Interactions of Urea Transport and Synthesis in Hepatocytes of the Gulf Toadfish, Opsanus beta

نویسندگان

  • Patrick J. Walsh
  • Chris M. Wood
چکیده

Although urea transport is receiving increased attention in mammalian systems, little is known about urea transport in fish tissues. Recently, we identified a phloretin-sensitive urea efflux pathway in hepatocytes of gulf toadfish (Opsanus beta), a ureogenic teleost. The present study sought to further examine this transport system and its potential interrelation with metabolic urea production. The transport inhibitors phloretin and 1-(3,4-dichlorophenyl)-2-thiourea (DCPTU) both had substantial inhibitory effects on hepatocyte urea production rotes. These effects could be at least partially explained by inhibition of glutamate dehydrogenase (by phloretin) and argininosuccinate synthetase (by DCPTU) activities in vitro. Whereas phloretin substantially inhibited the efflux transport of urea, DCPTU did not. The metabolic effects of phloretin could be nearly eliminated by preparing hepatocytes in the absence of hyaluronidase, enabling its transport effects to be studied in isolation. In so doing we found that transporter inhibition did not lead to a substantial short-term buildup of intracellular urea concentration in hepatocytes. These results are discussed in the context of in vitro vs in vivo rates and pathways of urea transport or excretion. COMP BIOCHEM PHYSlOL 113B, 411-416, 1996.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Urea Transport by Hepatocytes and Red Blood Cells of Selected Elasmobranch and Teleost Fishes

Although urea transport is receiving increased attention in mammalian systems, very little is known about urea transport in fish tissues. This study examined mechanisms of urea transport in red blood cells and hepatocytes from the lesser spotted dogfish (Scyliorhinus canicula), Atlantic stingray (Dasyatis sabina), turbot (Scopthalmus maximus), redfish (Scianops ocellatus), gulf toadfish (Opsanu...

متن کامل

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

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 tha...

متن کامل

The regulatory role of glucocorticoid and mineralocorticoid receptors in pulsatile urea excretion of the gulf toadfish, Opsanus beta.

Gulf toadfish, Opsanus beta, are one among a group of unusual teleosts that excrete urea as their predominant nitrogen end product in response to stressful conditions. Under conditions of crowding or confinement, fasted toadfish excrete the majority of their nitrogen waste in large pulses of urea (>90% of total nitrogen) lasting up to 3 h. An earlier study demonstrated that cortisol has an inhi...

متن کامل

Lactate Uptake by Toadfish Hepatocytes: Passive Diffusion Is Sufficient

Mechanisms of hepatic lactate uptake were studied in the gulf toadfish, Opsanus beta by following the accumulation of [C]lactate by isolated hepatocytes in vitro. Uptake rates were linear for up to 5 s at external lactate concentrations of 1 and 20mmoll~'. 5-s uptake rates for several concentrations in the physiological range (i.e. 0-2-20mmoll") yielded a linear double reciprocal plot (l/v vs l...

متن کامل

Molecular characterization of a urea transporter in the gill of the gulf toadfish (Opsanus beta).

Urea excretion by the gulf toadfish (Opsanus beta) has been shown in previous studies to be a highly pulsatile facilitated transport, with excretion probably occurring at the gill. The present study reports the isolation of an 1800 base pair (kb) cDNA from toadfish gill with one open reading frame putatively encoding a 475-residue protein, the toadfish urea transporter (tUT). tUT, the first tel...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2003