The myofibrillar ATPase activity and the substructure of myosin in the hypertrophied left ventricle of the rat

Summary

The aim of the present study was to seek a possible correlation between changes in enzymatic activity of myofibrils, on the one hand, and the substructure of myosin in hypertrophied myocardium, on the other hand. The myofibrillar ATPase activity and relative quantity of single myosin subunits were investigated in the hypertrophied left ventricle of 10 old male rats with spontaneous hypertension (SHR) and 12 Goldblatt rats (6 months after coarctation of one renal artery) (GBR).

In SHR and GBR the weight of the left ventricle was 47% and 58% greater in comparison with control rats of the same age (WCR and CR respectively). The concentration of myofibrillar proteins was increased by 33% and 22% in SHR and GBR respectively. The myofibrillar ATPase activity ((nmol P_i × mg⁻¹ × min⁻¹) was decreased by 50% in SHR and 30% in GBR. The results of investigation of the relative amount of left ventricular myosin subunits show that the decrease in myofibrillar ATPase activity was associated with a slight decrease in the relative amount of myosin heavy chains (HC) over the amount of light chains 1 and 2 (LC₍₁₊₂₎) in the left ventricle of SHR (16%) and GBR (14%) as compared to control values. The relative amount of myosin light chain 1 to light chain 2 (LC₁ to LC₂) was decreased by 23% and 6% respectively.

On the basis of these results the control mechanism of the synthesis of individual myosin components cannot be ruled out as the regulatory mechanism of specific ATPase activity of contractile proteins of the left ventricle of the rat. A final positive answer to the question of a causal correlation between the structural and enzymatic alteration of myosin will require further biochemical investigation, however.

Supported by the Deutsche Forschungsgemeinschaft.