Efflux of potassium (86Rb+) attenuates the volume-restorative effect of sodium-amino acid cotransport in rat renal inner medullary cells shrunken by exposure to hyperosmotic media.
When the osmolality of the bathing medium was increased from 710 to 2000 mosmol/kg H2O, cells in incubated slices of rat renal inner medulla lost water and K+, and the rate of efflux of preloaded 86Rb+ (a tracer for K+) was significantly depressed. Addition of 2-aminoisobutyric acid (AIB, 10 mmol/l) partly restored cell water content but without re-accumulation of K+; the rate of 86Rb+ efflux was greatly increased. The presence of Ba2+ (1 mmol/l) or trifluoperazine (50 mumol/l) led to complete recovery of cell volume and K+ contents, with markedly reduced efflux of 86Rb+. Neither additive had any significant effect upon these variables in the absence of AIB or in media of 710 mosmol/kg. Efflux of 86Rb+ was pH-sensitive within the physiological range, and was depressed when external AIB was reduced below approx. 5 mmol/l. When external Na+ was increased from 145 to 500 mmol/l (total osmolality 350 to 2500 mosmol/kg) efflux was retarded only slightly if AIB was present, but markedly if AIB was omitted. Inner medullary cells may contain a class of Ba(2+)-inhibitable, calmodulin-dependent K+ conductive pathway which is activated in strongly hyperosmotic media by the operation of an inwardly-directed Na(+)-amino acid symport (cf. Law, R.O. (1988) Pflügers Arch. 413, 43-50) and which serves to moderate the volume-restorative effect of this membrane mechanism.
Law
R O
RO
Department of Physiology, University of Leicester, UK.
D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009997:Osmotic Pressure; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012414:Rubidium Radioisotopes; D012964:Sodium / Q000378:metabolism*
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D002352:Carrier Proteins; D012414:Rubidium Radioisotopes; C100049:2-aminoisobutyric acid; D012964:Sodium; D011188:Potassium