The role of the rectum in osmoregulation and the potential effect of renoguanylin on SLC26a6 transport activity in the Gulf toadfish (Opsanus beta)

Ruhr, Ilan M.; Takei, Yoshio; Grosell, Martin

Abstract

The role of the rectum in osmo- regulation and the potential effect of renoguanylin on SLC26a6 transport activity in the Gulf toadfish (Opsanus beta). Am J Physiol Regul Integr Comp Physiol 311: R179 –R191, 2016. First published March 30, 2016; doi:10.1152/ajpregu.00033.2016.—Teleosts living in seawater continually absorb water across the intestine to compen- sate for branchial water loss to the environment. The present study reveals that the Gulf toadfish (Opsanus beta) rectum plays a compa- rable role to the posterior intestine in ion and water absorption. However, the posterior intestine appears to rely more on SLC26a6 (a HCO3 /Cl antiporter) and the rectum appears to rely on NKCC2 (SLC12a1) for the purposes of solute-coupled water absorption. The present study also demonstrates that the rectum responds to renogua- nylin (RGN), a member of the guanylin family of peptides that alters the normal osmoregulatory processes of the distal intestine, by inhib- ited water absorption. RGN decreases rectal water absorption more greatly than in the posterior intestine and leads to net Na and Cl secretion, and a reversal of the absorptive short-circuit current (ISC ). It is hypothesized that maintaining a larger fluid volume within the distal segments of intestinal tract facilitates the removal of CaCO3 precipitates and other solids from the intestine. Indeed, the expression of the components of the Cl-secretory response, apical CFTR, and basolateral NKCC1 (SLC12a2), are upregulated in the rectum of the Gulf toadfish after 96 h in 60 ppt, an exposure that increases CaCO3 precipitate formation relative to 35 ppt. Moreover, the downstream intracellular effects of RGN appear to directly inhibit ion absorption by NKCC2 and anion exchange by SLC26a6. Overall, the present findings elucidate key electrophysiological differences between the posterior intestine and rectum of Gulf toadfish and the potent regula- tory role renoguanylin plays in osmoregulation.

• Journal Article Type: Article
• Acceptance Date: Mar 28, 2016
• Online Publication Date: Mar 30, 2016
• Publication Date: 2016
• Deposit Date: Jun 11, 2025
• Journal: American Journal of Physiology - Regulatory Integrative and Comparative Physiology
• Print ISSN: 0363-6119
• Electronic ISSN: 1522-1490
• Publisher: American Physiological Society
• Peer Reviewed: Peer Reviewed
• Volume: 311
• Issue: 1
• Pages: R179-R191
• DOI: https://doi.org/10.1152/ajpregu.00033.2016