Taurine and cell volume maintenance in the shark rectal gland: cellular fluxes and kinetics.
Tissue slices of shark rectal gland are studied to examine the kinetics of the cellular fluxes of taurine, a major intracellular osmolyte in this organ. Maintenance of high steady-state cell taurine (50 mM) is achieved by a ouabain-sensitive active Na+-dependent uptake process and a relatively slow efflux. Uptake kinetics are described by two saturable taurine transport components (high-affinity, Km 60 microM; and low-affinity, Km 9 mM). [14C]Taurine uptake is enhanced by external Cl-, inhibited by beta-alanine and unaffected by inhibitors of the Na+/K+/2Cl- co-transport system. Two cellular efflux components of taurine are documented. Incubation of slices in p-chloromercuribenzene sulfonate (1 mM) reduces taurine uptake, increases efflux of taurine and induces cell swelling. Studies of efflux in isotonic media with various cation and anion substitutions demonstrate that high-K+ markedly enhances taurine efflux irrespective of cell volume changes (i.e. membrane stretching is not involved). Moreover, iso-osmotic cell swelling induced in media containing propionate is not associated with enhanced efflux of taurine from the cells. It is suggested that external K+ exerts a specific effect on the cytoplasmic membrane to increase its permeability to taurine.
Ziyadeh
F N
FN
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104.
Feldman
G M
GM
Booz
G W
GW
Kleinzeller
A
A
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000378:metabolism; D002794:Choline / Q000378:metabolism; D046508:Culture Techniques; D004284:Dogfish; D005942:Gluconates / Q000378:metabolism; D007513:Isethionic Acid / Q000494:pharmacology; D007700:Kinetics; D008094:Lithium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011422:Propionates / Q000378:metabolism / Q000494:pharmacology; D012491:Salt Gland / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013654:Taurine / Q000378:metabolism*; D015091:beta-Alanine / Q000494:pharmacology
D002712:Chlorides; D005942:Gluconates; D011422:Propionates; D015091:beta-Alanine; D013654:Taurine; D002731:4-Chloromercuribenzenesulfonate; D007513:Isethionic Acid; D008094:Lithium; D012964:Sodium; D002794:Choline; D011188:Potassium