[Temperature dependence of the heat of activation in a single isometric contraction of the rat diaphragm. The effect of extra- and intracellular temperature]. / Temperaturnaia zavisimost' tepla aktivatsii pri odinochnom izometricheskom sokrashchenii diafragmy krysy. Vliianie vne- i vnutrikletochnoi temperatury.

Using a myothermometric method it was found that at 27 degrees and 37 degrees C the activation heat (Qa) of a single isometric contraction of the Wistar's rats isolated diaphragm averages 0.26 +/- 0.02 mcal/g and 0.60 +/- 0.13 mcal/g, accordingly, and Q10 = 2.3. It has been proved that the value of Qa depends on the gradient of intracellular temperature decrease (delta T, r = 0.89, p less than or equal to 0.01) as Qa = 1.68 delta T + 1.30 under 0.01 less than or equal to delta T less than or equal to 1.0. It was concluded that high significance of Qa for the muscles of warm-blooded points to the damaged energetics of the contraction recovery period and delta T is an intracellular informative signal which always determines the value of Qa via the feedback mechanism.

[Noradrenaline regulation of the energy of heat production and ATP utilization during normal single muscle contraction and in hyperoxia]. / Reguliatsiia noradrenalinom énergetiki teploobrazovaniia i utilizatsii ATF pri odinochnom sokrashchenii myshtsy v norme i pri giperoksii.

The effect of noradrenalin (NA, 0.008 microgram/ml) on the rate of heat release (V) during a single isometric contraction of an isolated diaphragm was investigated in rats kept in air and 99% oxygen for 3 hours. The effect was measured by the electrothermometric method in the presence and in the absence of ATP (0.01 mg/ml) in the incubation solution. Hyperoxia doubled V of muscle contraction. The calorigenic effect of NA was not detected in the norm and was very distinct during hyperoxia so that VNA = 0.14X XVinit + 10.88. ATP addition increased V both in the normal and hyperoxic state. However, the increase of the initial V level was 5.3-fold in the hyporexoc state and 1.5-fold in the norm. It is concluded that hyperoxia disturbs energy metabolism of muscle contraction through NA-dependent acceleration of ATP-lytic processes and increase of energy expenditures of heat formation in the course of muscle contraction.

[Changes in the energetics of muscle contraction as a result of hyperoxia]. / Izmenenie énergetiki myshechnogo sokrashcheniia v rezul'tate giperoksii.

Using a highly sensitive thermometric method (1 X 10(-5) degrees C/mm), it was found that the heat production of a single isometric contraction of an isolated diaphragm of the rats exposed to 99% O2 at normal pressure for 3 and 6 hrs significantly differed from the norm: after 3 hr hyperoxygenation muscle heat production increased almost three-fold, and after 6 hr hyperoxygenation it decreased almost two-fold. The increase is regarded as a result of oxygen-potentiated increase of energy expenditures involved in a contraction and of a decrease of the performance of muscle contraction. The decrease is considered as a consequence of the primary in economical energy expenditures by an intensively working muscle represented by the diaphragm and of a reduced viability of the muscle preparation incubated in vitro.

[Changes in the efficiency coefficient of the heart and diaphragm during cold adaptation]. / Izmenenie koéffitsienta poleznogo deistviia serdtsa i diafragmy pri adaptatsii k kholodu.

The heart and diaphragm efficiency seems to be an actively regulated variable. It alters in prolonged adaptation (raises in adaptation to hypoxia; diminishes in cold adaptation which means an increase in heat production per unit of muscle's contractile activity). Enhancement of noradrenaline calorigenic effect on skeletal muscles during cold adaptation is corroborated in an isolated diaphragm. Diminishing of the heart and diaphragm efficiency in thyrotoxicosis suggests participation of thyroid hormones in formation of adaptive decrease of muscular contraction efficiency in cold adaptation. The heart efficiency raises in hypothermia and, probably, in limitation of the myocardium oxygen supply. Possible mechanisms of changes of muscular contraction efficiency are discussed.

[Increase in heat production by muscle contraction caused by 2,4-dinitrophenol]. / Povyshenie teploproduktsii myshechnogo sokrashcheniia pod deistviem 2,4-dinitrofenola.

By means of a highly sensitive thermometric method (1.10--50 C/mm) it was possible to demonstrate that the heat production during a single contraction of the isolated rat diaphragm increased under the influence of 2,4-dinitrophenol (DNP). Low DNP concentrations failed to produce any manifest changes in the resting muscle, but its action was distinct during contraction. With the same muscle contraction force DNP action was followed by an increase (about 1 1/2-fold) of heat production. This fact confirmed a supposition on the leading role of oxidation and phosphorylation uncoupling in the muscle cell respiratory chain in the increase of muscle contraction heat production in the animals after cold adaptation.

[Effect of thyroxine and noradrenaline on the energetics of muscle contraction]. / Vliianie tiroksina i noradrenalina na énergetiku myshechnogo sokrashcheniia.

The highly sensitive thermometric method (1.10(-5) degrees C/mm) revealed that the heat production of single contraction of the isolated rat diaphragmal muscle with artificial hyperthyrosis (HD) is nearly double of that of the normal muscle (ND). Noradrenaline added to the inculation solution entailed a greater increase of heat production of the muscle contraction in HD and had no significant effect on ND. However, calorific effect of thyroid hormone was about twice and a half as great as that of noradrenaline. These data suggest that thyroxin acts independently in the energy regulation during the cold acclimation of the organism, and the calorific effects of both hormones can be more effectively realized just at the moment of muscle contraction.