Effects of urea on K+ fluxes and cell volume in perfused rat liver.
Exposure of the perfused rat liver to a perfusate made hyperosmotic by the presence of 200 mmol l-1 glucose led, as expected, to marked, transient hepatocellular shrinkage followed by volume-regulatory net K+ uptake. However, even after this volume-regulatory K+ uptake had ceased, the liver cells are still slightly shrunken. Withdrawal of glucose from the perfusate resulted in marked transient cell swelling, net K+ release from the liver and restoration of cell volume. However, when the Krebs-Henseleit perfusate was made hyperosmotic by the presence of urea (20-300 mM), there was no immediate decrease in liver mass, yet a slight and persistent cell shrinkage developing 2 min after the onset of exposure to urea. Surprisingly, urea induced concentration-dependent net K+ efflux from the liver and removal of urea net K+ reuptake from the inflowing perfusate. The urea (200 mM)-induced net K+ release resembled that observed following a lowering of the influent [NaCl]: making the perfusate hypoosmotic (245 mosmol l-1, by reducing influent [NaCl] by 30 mM) gave roughly the same K+ response as hyperosmotic exposure (505 mosmol/l) resulting from the presence of 200 mM urea. The urea-induced K+ efflux was not inhibited in the presence of ouabain (1 mM), or in Ca(++)-free perfusion, but was modified in the presence of quinidine (1 mM) or Ba++ (1 mM). The direction in which the liver was perfused had no effect on the urea-induced net K+ release.(ABSTRACT TRUNCATED AT 250 WORDS)
Hallbrucker
C
C
Medizinische Universitätsklinik Freiburg, Germany.
vom Dahl
S
S
Ritter
M
M
Lang
F
F
Häussinger
D
D
D000818:Animals; D004553:Electric Conductivity; D005947:Glucose / Q000494:pharmacology / Q000502:physiology; D008099:Liver / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008297:Male; D010477:Perfusion; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014508:Urea / Q000494:pharmacology*
D014508:Urea; D005947:Glucose; D011188:Potassium