Regulation of Na+ and K+ contents in rat thymocytes.
A modified nystatin technique allowed the investigation of the initial rate of Na+ efflux as a function of internal Na+ content under steady-state conditions in rat thymocytes. This kinetic study showed that 1) ouabain-sensitive Na+ efflux as a function of internal Na+ can be adjusted by a three-sites kinetic model, with a maximal pump rate of 581 +/- 79 mmol.l cells-1.h-1 and an apparent dissociation constant for internal Na+ of 10.0 +/- 1.0 mmol/l cells (mean +/- SE of 3 experiments), 2) bumetanide-sensitive Na+ efflux was extremely low compared with the pump efflux (approximately 1%), and 3) ouabain- and bumetanide-resistant Na+ efflux was almost a linear function of internal Na+ content (as expected for a Na+ leak). This "all-pump" mechanism of thymocyte Na+ regulation was confirmed by non-steady-state experiments showing that 1) ouabain induced a rapid net Na+ gain and K+ depletion in fresh thymocytes and completely blocked the recovery of normal cation contents in Na+-loaded-K+-depleted thymocytes, and 2) bumetanide was unable to modify thymocyte Na+ and K+ contents. Na+ extrusion by Na+-loaded thymocytes was unaffected by prostaglandin E2, isoproterenol, or platelet-aggregating factor (PAF) and was slightly impaired in the adult spontaneously hypertensive rat of the Okamoto strain (10% lower rate constant for net Na+ extrusion, P less than 0.05). Concerning cell Na+ regulation, our results do not support the concept that rat thymocytes are more representative of vascular cells than enucleated erythrocytes.
Senn
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Institut National de la Santé et de la Recherche Médicale U7/CNRS UA 318, Hôpital Necker, Paris, France.
Garay
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RP
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001779:Blood Coagulation Factors / Q000494:pharmacology; D002034:Bumetanide / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D006973:Hypertension / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D010972:Platelet Activating Factor; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
D001779:Blood Coagulation Factors; D010972:Platelet Activating Factor; D015222:Sodium Channels; D002034:Bumetanide; D010042:Ouabain; D012964:Sodium; D015232:Dinoprostone; D007545:Isoproterenol; D011188:Potassium