Upregulation of D-myo-inositol transport in diabetic rat glomerular cells.
In the streptozotocin (STZ)-treated diabetic rat, reduced glomerular arteriolar resistance leads to raised intraglomerular pressure. Because vasoconstrictor hormones, such as angiotensin II, stimulate arteriolar smooth muscle and mesangial cell contraction via the D-myo-inositol (MI)-dependent transmembrane signaling pathway, in diabetes extracellular D-glucose may inhibit MI transport causing MI depletion, reduced signaling, and hypocontractility. Therefore we studied the regulation of Na-dependent MI transport in the intact cells (mesangial and endothelial) of isolated glomeruli from STZ rats after 2 wk of diabetes, with and without insulin, compared with controls. Specific [3H]MI uptake per milligram glomerular protein (10-150 min, 37 degrees C) was observed in the presence of 0, 5.5, and 30 mM D-glucose using L-[14C]glucose as a marker of nonspecific uptake. D-Glucose competitively inhibited Na-dependent MI transport (maximum velocity) into diabetic and normal glomerular cells. At 5.5 mM D-glucose, MI uptake by diabetic non-insulin-treated glomeruli was increased to 191 +/- 14% (SE) above normal glomeruli. Insulin treatment resulted in less upregulation (116 +/- 11%) of normal MI transport. High glucose concentration did not alter the rate of [3H]MI efflux from preloaded glomerular cells. To determine whether diabetes alters available substrate for transmembrane signaling, after incubation for 120 min, the incorporation of [3H]MI into cellular membrane phosphoinositides and soluble D-myo-inositol phosphates of isolated diabetic and control glomerular cells was compared. Diabetic glomerular cells displayed a significant increase (P less than 0.005) in [3H]MI incorporation into these fractions compared with controls.
Whiteside
C I
CI
Department of Medicine, University of Toronto, Ontario, Canada.
Thompson
J C
JC
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009929:Organ Size / Q000187:drug effects; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D014316:Tritium
D007295:Inositol Phosphates; D007328:Insulin; D010716:Phosphatidylinositols; D014316:Tritium; D007294:Inositol; D005947:Glucose