Extracellular glucose reduces the responsiveness of mesangial cell ion channels to angiotensin ii. Seal, Elisabeth E., Douglas C. Eaton, Lourdes M. Gomez, Heping Ma, and Brian N. Ling. Renal Division, Departments of Medicine and Physiology, Emory University School of Medicine and Veterans Affairs Medical Center, Atlanta, Georgia
APStracts 2:0029F, 1995.
Abnormal cellular ion homeostasis is a well recognized component of diabetic glomerular disease (2,3,21). In cultured rat glomerular mesangial cells, we have previously shown that insulin regulates Ca2+-dependent, activation of 4 pS Cl- channels and 27 pS nonselective cation channels (NSCC) by angiotensin II (AII) (22,23). To assess whether extracellular glucose also affects mesangial ion channels, we applied patch clamp techniques to cells incubated in constant insulin (100 mU/ml), and either $QUOTnormal$QUOT (5 mM) or $QUOThigh$QUOT (30 mM) glucose for 1 week. In normal glucose, 100 nM AII increased Cl- and NSCC activity by > 16-fold and > 60-fold, respectively. Direct release of intracellular [Ca2+]i stores (0.25 NM thapsigargin) mimicked AII-induced, channel stimulation. In high glucose, Cl- and NSCC stimulation by AII was attenuated (< 7-fold), while channel activation by thapsigargin was unaffected. Protein kinase C (PKC) inhibition (30 min. exposure to 0.5 NM calphostin) or down-regulation (24 hr. exposure to 0.1 NM PMA), but not aldose reductase inhibition (0.5 mM sorbinil), restored channel responsiveness to AII despite high glucose. Channel responsiveness was also restored if mesangial cells were co-incubated in both high glucose and 500 NM myo-inositol. Acute exposure to a synthetic diacyglycerol (100 NM OAG) reestablished channel unresponsiveness to AII. We conclude that in rat mesangial cell cultures: 1) Activation of Ca2+-dependent, Cl- and NSCC's by AII is reduced by high extracellular glucose. 2) The inhibitory effect of high glucose occurs at a step proximal to AII-mediated, release of intracellular [Ca2+]i stores, and involves myo-inositol depletion and PKC activation. 3) In diabetic patients, hyperglycemia would be predicted to decrease the responsiveness of glomerular mesangial cell ion channels to the vasoactive peptide, AII. 

Received 20 June 1994; accepted in final form 2 March 1995.
APS Manuscript Number F206-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.