Improvement in cardiac function of diabetic rats by bosentan is not associated with changes in the activation of PKC isoforms.
We previously demonstrated that chronic treatment with the mixed endothelin A and B (ET(A) and ET(B)) receptor blocker bosentan improved isolated working heart function in streptozotocin (STZ) diabetic rats. Endothelin-1 (ET-1) peptide levels, ET-1 mRNA and ET(A) and ET(B) receptor mRNA were all increased in diabetic hearts, but were unaffected by bosentan treatment, indicating that the beneficial effects of bosentan on heart appear to be on downstream effectors of ET-1 and ET receptors rather than the ET-1 system itself. Stimulation of ET-1 receptors leads to increased activation of protein kinase C (PKC), which is associated with PKC translocation from the cytosol to the membrane. Persistent activation of specific PKC isoforms has been proposed to contribute to diabetic cardiomyopathy. The purpose of this study was to determine whether chronic treatment with bosentan influences the activation of PKC isoforms in hearts from diabetic rats. Male Wistar rats were divided into four groups: control, bosentan-treated control, diabetic, and bosentan-treated diabetic. Diabetes was induced by the intravenous injection of 60 mg/kg streptozotocin. One week later, treatment with bosentan (100 mg/kg/day) by oral gavage was begun and continued for 10 weeks. The heart was then removed, homogenized, separated into soluble (cytosolic) and particulate (membrane) fractions and PKC isoform content in each fraction was determined by Western blotting. PKC alpha, beta2, delta, epsilon and zeta were all detected in hearts from both control and diabetic rats. However, no change in the levels or distribution between the soluble and particulate fractions of any of these isoforms could be detected in chronic diabetic hearts compared to control, whether untreated or treated with bosentan. These observations indicate that bosentan does not improve cardiac performance in STZ diabetic rats by affecting the activation of PKC isoforms.
Jiang
Jihong
J
Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, 2146 East Mall, Vancouver, British Columbia V6T 1Z3, Canada.
Yuen
Violet
V
Xiang
Hong
H
McNeill
John H
JH
D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D000077300:Bosentan; D002458:Cell Fractionation; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy* / Q000503:physiopathology; D065128:Endothelin Receptor Antagonists; D004789:Enzyme Activation; D005947:Glucose; D007328:Insulin / Q000097:blood; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017466:Receptors, Endothelin / Q000378:metabolism; D013449:Sulfonamides / Q000627:therapeutic use*; D016277:Ventricular Function, Left / Q000187:drug effects*
D001786:Blood Glucose; D065128:Endothelin Receptor Antagonists; D007328:Insulin; D007527:Isoenzymes; D017466:Receptors, Endothelin; D013449:Sulfonamides; D011493:Protein Kinase C; D005947:Glucose; D000077300:Bosentan