Rapid Effects of Aldosterone on Sodium-Hydrogen Exchange in Isolated Colonic Crypts

Abstract

Aldosterone plays a central role in the homeostatic regulation of extracellular fluid volume by stimulating transepithelial electrolyte transport. These effects involve binding to an intracellular receptor, modification of genomic events and protein synthesis. Rapid cellular responses to steroid hormones have been observed in a variety of nonepithelial tissues. The term "nongenomic" has been proposed for these fast steroid responses since they are unaffected by inhibitors of protein synthesis. We hypothesized that colonic crypts, recently demonstrated to absorb fluid, would respond rapidly to aldosterone. Cytoplasmic pH changes in crypts loaded with a pH-sensitive, fluorescent dye (BCECF) were recorded with confocal laser imaging. An intracellular alkalization of colonic crypts was observed within one minute of aldosterone application that was inhibited by ethylisopropylamiloride or the absence of extracellular sodium, yet unaffected by inhibitors of protein synthesis. The genesis of this rapid and distinct steroid action involves a signal transduction pathway that involves G proteins, protein kinase C, and prostaglandins. We have identified, by real-time imaging, a nongenomic upregulation of sodium-hydrogen exchange in colonic crypts by aldosterone that occurs independent of the traditional receptor. This distinct, rapid onset effect of aldosterone on epithelial ion transport has major implications for our understanding of fluid and electrolyte homeostasis in health and disease.

Aldosterone Rapidly Activates Na⁺/H⁺ Exchange in M-1 Cortical Collecting Duct Cells via a PKC-MAPK Pathway

“…These rapid actions of aldosterone are believed to be mediated by an as yet unidentified plasma membrane receptor [2]. Spironolactone, the MR antagonist is unable to block a large proportion of the reported non-genomic responses, suggesting that the unknown receptor is unrelated to the classic MR [2, 4, 6, 10]. The non-genomic response has been identified in aldosterone-responsive epithelia such as distal colon [4, 5, 9, 10, 11], sweat gland [12], kidney [3, 6]and amphibian skin [13].…”

“…However, aldosterone can also induce rapid responses that occur in a timescale of seconds to minutes that do not require de novo protein synthesis [2]. These include regulation of intracellular pH (pH i ) [3, 4], intracellular Ca 2+ [5, 6], generation of inositol 1,4,5-triphosphate [7, 8]and activation of signal-transducing kinases such as protein kinase C (PKC) [9, 10]and extracellular signal-regulated kinase (ERK1/2) [3]. These rapid actions of aldosterone are believed to be mediated by an as yet unidentified plasma membrane receptor [2].…”

Acute Clinical Worsening after Steroid Administration in Cervical Myelitis May Reveal a Subdural Arteriovenous Fistula

“…In addition to anti-inflammatory effects, corticosteroids can also play a role in regulating water and mineral metabolism through their mineralocorticoid effects, causing fluid retention. This can compromise the already fragile venous return into the dural sac, leading to medullary hypoxia and further worsening the SDAVF symptoms [17]. Furthermore, steroids administered via an intravenous line placed in the upper extremity eventually drain via the cephalic veins into the brachiocephalic veins.…”

Isolation and gene expression profiling of intestinal epithelial cells: crypt isolation by calcium chelation from in vivo samples

“…EDTA (ethylenediaminetetraacetic acid) calcium chelation solution was prepared as described previously. 30 Briefly, the solution contained the following: 96 mM/L NaCl, 1.5 mM/L KCl, 10 mM HEPES/Tris, 27 mM NaEDTA, 45 mM/L Sorbitol, and 28 mM/L sucrose. All reagents were sourced from Sigma-Aldrich Co. (St Louis, MO, USA).…”