Water absorption and bicarbonate secretion in the intestine of the sea bream are regulated by transmembrane and soluble adenylyl cyclase stimulation

J Comp Physiol B. 2012 Dec;182(8):1069-80. doi: 10.1007/s00360-012-0685-4. Epub 2012 Jun 30.


In the marine fish intestine luminal, HCO₃⁻ can remove divalent ions (calcium and magnesium) by precipitation in the form of carbonate aggregates. The process of epithelial HCO₃⁻ secretion is under endocrine control, therefore, in this study we aimed to characterize the involvement of transmembrane (tmACs) and soluble (sACs) adenylyl cyclases on the regulation of bicarbonate secretion (BCS) and water absorption in the intestine of the sea bream (Sparus aurata). We observed that all sections of sea bream intestine are able to secrete bicarbonate as measured by pH-Stat in Ussing chambers. In addition, gut sac preparations reveal net water absorption in all segments of the intestine, with significantly higher absorption rates in the anterior intestine that in the rectum. BCS and water absorption are positively correlated in all regions of the sea bream intestinal tract. Furthermore, stimulation of tmACs (10 μM FK + 500 μM IBMX) causes a significant decrease in BCS, bulk water absorption and short circuit current (Isc) in a region dependent manner. In turn, stimulation of sACs with elevated HCO₃⁻ results in a significant increase in BCS, and bulk water absorption in the anterior intestine, an action completely reversed by the sAC inhibitor KH7 (200 μM). Overall, the results reveal a functional relationship between BCS and water absorption in marine fish intestine and modulation by tmACs and sAC. In light of the present observations, it is hypothesized that the endocrine effects on intestinal BCS and water absorption mediated by tmACs are locally and reciprocally modulated by the action of sACs in the fish enterocyte, thus fine-tuning the process of carbonate aggregate production in the intestinal lumen.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclase Inhibitors
  • Adenylyl Cyclases / chemistry
  • Adenylyl Cyclases / metabolism*
  • Animals
  • Aquaculture
  • Bicarbonates / metabolism*
  • Biological Transport / drug effects
  • Enzyme Inhibitors / pharmacology
  • Fish Proteins / agonists*
  • Fish Proteins / antagonists & inhibitors
  • Fish Proteins / chemistry
  • Fish Proteins / metabolism
  • In Vitro Techniques
  • Intestinal Absorption / drug effects
  • Intestinal Mucosa / drug effects
  • Intestinal Mucosa / metabolism*
  • Intestines / drug effects
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / chemistry
  • Isoenzymes / metabolism
  • Membrane Proteins / agonists
  • Membrane Proteins / antagonists & inhibitors
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism
  • Membrane Transport Modulators / pharmacology
  • Organ Specificity
  • Phosphodiesterase Inhibitors / pharmacology
  • Sea Bream / physiology*
  • Seawater
  • Solubility
  • Water-Electrolyte Balance*


  • Adenylyl Cyclase Inhibitors
  • Bicarbonates
  • Enzyme Inhibitors
  • Fish Proteins
  • Isoenzymes
  • Membrane Proteins
  • Membrane Transport Modulators
  • Phosphodiesterase Inhibitors
  • Adenylyl Cyclases