title: 22Na+ fluxes in thymic lymphocytes. I. Na+/Na+ and Na+/H+ exchange through an amiloride-insensitive pathway.
abstract: The Na+ transport pathways of normal rat thymocytes were investigated. Na+ conductance was found to be lower than K+ conductance, which is consistent with reported values of membrane potential. In contrast, the isotopically measured Na+ permeability was greater than 10-fold higher than that of K+, which indicates that most of the flux is electroneutral. Cotransport with Cl- (or K+ and Cl-) and countertransport with Ca2+ were ruled out by ion substitution experiments and use of inhibitors. Countertransport for Na+ or H+ through the amiloride-sensitive antiport accounts for only 15-20% of the resting influx. In the presence of amiloride, 22Na+ uptake was increased in Na+-loaded cells, which suggests the existence of Na+/Na+ countertransport. Cytoplasmic pH determinations using fluorescent probes indicated that under certain conditions this amiloride-resistant system will also exchange Na+ for H+, as evidenced by an internal Na+-dependent acidification is proportional to internal [Na+] but inversely related to extracellular [Na+]. Moreover, 22Na+ uptake is inhibited by increasing external [H+]. The results support the existence of a substantial amiloride-insensitive, electroneutral cation exchange system capable of transporting Na+ and H+.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D004553:Electric Conductivity; D006859:Hydrogen / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D008297:Male; D011188:Potassium / Q000378:metabolism; D011719:Pyrazines / Q000494:pharmacology*; D011868:Radioisotopes; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D012979:Sodium Radioisotopes; D013601:T-Lymphocytes / Q000378:metabolism*; D013696:Temperature; D013950:Thymus Gland / Q000166:cytology
chemical_list: D011719:Pyrazines; D011868:Radioisotopes; D012979:Sodium Radioisotopes; D000584:Amiloride; D006859:Hydrogen; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D011188:Potassium