Diabetic rat glomerular mesangial cells display normal inositol trisphosphate and calcium release
Hurst, R.D.; Whiteside, C.I.; Thompson, J.C.
American Journal of Physiology 263(4 Pt 2): F649-F655
1992
ISSN/ISBN: 0002-9513 PMID: 1415736 Document Number: 404466
Since diabetes may cause cellular myo-inositol depletion, we investigated whether the observed in vitro hypocontractile response of streptozotocin (STZ)-treated rat glomeruli to angiotensin II (ANG II) is associated with an alteration in inositol trisphosphate (IP-3) mobilization of intracellular Ca-2+. Contraction of diabetic isolated glomeruli induced by ANG II (5 mu-M), measured in vitro by changes in the planar area, was reduced by 60%, compared with normal up to 60 min (P lt 0.05). In cells of isolated glomeruli, preloaded with myo-(3H)inositol, production of (3H)inositol phosphates ((3H)IPs) and (3H)inositol trisphosphate ((3H)IP-3) was analyzed by Dowex chromatography. ANG II (1 mu-M) evoked an immediate peak (5-10 s) in total (3H)IPs of 60.5 +- 18.8% (mean +- SE) above basal (nonstimulated state) in normal glomeruli, and 88.4 +- 19.4% in diabetic condition (not significant (NS), n = 8). At 60 s, the normal and diabetic total (3H)IPs responses were not significantly different from each other. The immediate (10 s) (3H)IP-3 response from normal glomeruli, 8.1 +- 7.9% above basal, was not significantly different from that of diabetic glomeruli, 15.7 +- 7.4%. ANG II receptor-mediated rise in cytosolic Ca-2+ in the cells of normal and diabetic isolated glomeruli was compared by measuring the efflux of 45Ca-2+. Isolated glomeruli were preloaded with 45Ca-2+. Following ANG II stimulation, peak 45Ca-2+ efflux values at 1 min were 141.7 +- 15.9% (normal) vs. 143.7 +- 7.8% (diabetic) of baseline (100%), respectively (NS, n = 4). Thapsigargin, 2 mu-M, specifically prevented ANG II-stimulated and IP-3-mediated 45Ca-2+ efflux (73% inhibition, P lt 0.001) from cells of whole glomeruli. Cultured rat mesangial cell IP-3-mediated Ca-2+ signaling, measured by indo-1 acetoxymethyl ester fluorescence, following either ANG II or vasopressin, was no different after 5-day exposure to extracellular glucose of 5.56 compared with 25.56 mM. The data imply that diabetic glomerular (mesangial cell) hypocontractility to ANG II is due neither to altered IP-3 signaling nor to intracellular Ca-2+ release.