Motor unit recruitment strategy of knee antagonist muscles in a step-wise, increasing isometric contraction

The purpose of this study was to determine if differences exist between the control strategies of two antagonist thigh muscles during knee flexion and extension muscular coactivation. Surface myoelectric signal (MES) of the quadriceps (rectus femoris) and the hamstrings (semitendinosus) were obtained from both muscles while performing step-wise increasing contractions during flexion and extension with the knee at 1.57 rad of flexion (90 degrees). The median frequency of the power density spectrum, which is related to the average muscle fiber action potential conduction velocity and therefore to motor unit recruitment, was calculated from each MES. The results suggest that, in all the subjects tested, when the muscle acts as antagonist most motor units are recruited up to 50% of the maximal voluntary force, whereas when the muscle acts as antagonist motor units are recruited up to 40% of the maximal voluntary force. The force range past 40–50% of the maximal force is also characterized by differences between the agonist/antagonist.     

Partial purification of a phosphoethanolamine methyltransferase from rat brain cytosol

The conversion of phosphoethanolamine to phosphocholine requires 3 separate N-methyltransferases. We had previously purified the enzyme catalyzing the last methylation, phosphodimethylethanolamine N-methyltransferase. We have successfully purified the enzyme catalyzing the initial methylation of phosphoethanolamine. A 434 fold purified enzyme from rat brain was obtained by the sequential use of ammonium sulfate fractionation, Q-Sepharose fast flow column chromatography and a -aminoethyl agarose column chromatography. The pH optimum was 11 or greater, the Km value for phosphoethanolamine was 167.8±41.7 M and the Vmax was 487.3±85 mmoles/mg/hr. The kinetics for S-adenosyl-methionine, the methyldonor, has characteristics of cooperative binding with a Km of 1.805±0.59 mM and a Vmax of 16.9±3.6 moles/mg/hr. The activity was stimulated 6 fold by 2.5 mM MnCl₂ and inhibited by DZA and S-adenosylhomocysteine. These results reinforce the early in vivo observations which had provided suggestive evidence for the existence of a pathway for the methylation of phosphoethanolamine to phosphocholine in rat brain.Abbreviations used Adomet S-adenosylmethionine - AdoHcy S-adenosyl-homocysteine - CAPS 3-(cyclohexyl)amino-1-propanesulphonic acid - Cho choline - 3-DZA 3-deazaadenosine - Etn ethanolamine - N-MT N-methyltransferase - PEG polyethyleneglycol - PMSF phenylmethanesulphonyl fluoride - PEtn phosphoethanolamine - PCho phosphocholine - PMe₂Etn phosphodimethylethanolamine - PtdCho phosphatidylcholine - PtdEtn phosphatidylethanolamine     

Effects of cytosolic calcium and limited, possible dual, effects of G protein modulators on guard cell inward potassium channels

The cellular mechanisms that regulate potassium (K⁺) channels in guard cells have been the subject of recent research, as K⁺ channel modulation has been suggested to contribute to stomatal movements. Patch clamp studies have been pursued on guard cell protoplasts of Vicia faba to analyze the effects of physiological cytosolic free Ca²⁺ concentrations, Ca²⁺ buffers and GTP-binding protein modulators on inward-rectifying K⁺ channels. Ca²⁺ inhibition of inward-rectifying K⁺ currents depended strongly on the concentration and effectiveness of the Ca²⁺ buffer used, indicating a large Ca²⁺ buffering capacity and pH increases in guard calls. When the cytosolic Ca²⁺ concentration was buffered to micromolar levels using BAPTA, inward-rectifying K⁺ channels were strongly inhibited. However, when EGTA was used as the Ca²⁺ buffer, much less inhibition was observed, even when pipette solutions contained 1 µM free Ca²⁺. Under the imposed conditions, GTPγS did not significantly inhibit inward-rectifying K⁺ channel currents when cytosolic Ca²⁺ was buffered to low levels or when using EGTA as the Ca²⁺ buffer. Furthermore, GDPβS reduced inward K⁺ currents at low cytosolic Ca²⁺, indicating a novel mode of inward K⁺ channel regulation by G-protein modulators, which is opposite in effect to that from previous reports. On the other hand, when Ca²⁺ was effectively elevated in the cytosol to 1 µM using BAPTA, GTPγS produced an additional inhibition of the inward-rectifying K⁺ channel currents in a population of cells, indicating possible Ca²⁺-dependent action of GTP-binding protein modulators in K⁺ channel inhibition. Assays of stomatal opening show that 90% inhibition of inward K⁺ currents does not prohibit, but slows, stomatal opening and reduces stomatal apertures by only 34% after 2 h light exposure. These data suggest that limited K⁺ channel down-regulation alone may not be rate-limiting, and it is proposed that the concerted action of proton-pump inhibition and additional anion channel activation is likely required for inhibition of stomatal opening. Furthermore, G-protein modulators regulate inward K⁺ channels in a more complex and limited, possibly Ca²⁺-dependent, manner than previously proposed.     

