-estrogen steroids produce much less, if any, potentiation of calcium-stimulated chloride secretion. The estrogen receptor antagonist tamoxifen does not block 17β-E2 potentiation of calcium-stimulated chloride secretion, indicating that the classical estrogen receptors are not involved. Potentiation is greater when 17β-E2 is applied to the apical membrane than to the basolateral membrane. 17β-E2 effects on chloride secretion coincide with an increase in monolayer electrical conductance, which is consistent with activation of one or more ion channel species. Potentiation is not blocked by the chloride channel blockers DIDS and NPPB but is abolished by the PKA inhibitor H89, suggesting that 17β-E2 potentiation depends on the activity of CFTR but not other types of apical membrane chloride channels. 17β-E2 does not increase the activity of calcium-activated potassium channels in the basolateral membrane as measured in nystatin-permeabilized monolayers. 17β-E2 effects are not blocked by the MAP kinase kinase inhibitor PD 98059, or by the PKC inhibitor bisindoylmaleamide, suggesting that these signal transduction pathways are not involved. 17β-E2 potentiation requires extracellular Ca2+. Paradoxically, 17β-E2 reduces the rise in intracellular free Ca2+ levels in thapsigargin-stimulated T84 cells, as measured by fura-2 fluorescence. From my studies I conclude that 17β-E2 causes an increase in the sensitivity of T84 cells to calcium-elevating secretagogues. This effect may be due to nongenomic actions of 17β-E2 on CFTR function and/or the activity of store-operated calcium channels, which leads to a change in CFTR functional regulation.

Document Type

Dissertation - Open Access

Copyright

Copyright by the authors.

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