Pathways of cycloleucine transport in killifish small intestine.

By using blocking concentrations of competitors, i.e., concentrations of other neutral amino acids that cause maximal inhibition, cycloleucine transport into slices or everted sacs of killifish (fundulus heteroclitus) small intestine could be partitioned into three pathways.

p-Aminohippuric acid transport into brush border vesicles isolated from flounder kidney.

p-Aminohippuric acid (PAH) transport was investigated in brush border vesicles isolated from renal proximal tubules of the winter flounder. Three characteristics of carrier-mediated transport were demonstrated: 1) unlabeled PAH inhibited the uptake of [3H]PAH; 2)[3H]PAH efflux from the vesicles was stimulated in the presence of unlabeled PAH in the extravesicular medium; and 3) PAH influx was inhibited by 2,4-dinitrophenol (DNP) and 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene (SITS). D-Glucose plus a sodium gradient stimulated PAH uptake, as did a K2SO4 gradient plus valinomycin, suggesting that PAH is transported as an anion.

Elasmobranch rectal gland cell: autoradiographic localization of [3H]ouabain-sensitive Na, K-ATPase in rectal gland of dogfish, Squalus acanthias.

Specific binding of radiolabeled inhibitor was employed to localize the Na-pump sites (Na,K-ATPase) in rectal gland epithelium, a NaCl-secreting osmoregulatory tissue which is particularly rich in pump sites. Slices of gland tissue from spiny dogfish were incubated in suitable [3H]ouabain-containing media and then prepared for Na,K-ATPase assay, measurement of radiolabel binding, or quantitative freeze-dry autoradiography at the light microscope level. Gross freezing or drying artifacts were excluded by comparison with additional aldehyde-fixed slices.

Excretion of phenol red by the Necturus kidney.

Phenol red (phenolsulfonphthalein, PSP) is thought to be secreted by proximal kidney tubules in all vertebrates. The present study examined PSP transport by the kidney of the salamander, Necturus maculosus. In Necturus kidneys perfused with oxygenated Ringer solution, the PSP/creatinine clearance ratio was unity.