Cortisol-sensitive urea transport across the gill basolateral membrane of the gulf toadfish (Opsanus beta)

Tamara M. Rodela, Kathleen M. Gilmour, Patrick J. Walsh, M. Danielle McDonald

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Gulf toadfish (Opsanus beta) use a unique pulsatile urea excretion mechanism that allows urea to be voided in large pulses via the periodic insertion or activation of a branchial urea transporter. The precise cellular and subcellular location of the facilitated diffusion mechanism(s) remains unclear. An in vitro basolateral membrane vesicle (BLMV) preparation was used to test the hypothesis that urea movement across the gill basolateral membrane occurs through a cortisol-sensitive carrier-mediated mechanism. Toadfish BLMVs demonstrated two components of urea uptake: a linear element at high external urea concentrations, and a phloretin-sensitive saturable constituent (K m = 0.24 mmol/l; Vmax = 6.95 μmol·mg protein-1·h-1) at low urea concentrations (<1 mmol/l). BLMV urea transport in toadfish was unaffected by in vitro treatment with ouabain, N-ethylmaleimide, or the absence of sodium, conditions that are known to inhibit sodium-coupled and proton-coupled urea transport in vertebrates. Transport kinetics were temperature sensitive with a Q10 > 2, further suggestive of carrier-mediated processes. Our data provide evidence that a basolateral urea facilitated transporter accelerates the movement of urea between the plasma and gills to enable the pulsatile excretion of urea. Furthermore, in vivo infusion of cortisol caused a significant 4.3-fold reduction in BLMV urea transport capacity in lab-crowded fish, suggesting that cortisol inhibits the recruitment of urea transporters to the basolateral membrane, which may ultimately affect the size of the urea pulse event in gulf toadfish.

Original languageEnglish (US)
Pages (from-to)R313-R322
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number2
StatePublished - Aug 2009


  • Basolateral plasma membrane
  • Facilitated diffusion
  • Membrane vesicles
  • Phloretin
  • Urea permeability

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


Dive into the research topics of 'Cortisol-sensitive urea transport across the gill basolateral membrane of the gulf toadfish (Opsanus beta)'. Together they form a unique fingerprint.

Cite this