ATP-Dependent Calcium Uptake in Myocardial Sarcoplasmic Reticulum from Spontaneously Hypertensive Rats: Effect of Modification of Dietary Protein

Abstract

Membrane fractions enriched in sarcoplasmic reticulum (SR) were isolated from the cardiac ventricles of 10-month-old, stroke-prone spontaneously hypertensive rats (SHRSP) which had been maintained for nine months on one of four experimental diets: low protein (LP) (19% protein), standard (STD) (24% protein), high protein (HP) (32% protein), or high methionine (1.9% methionine) (MET). ATPase activities, as well as ATP-dependent Ca²⁺ binding and Ca²⁺ uptake activities, of the isolated SR were determined to examine the influence of diet on myocardial Ca²⁺ -pump activity. SR from all four groups exhibited similar Mg²⁺ ATPase activity. However, the (Ca²⁺ Mg²⁺)-ATPase activity was significantly elevated in SR from rats on the MET diet while the activity in the other groups showed no significant differences. After 15 sec of incubation. Ca²⁺ -uptake (presence of oxalate) in SR from the LP group was significantly less than Ca²⁺ -uptake in SR from each of the three other diet groups. Ca²⁺ binding (absence of oxalate) in the SR from the LP group was also significantly less than that from each of the three other diet groups. Kinetic analysis of SR Ca²⁺ -uptake over 60 sec revealed that the B_max of the MET group was significantly higher than B_max of the STD diet group. In addition, the B_max of the LP group was significantly lower than B_max of the HP and MET groups. There was no significant difference in affinity of the SR Ca²⁺ -uptake system among the four diet groups. These results indicate that modification of dietary protein can influence myocardial SR Ca²⁺ -pump function.

Key Words:

• Spontaneously hypertensive rats (SHR)
• Ca²⁺ transport
• (Ca²⁺+ Mg²⁺)-ATPase
• diet
• heart