Contraction and intracellular free Ca²⁺ concentration in ventricular myocytes from rats receiving sucrose-enriched diets

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.