Inhibition of hepatic proteolysis by insulin. Role of hormone-induced alterations of the cellular K+ balance.
1. Proteolysis was measured as [3H]leucine release from isolated perfused livers from rats, which had been labeled in vivo by an intraperitoneal injection of [3H]leucine about 16 h prior to the perfusion experiment. In livers from fed rats, insulin (35 nM) inhibited [3H]leucine release by 24.5 +/- 1.3% (n = 15) and led to an amiloride-sensitive, bumetanide-sensitive and furosemide-sensitive net K+ uptake of 5.53 +/- 0.31 mumol.g-1 (n = 15). Both the insulin effects on net K+ uptake and on [3H]leucine release were diminished by about 65% or 55% in presence of furosemide (0.1 mM) or bumetanide (5 microM), respectively. The insulin-induced net K+ uptake was virtually abolished in the presence of amiloride (1 mM) plus furosemide (0.1 mM). 2. In perfused livers from 24-h-starved rats, both the insulin-stimulated net K+ uptake and the insulin-induced inhibition of [3H]leucine release were about 80% lower than observed in experiments with livers from fed rats. The insulin effects on K+ balance and [3H]leucine release were not significantly influenced in the presence of glycine (2 mM), although glycine itself inhibited [3H]leucine release by 30.3 +/- 0.3% (n = 4) and 13.8 +/- 1.2% (n = 5) in livers from starved and fed rats, respectively. When livers from fed rats were preswollen by hypoosmotic perfusion (225 mOsmol.l-1), both the insulin-induced net K+ uptake and the inhibition of [3H]leucine release were diminished by 50-60%. 3. During inhibition of [3H]leucine release by insulin, further addition of glucagon (100 nM) led to a marked net K+ release from the liver (3.82 +/- 0.24 mumol.g-1), which was accompanied by stimulation of [3H]leucine release by 16.4 +/- 4.6% (n = 4). 4. Ba2+ (1 mM) infusion led to a net K+ uptake by the liver of 3.2 +/- 0.2 mumol.g-1 (n = 4) and simultaneously inhibited [3H]leucine release by 12.4 +/- 1.7% (n = 4). 5. There was a close relationship between the Ba2+ or insulin-induced net K+ uptake and the degree of inhibition of [3H]leucine release, even when the K+ response to insulin was modulated by bumetanide, furosemide, glucagon, hypotonic or glycine-induced cell swelling or the nutritional state. 6. The data suggest that the insulin-induced net K+ uptake involves activation of both NaCl/KCl cotransport and Na+/H+ exchange.(ABSTRACT TRUNCATED AT 400 WORDS)
Hallbrucker
C
C
Medizinische Universitätsklinik, Freiburg, Federal Republic of Germany.
vom Dahl
S
S
Lang
F
F
Gerok
W
W
Häussinger
D
D
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D006982:Hypertonic Solutions; D007038:Hypotonic Solutions; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D011480:Protease Inhibitors; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D006982:Hypertonic Solutions; D007038:Hypotonic Solutions; D007328:Insulin; D011480:Protease Inhibitors; D011506:Proteins; D002034:Bumetanide; D000584:Amiloride; D005665:Furosemide; D007930:Leucine; D011188:Potassium; D005998:Glycine