Autophosphorylation of untrained and well-trained skeletal muscle myosin

Earlier the autophosphorylation of myosin and the labile phosphate (P) content of rabbit skeletal muscle was reported [6, 7, 9]. The present paper describes that the endogeneous preformed P level in fresh preparation of exercised muscle is higher than that of untrained control one. It was revealed that the presence of a significant amount of mitochondrial myosin (with much higher P content) in the well-trained human muscle preparations falsified the appreciation of myofibrillar myosin. Therefore, a reliable myofibrillar preparation with correct P content from exercised subjects was obtained only after the separation of mitochondrial fraction. The P content of fresh preparations can be increased by phosphorylation even in the exercised muscle myosins up to the most higher level in human samples. The phosphoryl group incorporation from [gamma-32P]ATP into the rabbit and hare myosins was checked by radioactive tracer technique, and confirmed by total P content determination performed parallel with molybdate test. It was stated that under present circumstances the labelled 32P incorporation was lower even at an optimal substrate concentration than that of P value obtained directly with molybdate method; because the total P content of preparations had not exchanged during 2 min incubation. So it has been concluded from [gamma-23P] phosphoryl group assayments that much higher amount of P was incorporated into P-Arg, N pi-P-His and fraction 2 as compared with unappreciated labelled P level of the inorganic P (P-Ser, P-Thr), P-Lys, N tau-P-His and minor fractions. From these observations it has been considered that the P-Arg, N pi-P-His and fraction 2 take part in the contraction mechanism and in the course of physical training.     

Electrophysiological changes induced by lysophosphatidylcholine, an ischaemic phospholipid catabolite, in rabbit atrial and ventricular cardiac cells.

The effects of palmitoyl-lysophosphatidylcholine (LPC) were studied on the cellular electrical activity of rabbit heart preparations. LPC (100 mumol/l) caused a considerable enhancement of the automaticity of the SA nodal and Purkinje fibers and frequently induced irregular firing in both supraventricular (SA node, atrium, AV junction) and ventricular (Purkinje fibers, papillary muscle) myocardial regions. The 'automatotropic' and arrhythmogenic effects of LPC were accompanied by a lengthening of the atrioventricular conduction time. In ventricular muscle fibers LPC (100 mumol/l) decreased the resting potential (RP), the maximum rate of depolarization (Vmax) and the amplitude (APA) and duration (APD) of the action potential, and often evoked action potentials of 'slow response' type. In atrial muscle cells, 100 mumol/l LPC was capable of inducing hyperpolarization, with concomitant increases in RP, Vmax, APA and APD; higher concentrations (300 and 600 mumol/l) of LPC resulted in decreases in RP, Vmax, APA and APD, i.e. phenomena similar to those observed with 100 mumol/l LPC in the ventricular myocardium. The results seem to support the assumption that lysolipids accumulating in the ischaemic myocardium may play a pathogenetic role in the development of both supraventricular and ventricular dysrhythmias accompanying coronary artery occlusion.     

Preparation and P content of non-pregnant and pregnant human uterine myosin

Myosin content and phosphorus (P) concentration of myosin preparations were measured in non-pregnant and pregnant human myometrial tissue specimens. It was found that the amount of myosin gained from 1 g of minced myometrial tissue is 0.5 mg in the early follicular phase of the menstrual cycle, 0.6-0.7 mg in the late luteal phase, and 6-7 mg during pregnancy. Considering the different functional stages of the myosin sources and the performance characteristics of the methods, the estimated myosin content of non-pregnant myometrium is 1.0-1.5 mg, while 10-15 mg in pregnant myometrial tissue. A considerable amount of P is bound to the preparations. It is the smallest in the post-menstrual period and increases towards the end of the cycle. The largest amount of P is gained from fresh pregnant uterine samples. Analysis of the alkaline hydrolysate showed that the phosphate group was bound to amino acids, in the largest amount to arginine, less to histidine and the smallest amount to lysine and serine. As a function of the duration of storage, especially the P-Arg concentration was decreasing. The prolonged hydrolysis time decreases again the concentration of P-Arg with a consecutive increase of No. 1 and 2 P-containing peaks in the chromatographic profile of alkaline hydrolysate.     

Effects of L-carnitine in acute myocardial ischaemia

Data in the literature suggest that exogenous L-carnitine improves the metabolic function of ischaemic heart cells: it enhances the transport of long-chain fatty acids into the mitochondria, stimulates the slowed beta-oxidation, and moderates the accumulation of amphiphilic acyl esters. A study has therefore been made of the cardiac effects of L-carnitine in dog experiments (n = 8). The left anterior descending coronary artery (LAD) was isolated in anaesthetized, thoracotomized animals in situ. After a control occlusion and equilibration period, the LAD was again ligated at the time of L-carnitine infusion (100 mg/kg iv. during 10 min). The agent diminished the maximal conduction delay and the degree of epicardial ST-segment elevation in the ischaemic myocardial region, and the free fatty acid concentration of the arterial blood, but it did not influence the frequency of ventricular extrasystoles. The anti-ischaemic effect of L-carnitine was manifest only during the infusion, and its discontinuation was immediately followed by an enhanced ST-segment elevation. In the dose applied, the substance did not affect the heart rate, systemic mean arterial pressure, left ventricular end-diastolic pressure (LVEDP), or left ventricular contractility (LV dP/dtmax). In the canine myocardial infarction model employed it was observed that the duration of the anti-ischaemic effect of L-carnitine (100 mg/kg iv.) is very short, and it has no significant antiarrhythmic action.     

Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D- loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.      

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。