Transepithelial transport and cell volume control in proximal renal tubules from the teleost Carassius auratus

Abstract

The objective of this work was to study cell volume regulation and transepithelial transport in renal proximal tubules. A modified stop-flow technique in in vitro perfused renal proximal tubules of Carassius auratus was used. The rate of luminal fluid absorption and the epithelial thickness were measured. Isosmotic Na+ removal from the tubule lumen or addition of the Na+/glucose co-transport blocker phloridzin (0.5 mM) to the lumen inhibited fluid absorption. Only minor effects on luminal absorption were observed following: (1) addition of the K+ channel inhibitor BaCl2 (1 mM); (2) addition of the Cl- channel inhibitor MK-196 (1 mM); (3) lowering bath and perfusate HCO3- in the presence of 0.1 mM acetazolamide; or (4) addition of the leukotriene-D4 receptor antagonist L-660, 711 (20 microM). Isosmotic addition of 40 mM taurine to the bath inhibited the rate of fluid absorption. This effect could be partially overcome with the organic acid secretion inhibitors probenecid (1 mM) and bromcresol green (0.1 mM). Finally, administration of the 5-lipoxygenase antagonist ETH 615-139 (20 microM) caused a significant reduction in the rate of luminal absorption. In summary, tubular reabsorption is, in this preparation, closely linked to sodium reabsorption. In the absence of luminal amino acids most of this sodium uptake seems to occur in co-transport with glucose followed by osmotically obligated water. Eicosanoids from the 5-lipoxygenase pathway appear to regulate this process. Finally high concentrations of taurine in the bath opposed luminal fluid absorption, at least partially, by its secretion into the tubular lumen.

The Effects of Putative K+ Channel Blockers on Volume Regulation of Murine Spermatozoa1

“…Phlorizin is a sodium-dependent hexose transport inhibitor that blocks myo-inositol transport in murine oocytes [36]. However, this nonspecific blocker also inhibits water transport through the sodium-glucose cotransporter (SGLT1) expressed in Xenopus laevis [39] and fluid absorption by renal proximal tubules of the teleost Carassius auratus [40]. Thus, the finding that murine spermatozoa incubated in phlorizin were significantly smaller than the control may be due to the inability of water to enter the treated cell.…”

The impact of hypoxia on in vivo glucose uptake in a hypoglycemic fish,Myoxocephalus scorpius

“…There is evidence for sodium-dependent glucose transport in frog skeletal muscle (23) and several other fish tissues (20,34); therefore, its potential role in glucose accumulation cannot be ignored. Identifying the mechanisms underlying white muscle glucose handling will be important to the understanding of glucose regulation in teleost fish.…”

Influence of cell volume changes on protein synthesis in isolated hepatocytes of air-breathing walking catfish (Clarias batrachus)

“…Looking at the enormous importance of osmoregulation in fishes, some reports on this line are already available concerning the cell volume regulatory mechanism in red blood cells (Fugelli and Thoroed 1986;Motais et al 1991;Haynes and Goldstein 1993;Cossins et al 1994), renal cells (Kanli and Terreros 1997;Kanli and Norderhus 1998), intestinal cells (Lionetto et al 2001(Lionetto et al , 2002(Lionetto et al , 2005Trischitta et al 2004), and few reports in fish liver cells (Bianchini et al 1988;Ballatori and Boyer 1992;Fossat et al 1997;Espelt et al 2003). More recently, it has been demonstrated that the liver cells of air-breathing walking catfish (Clarias batrachus) possess an efficient volume regulatory mechanism, but remain in a partly swollen or shrunken state as long as they are exposed to anisotonicity (Goswami and Saha 2006).…”