ISSN No. 1606-7754                   Vol.12 No.1&2  April-August 2004

Contraction and intracellular free Ca2+ concentrations in ventricular myocytes from rats receiving sucrose-enriched diets
F C Howarth, A Qureshi and E Adeghate
Faculty of Medicine & Health Sciences, United Arab Emirates University, Al Ain, UAE

Abstract

Contraction and intracellular free Ca2+ concentrations [Ca2+]i in ventricular myocytes from rats receiving sucrose-enriched diets (SED’s) were investigated. Groups of Wistar rats received normal rat chow together with either normal drinking water or water containing 500 mM sucrose ad libitum. Experiments were performed 12-14 weeks later. Rats receiving SED’s responded differently to a standard glucose tolerance test. Fasting blood glucose levels in SED and control rats were 59.4±1.3 and 58.8±1.4 mg/dl, respectively. At 30 min after intraperitoneal administration of glucose (2g/kg body weight) concentrations of blood glucose were significantly (P<0.05) higher in rats receiving SED (256.2 ±32.7 mg/dl) compared to controls (136.6±14.7 mg/dl). At 120 min blood glucose in SED (67.6±7.2) and control (63.0±2.4 mg/dl) rats were not significantly (P>0.05) different when compared to initial fasting blood glucose values. Blood plasma insulin concentrations in SED and control rats were 3.01±0.55 (5) and 0.29±0.05 (5) ng/ml, respectively. Amplitude and time to peak (TPK) of ventricular myocyte shortening and Ca2+ transient were not altered by SED. Time to half (THALF) relaxation of shortening was significantly prolonged in myocytes from SED (60.6±2.1 ms) compared to control (48.7±2.9 ms) rats. The TPK and THALF relaxation of the Ca2+ transient were not altered by SED. However, the amplitude of Ca2+ transient was significantly increased in myocytes from SED (0.36±0.02 RU) compared to control (0.31±0.02 RU) rats. Altered myofilament sensitivity to Ca2+ may underlie the contractile defects seen in ventricular myocytes from rats fed diets that are supplemented with drinking water containing 500 mM sucrose for 12-14 weeks.

Keywords : Sucrose, ventricular myocytes, contraction, intracellular calcium

Introduction

The hallmarks of type 2 non-insulin dependent diabetes mellitus (NIDDM) are impaired insulin action in peripheral tissues and decreased pancreatic beta-cell function. Genetic and lifestyle factors including consumption of high-calorie diets, lack of exercise and consequent weight gain are all risk factors associated with the etiology of type 2 diabetes. Previous studies have demonstrated that chronic sucrose-feeding in rats leads to a condition which shares some characteristics with type 2 diabetes mellitus including resting hyperglycaemia, high circulating insulin and triglyceride levels.1,2,3 In this study, we have investigated the effects of sucrose-enriched diets (SED’s) on ventricular myocyte contraction and intracellular Ca2+ in rats.

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