GLYCOSYLATION OF HEART MYOGLOBIN IN DIABETIC RATS

Abstract

We have reported cardiopathy in juvenile diabetics in poor control which improves with good glycemic control (Ped Res 16: 97A, 1982). Glycosylation of heart myoglobin may play a role in this type of reversible diabetic cardiopathy. Myoglobin is similar to the B-chain of hemoglobin (Hgb) and has a sufficient number of lysine residues and amino terminus to be glycosylated like Hgb. Twelve rats, 2m old, were injected with 60mg/kg streptozotocin by the penial vein and 12 control (C) rats were injected with saline. Glycosuria and hyperglycemia (blood sugar greater than 400mg/dl) were present in the diabetic (D) rats. After 12 wks the rats were killed. Hearts were perfused through coronary arteries with 0.85% NaCl until clear. D had heart wts of 1.11±0.07 gm vs C 0.98±0.18 gm. Hearts were minced in a mortar, leached with 10 times its volume 0.01M potassium phosphate buffer, pH 7.0, with 5mM EDTA and centrfigued at 20,000 g for 10 min. The clear supernatant containing myoglobin was filtered through a 1.6 × 40cm column of Sephadex G-100 superfine gel and diluted in 2.1ml fractions with the phosphate buffer. Protein was measured by Lowry and glycosylation by the modified TBA method of Ney et al (Anal. Biochem 118:294, 1981). D rats had 8.26±2.50 (m±SE) OD443 per mg protein and control 2.19±0.32, P<0.005. Markedly increased glycosylation of heart myoglobin may change the oxygen affinity and subsequently the contractibility of cardiac muscle and contribute to the cardiopathy of juvenile diabetics in poor control.

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