The effect of hypothermia on the Ca2+-pump in sarcoplasmatic reticulum during autolysis of the myocardium

Certain hypothermia action mechanisms on Ca2(+)-pump of the sarcoplasmic reticulum in rat myocardium autolysis are investigated. The complex dependence of Ca2(+)-transporting system preservation in autolysis on the depth of hypothermia is shown. The role of lipid peroxidation and endoproteolysis in a decrease of the autolysing myocardium Ca2(+)-pump activity is considered. A conclusion is drawn that hypothermia does not affect the accumulation of peroxidation products in sarcoplasmic reticulum membranes during myocardium autolysis. The protective action of deep hypothermia on the autolysing myocardium Ca2(+)-pump is realized, at least partially, due to an increase in the Ca2(+)-ATPase active molecules number.     

Induction of diamine oxidase activity in rat kidney during compensatory hypertrophy

Diamine oxidase (EC 1.4.3.6) activity, measured as [¹⁴C]Δ¹-pyrroline formation from [¹⁴C] putrescine, was studied in homogenates of rat kidney during compensatory hypertrophy after unilateral nephrectomy. Acetaldehyde and to a lesser degree phenobarbital, at concentrations which did not modify the activity of a preparation of hog kidney diamine oxidase, increased Δ¹-pyrroline formation in kidney homogenate, which suggests that aldehyde-metabolizing enzymes present in this tissue may interfere with yield of Δ¹-pyrroline and that the use of acetaldehyde may give better information on kidney diamine oxidase activity. Other inhibitors of aldehyde-metabolizing enzymes such as chloral hydrate, disulfiram, and pyrazole cannot be used for diamine oxidase determination since they stimulated or depressed this enzyme activity. In rat kidney undergoing compensatory hypertrophy the levels of putrescine, spermidine, and spermine increased rapidly and were followed by an increase in diamine oxidase activity that presented a first peak on day 2 and a second peak on day 6. The administration of cycloheximide or actinomycin D to nephrectomized rats prevented the increase in diamine oxidase activity. The study of the turnover rate of diamine oxidase with cycloheximide demonstrated that the half-life of this enzyme was about 14 h in normal and hypertrophic kidney. These results suggest that the increase in diamine oxidase activity in renal hypertrophy was due to the synthesis of new enzyme rather than to a slowing of its degradation.     

Time-resolved charge movements in the sarcoplasmatic reticulum Ca-ATPase

The time-resolved kinetics of the Ca(2+)-translocating partial reaction of the sarcoplasmatic reticulum Ca-ATPase was investigated by ATP-concentration jump experiments. ATP was released by an ultraviolet light flash from its inactive precursor and charge movements in the membrane domain of the ion pumps were detected by the fluorescent styryl dye 2BITC. Two oppositely directed cation movements were found, which were assigned to Ca(2+) release and H(+) binding. The faster process with a typical time constant of 30 ms reports the rate-limiting process before Ca(2+) release, probably the conformation transition E(1) --> E(2). The following, slow uptake of positive charge had a pH-dependent time constant, which was 1 s at low pH and approximately 3 s at pH > 8. This process is assigned to an electrically silent conformational relaxation of the state P-E(2) preceding H(+) binding. This interpretation is in agreement with the observation that the fast process was independent of the substrate concentrations (i.e., when [Ca(2+)] > 200 nM, and [ATP] > 20 micro M). The slow process was independent of the Ca(2+) concentration. The activation energy of the resolved processes was between 80 kJ/mol and 90 kJ/mol, which is comparable to the activation energy of the enzymatic activity (92 kJ/mol) and these high values point to conformational changes underlying rate-limiting steps of the pump cycle.     

Electrogenic activity of Ca2+-ATPase fragments of the sarcoplasmatic reticulum during the early stages of radiation injury

It is established that local X-ray irradiation of the rabbit hind limb produces a decrease in Ca2+, Mg2+-ATP-dependent formation of electric potentials difference on the membrane of the sarcoplasmic reticulum (SR). These results agree with the observed decrease in the Ca2+-ATPase activity of SR membranes and increase in their electric conduction after irradiation.     

