Chronic effects of type 2 diabetes mellitus on cardiac muscle contraction in the Goto-Kakizaki rat

Experimental Physiology (2007)DOI: 10.1113/expphysiol.2007.038703
Frank Christopher Howarth 1*, Mohamed Shafiullah 1, Mohamed Anwar Qureshi 11 United Arab Emirates University* To whom correspondence should be addressed. E-mail: chris.howarth@uaeu.ac.ae

Type 2 diabetes mellitus (DM) accounts for more than 90 % of all cases of DM and cardiovascular complications are the major cause of mortality and death in diabetic patients. The chronic effects of type 2 DM on heart function have been investigated in the Goto-Kakizaki (GK) rat. Experiments were performed in GK rats and age-matched Wistar controls at 18 months of age. The progressive effects of diabetes on glucose metabolism were monitored periodically by application of the glucose tolerance test. Ventricular action potentials were measured in isolated perfused heart, shortening and intracellular Ca2+ were measured in electrically stimulated ventricular myocytes. GK rats displayed mild fasting hyperglycaemia and progressively worsening glucose tolerance. At 18 months of age and 180 min after intraperitoneal injection of glucose challenge (2 g / Kg body weight) blood glucose was 436 ± 47 mg/dl in GK rats compared to 153 ± 18 mg/dl in controls. Heart weight : body weight ratio was significantly increased in GK rats (4.10 ± 0.09, n=5) compared to controls (3.36 ± 0.22, n=4). Spontaneous heart rate was slightly reduced in GK rats compared to controls. Although the amplitude of shortening was not altered the amplitude of the Ca2+ transient was significantly increased in myocytes from GK (0.78 ± 0.11 RU) rats compared to controls (0.50 ± 0.06 RU). Despite progressively worsening glucose metabolism, at 18 months of age, the contractile function of the heart appears to be well preserved.
(N.B/Reference of the picture: Essentials of Human Physiology by Thomas M. Nosek, Ph.D)