Changes in cardiac contractility in IDDM and NIDDM diabetic rats.

Differences in myocardial contractility were studied in type I (insulin-dependent, IDDM) and type II (non-insulin-dependent, NIDDM) diabetic rats. Using the streptozotocin-induced diabetes as an experimental model, the contractile properties of left ventricular myocardium of IDDM and NIDDM animals were compared to similar parameters of their age-matched controls. Contraction force was analyzed as a function of the pacing frequency.

Effects of skeletal muscle myosin light chain phosphorylation on synthetic actomyosin ATPase activity and superprecipitation.

In the present study the effect of phosphorylation of skeletal muscle myosin light chains on the interaction between myosin and actin has been investigated. The actomyosin ATPase activities were determined for synthetic actomyosins formed from either phosphorylated or non-phosphorylated myosin and pure actin, with the help of the luciferin-luciferase system. The contractile properties of our preparations were simultaneously studied by the superprecipitation model.

Contractile properties of chick embryo muscles in development.

In this paper we report on the observation of two parameters of embryonic muscles which show the functional activity of myofibrillar ATPase activity of embryonic muscles and superprecipitation (SP) of natural actomyosin. Our results indicate that, during the embryonic period, the myofibrillar ATPase activity and the SP of actomyosin significantly increased, the rate of this increase being different for leg and breast muscles.

[ATPase activity and the contractile capacity of the muscle tissue in chick embryos during development].

The value of ATPase activity of the myofibril preparations and the value and duration of actomyosin superprecipitation were estimated for different muscles during the chick embryonic development. The ATPase level increases during embryogenesis 4.5-fold, in the leg muscle this change takes place distinctly earlier than in the leg muscle.

Effect of immobilization on some glycolytic enzymes of skeletal muscle.

The effect of immobilization by plaster cast was studied on the activities of phosphoglucomutase (PGM), pyruvate kinase ( PyK ) and cAMP-dependent protein kinase in fast (extensor digitorum longus [EDL]), and slow (soleus) muscles of rats. In control untreated animals, PGM and PyK activities are 3 and 5 fold higher respectively in EDL than in soleus in correlation with the high glycolytic activity of fast muscles. During the four weeks period of immobilization a 20% decrease occurred in PGM activity, to which no limiting role in glycolysis is attributed, while PyK which has a regulatory function, showed a 35% decrease in EDL; at the same time in the soleus the activity of these enzymes did not change.

Effect of immobilization on the enzymes of glycogen metabolism.

Activity of the enzymes regulating glycogen metabolism was determined for glycogen phosphorylase (Ph), phosphorylase kinase (PhK) and glycogen synthetase (GS) in fast extensor digitorum longus (EDL) and slow (soleus) muscles of rats following immobilization by plastering. It was shown that the activity not only of Ph but also of PhK was about 8 times higher in the EDL than in the soleus muscle in correlation with the higher glycogenolytic activity of fast muscles. The activity of GS was approximately similar in the two muscles.

Distribution of cholinesterases of rabbit skeletal muscle.

Two cholinesterase (ChE) fractions were extracted from homogenates of rabbit skeletal muscle. One of them the sarcoplasmic ChE could be dissolved quantitatively with solution A. Following the extraction with solution B the myofibrillar ChE fraction could be recovered.