Taurine transport by isolated flounder renal tubules

Abstract

Previous in vivo clearance studies (Schrock et al., '82) have revealed that taurine is secreted by marine fish kidneys. In the present study taurine secretion by the flounder (Pseudopleuronectes americanus) renal tubule was investigated by assaying the transport of 14C-taurine in vitro. Collections from isolated fluid-secreting flounder tubules confirmed the presence of a tubular mechanism for taurine secretion. The flounder renal tubule concentrated taurine in the lumen at a lumen/bath ratio of 25, with the movement across the peritubular membrane identified as the concentrating step of taurine transport. Studies with teased flounder renal tubules identified transport as Na+ and C1- dependent. Taurine transport was inhibited by beta alanine, gamma-aminobutyric acid, and hypotaurine. In a study of the hormonal control of taurine transport, only the adrenal steroid dexamethasone stimulated taurine uptake by the flounder renal tubules. Transport was not affected by the second messengers adenosine 3'5'-cyclic monophosphate, guanosine 3'5'-cyclic monophosphate, adenosine, or Ca++ ionophore (A12384).

Taurine behaves as an osmolyte in Madin-Darby canine kidney cells. Protection by polarized, regulated transport of taurine.

“…The substitution of choline for sodium or gluconate-for CPalmost completely inhibited taurine uptake on both surfaces. Also, the taurine transporter at both surfaces was like those described in other tissues (9,10,(13)(14)(15) in that taurine uptake was inhibited by #-amino acids, hypotaurine and #l-alanine, but not by an a-amino acid, L-alanine. We did not determine the apparent affinity of the transporter for other fl-amino acids compared to its affinity for taurine.…”

“…Plasma taurine is -50 MM (8). Taurine is accumulated during hypertonicity or released during shift to lower osmolarity by tissues in fish (14,21,27), by Ehrlich ascites tumor cells (15,17), and in most (23)(24)(25), but not all (26) studies of rat brain. In this study we found that taurine uptake and release by MDCK cells was regulated by medium osmolarity.…”

“…High intracellular taurine concentrations in tissues reported to have limited capacity for taurine biogenesis (7) indicate that taurine is probably taken up against a concentration gradient from extracellular fluid where its concentration is 50,uM (8). Na+-dependent taurine transport has been well characterized in many tissues (9)(10)(11)(12)(13)(14)(15)(16). The transporter has a far higher affinity for a-amino acids than for a-amino acids (6), and is unusual in that chloride is also required (13,(17)(18)(19)(20).…”

“…The hypertonic brains also contained some other well-established osmolytes (25,26). When fish were shifted to a hypoosmotic environment (14,27,28), they excreted taurine in their urine, reflecting taurine release from tissues (29). Ehrlich ascites tumor cells released taurine when shifted to a hypoosmotic solution (15,17).…”

Taurine and Osmoregulation. IV. Cerebral Taurine Transport Is Increased in Rats with Hypernatremic Dehydration

“…It has been assumed that during cerebral cell volume regulation, fluctuations in the cytosolic levels of osmolytes are mediated by release and reuptake of osmolytes into subcellular sequestration sites (2,7). However, recent data in flounder erythrocytes (38), skate renal tubules (23), mammalian brain cells (35,37,39), and renal medullary cells (40)(41)(42) indicate that regulation of transmembrane flux of osmoprotective molecules is a critical component of cell volume regulation during exposure to anisotonic media. Oral administration of taurine analogues to rats before induction of hypernatremic dehydration supplements the cerebral pool of osmolytes and confers protection against cell shrinkage during hypernatremia (8).…”