The making of diabetic guinea pigs by streptozotocin and high incidence of triggered activity in the ventricular muscle.
Myoplasmic Ca2+ metabolism is reported to be impaired in diabetic rat heart. We studied the possibility that the ventricular muscles of diabetic guinea pig are prone to develop delayed afterdepolarizations (DADs) and triggered activity (TA), because DADs and TA are believed to be a possible index of increased level of intracellular Ca2+ concentration. To establish an experimental diabetic model from the guinea pig, male animals were divided into four groups: 1) control group: intracardiac injection of citrate buffer; 2) IP group: intraperitoneal injection of streptozotocin (STZ, 200 mg/kg); 3) IC group: intracardiac injection of STZ; and 4) Ins-IC group: intracardiac injection of STZ after pretreatment with insulin (20 IU/kg). We found that: 1) only in the Ins-IC group was the fasting plasma glucose concentration (determined 40 days after STZ injection) significantly higher than in the control group; 2) oral glucose tolerance test performed 40 days after treatment also showed glucose intolerance in the Ins-IC group. These findings evinced the successful making of diabetic guinea pigs by an intracardiac one-shot injection of STZ during development of insulin-induced hypoglycemia. In vitro electrophysiological experiments were performed on ventricular papillary muscle from diabetic animals (Ins-IC group) by conventional glass microelectrode techniques. Transmembrane action potentials were elicited by pulse trains with various rates (2-5 Hz) and durations (10-30 stimuli) in the presence of ouabain (1 microM) and various Ca2+ concentrations (1.8-7.2 mM). The incidence of TA in the muscles from diabetic animals was significantly higher (chi 2-test, p less than 0.05) than that from controls. The findings gave evidence that Ca2+ homeostasis in the myocardium of diabetic guinea pigs is impaired, and this may be a cause of arrhythmia.
Aomine
M
M
Department of Physiology, Medical College of Oita, Japan.
Nobe
S
S
Arita
M
M
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D004594:Electrophysiology; D006168:Guinea Pigs; D006321:Heart / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D008297:Male; D009206:Myocardium / Q000378:metabolism
D001786:Blood Glucose; D002118:Calcium