The Relative Roles of External Taurine Concentration and Medium Osmolality in the Regulation of Taurine Transport in LLC-PK1 and MDCK Cells

Abstract

Taurine is a l3-sulfonic amino acid that serves as a nutrient important for developing brain and retina and as an osmolyte in the medullary collecting duct. The activity of the taurine transport system is regulated by substrate supply and by the external osmolality; these two stimuli induce changes in taurine transport. Increased medium osmolality (500 mosmol) stimulates taurine uptake into MDCK cells but not LLC-PKI cells. The enhanced taurine uptake that occurs in response to hyperosmolality is localized primaril y to the basolateral surface of MOCK cells, whereas the adapti ve response to medium taurine concentration is expressed on both the apical and the basolateral surfaces of both cell lines. The response of MOCK cells to medium osmolality requires protein synthesis and RNA transcription and is expressed in the presence of microtubular toxins. When cell monolayers were loaded with taurine by incubation in hightaurine medium before increasing medium osmolality, the expected increase in taurine uptake was blunted. Similarly, increased external l3-alanin e (500 p,M) also prevented the anticipated increase in taurine accumulation in response to hypertonicity; aminoisobutyric acid and betaine (500 p,M) partially prevented the increase in taurine transport after hypertonicity, T aurine, a f3-sulfonic am ino aci d that is found in millimol ar intrac ellular concentrati ons in the kidney o f many mammali an sp eci es, is pos tulated to ha ve several ke y functions in th e kidney ; among these are th e fun cti on of a nutritional substrat e, as w ell as that of an osmolyt e (1) . T aurine is tran sported b y the ren al tubular cell b y a sodium-and chlo ride-depe ndent tran sporter, w hich ac cepts the f3-amino aci d taurine and stru ctural ana lo gs such as f3-alanine (2-5) .Received April 26, 1994; accepted September 20, 1994 whereas L-alanine had no effect. The concentration of taurine or structurally similar analogs in the external medium might modify the response of taurine accumulation after exposure to hypertonic medium, in that taurine-replete cells behave differently than taurine-depleted cells. These studies indicate that there are at least two distinct mechanisms involved in the regulation of taurine transport: external taurine concentration and medium osmolality, with taurine concentration seeming to be the predominant stimulus. Thus, the changes in cell taurine transport depend on the physiologic stimulus as well as the cell studied, a phenomenon that might be related to the renal tubular site of origin. The kidney taurine tran sp orter serves at least tw o im po rta nt function s: 1) to reab sorb filte red taurine as a nutrient (this occurs in the proximal tubule and has been shown to be fun cti on all y immature in the neon at al rat, to be regulated by dietary taurine intake, and to be abnormal in the hypertaurininur ic mouse model) and 2) to offe r protection to medullary coll ecting du ct cell s or to MDCK (M ad in-Darby canine kidne y) cells in response to increased external os mola lity by se r...

Effects of Taurine on Nitric Oxide and 3-Nitrotyrosine Levels in Spleen During Endotoxemia

“…The contribution of taurine transport dependens upon the expression level and regulation of a taurine transporter (TauT), but also upon taurine level in extracellular medium. Increased maximal veliocity of taurine transport and increased levels of TauT mRNA have been consistently reported in a great variety of cells exposed to a hypertonic medium [49,50]. In the present study, we found that taurine plus endotoxin administration increased levels of taurine more, and the maximal mean of taurine level was seen in the taurine?endotoxemia group.…”

Ionic and Amino Acid Regulation in Hard Clam (Meretrix lusoria) in Response to Salinity Challenges

“…Phylogenetic analysis showed that this transporter belonged to the clade of mollusks TAUT. The activity and mRNA expression of TAUT were demonstrated to be inhibited by exogenous taurine supplementation, but were not modulated by glycine, alanine, or glutamic acid (Uchida et al, 1992; Jones et al, 1995; Han et al, 1997, 1998; Bitoun and Tappaz, 2000a,b; Takeuchi et al, 2000, 2001; Inoue et al, 2008). As others bivalves, e.g., deep-sea mussel, Mediterranean blue mussel, and Pacific giant oyster, the TAUT expression was detected in gills and mantles in the hard clam (Hosoi et al, 2005, 2007; Inoue et al, 2008).…”

Interaction between the actions of taurine and angiotensin II

“…The natriuretic activity of taurine has been attributed to its osmoregulatory activity in the kidney, its modulation of atrial natriuretic factor secretion, and its putative regulation of vasopressin release (Dlouha and McBroom, 1986;Miyata et al, 1997;Mozaffari et al, 1997). It can also be attributed to the excretion of taurine, resulting in less reabsorption of Na ϩ and Cl Ϫ across the renal epithelium (Zelikovic et al, 1989;Jones et al, 1995). Thus, taurine can cause a net loss of sodium without eliciting an extracellular volume expansion.…”