EMG activity in "compensatory" muscle hypertrophy

The functional elimination of synergistic muscles leads to dramatic muscle hypertrophy. However, neither resting EMG activity recorded by an implanted electrode array, nor activity during locomotion have substantiated the assumption that the hypertrophy in the rat soleus muscle is caused by hyperactivity.     

Enzyme activity of cryoprotected myocardium.

The use of in vivo intravenously infused DMSO/glycerol in Krebs-Henseleit buffer solution as a cryoprotectant in rat left ventricles was investigated. Alkaline phosphatase and creatine phosphokinase activities were monitored. Data show inhibition of alkaline phosphatase by the cryoprotectant solution. No significant differences were noted for the CPK activity indicating that it may not be affected by either freezing or the cryoprotectant or both in combination.     

Effect of actoprotectors on Ca, Mg-dependent ATPase activity in the sarcoplasmatic reticulum of rabbit muscles

The effect of different chemical compounds on Ca, Mg-dependent ATPase (Ca-ATPase) sarcoplasmic reticulum (SR) hydrolytic activity as well as their actoprotecting (AP) activity, the ability to increase organism's resistance under muscle stress and antihypoxanthic (AH) activity to increase the organism's survival under conditions of low pressure has been studied. The compounds with AP-activity have been shown to be strong inhibitors of Ca-ATPase SR hydrolytic activity. No correlation between AP-activity of the compounds and their effect on Ca-ATPase SR has been found. The membranotropic activity of actoprotectors has been shown by electronic paramagnetic resonance method. A suggestion has been made to use Ca-ATPase SR as a tested object during the forecasting actoprotecting activity of new chemical compounds.     

Concentration and adenosinetriphosphatase activity on left ventricular actomyosin in Goldblatt rats during the compensatory stage of hypertrophy.

Left ventricular myocardia of Goldblatt rats with an average increase in arterial blood pressure to about 200 mm Hg showed a progressive reduction of the Ca-activated specific acotmyosin ATPase activity 4 -12 weeks after the coarctation of one renal artery, as compared with controls of the same age. During the same period, a significant increase in the concentration of contractile proteins was noticeable, whereas the content of nonprotein substances and of water corresponded to the control values. The hydroxyproline concentration, as a measure of the collagen tissue content, increased only after 24 weeks. The time course of the specific ATPase activity was closely parallel to the decrease in the unloaded myocardial shortening velocity, as estimated at the same stage by our group. This is in accordance with the assumption of a fundamental relationship between the two values. The reduced rate of energy turnover and of the shortening velocity is regarded as an adaptive mechanism which, however, has a negative effect in advanced hypertrophy when further diminution takes place. The decrease in the specific enzymatic activity of actomysin is not necessarily linked to a large increase in myocardial mass, but is already apparent at moderate degrees of hypertrophy (34%).     

Ribonucleic acid labelling and nucleotide pools during compensatory renal hypertrophy

During the first 48h of compensatory renal hypertrophy induced by unilateral nephrectomy, RNA content per cell increased by 20-40%. During this period, rates of RNA synthesis derived from the rates of labelling of UTP and RNA after a single injection of [5-(3)H]uridine showed no change in the rate of RNA synthesis (3.1nmol of UTP incorporated into RNA/min per mg of RNA). ATP and ADP pools were not changed. The rate of RNA synthesis was considerably in excess of the increment of total RNA appearing in the kidneys. With [5-(3)H]uridine as label, only continuous infusion for 24h could produce an increase (60%) in the specific radioactivity of renal rRNA in mice with contralateral nephrectomies. With a single injection of [methyl-(3)H]methionine used to identify methyl groups inserted into newly synthesized rRNA, the specific radioactivity of this rRNA was unchanged 5h after contralateral nephrectomy, increased by 60% at 9-48h, and returned to normal values at 120h. Most RNA synthesized in both nephrectomized and sham-nephrectomized mice has a short half-life. Since total cellular RNA content increases in compensatory hypertrophy despite unchanged rates of rRNA synthesis, the accretion of RNA might involve conservation of ribosomal precursor RNA or a change in rate of degradation of mature rRNA.