Structure-function relationships and molecular genetics of the 3β-hydroxysteroid dehydrogenase gene family

The isoenzymes of the 3β-hydroxysteroid dehydrogenase/5-ene-4-ene-isomerase (3β-HSD) gene family catalyse the transformation of all 5-ene-3β-hydroxysteroids into the corresponding 4-ene-3-keto-steroids and are responsible for the interconversion of 3β-hydroxy- and 3-keto-5-androstane steroids. The two human 3β-HSD genes and the three related pseudogenes are located on the chromosome 1p13.1 region, close to the centromeric marker D1Z5. The 3β-HSD isoenzymes prefer NAD⁺ to NADP⁺ as cofactor with the exception of the rat liver type III and mouse kidney type IV, which both prefer NADPH as cofactor for their specific 3-ketosteroid reductase activity due to the presence of Tyr³⁶ in the rat type III and of Phe³⁶ in mouse type IV enzymes instead of Asp³⁶ found in other 3β-HSD isoenzymes. The rat types I and IV, bovine and guinea pig 3β-HSD proteins possess an intrinsic 17β-HSD activity psecific to 5-androstane 17β-ol steroids, thus suggesting that such “secondary” activity is specifically responsible for controlling the bioavailability of the active androgen DHT. To elucidate the molecular basis of classical form of 3β-HSD deficiency, the structures of the types I and II 3β-HSD genes in 12 male pseudohermaphrodite 3β-HSD deficient patients as well as in four female patients were analyzed. The 14 different point mutations characterized were all detected in the type II 3β-HSD gene, which is the gene predominantly expressed in the adrenals and gonads, while no mutation was detected in the type I 3β-HSD gene predominantly expressed in the placenta and peripheral tissues. The mutant type II 3β-HSD enzymes carrying mutations detected in patients affected by the salt-losing form exhibit no detectable activity in intact transfected cells, at the exception of L108W and P186L proteins, which have some residual activity (1%). Mutations found in nonsalt-loser patients have some residual activity ranging from 1 to 10% compared to the wild-type enzyme. Characterization of mutant proteins provides unique information on the structure-function relationships of the 3β-HSD superfamily.     

Surface proteins in different isolates of Trypanosoma cruzi epimastigotes

Summary Epimastigotes from several Trypanosoma cruzi stocks were labeled by iodination with Chloramine T and their proteins detected by gel electrophoresis and autoradiography.The labeled proteins from the parasite surface were detected after immunoprecipitation with antisera against fixed trypanosomes or from infected rabbits. These antisera were able to recognize one or more proteins in all T. cruzi isolates analyzed, but the individual patterns differed from each other. Variations in the surface protein patterns were also observed in two Tulahuen stocks kept during several years under different conditions. Growth medium as well as the stage of growth at which the parasites were collected had also an effect upon the relative amount of the observed labeled proteins.     

Role of exercise testing early after myocardial infarction in identifying candidates for coronary surgery.

It has been suggested that ST depression in lead V5 or equivalent on early exercise testing after acute myocardial infarction predicts a high risk of death. To evaluate exercise testing and radionuclide ventriculography in this context 103 consecutive patients with myocardial infarction who were able to undertake a limited exercise test before discharge from hospital were exercised and underwent gated blood pool scanning. No serious complications resulted from exercise testing. Twenty nine patients developed ST depression in lead V5, 19 had exertional hypotension, 31 developed a heart rate of greater than or equal to 130 beats/min, and 15 had complex ventricular arrhythmias. Death during the first year after discharge from hospital was associated with exertional hypotension (p less than 0.001) and a heart rate on exercise testing of greater than or equal to 130 beats/min (p less than 0.05); these two variables identified all nine deaths. Inability to complete the exercise protocol for any reason was also predictive of death (p less than 0.01). Ventricular arrhythmias and ST depression in lead V5 induced by exercise were not significantly associated with an increased risk of death. The mean (SD) radionuclide ejection fraction in the patients who died was 29 (16%) compared with 43 (11)% in the patients who survived (p less than 0.001). ST changes on exercise testing after myocardial infarction appear to be less predictive of later complications than haemodynamic signs, which may indicate left ventricular damage rather than ischaemia.     

Structural requirements in the reaction of morphine uridine diphosphate glucuronyltransferase with opioid substances.

The influence of the 3-hydroxyl and N-alkyl groups in the reactivity of narcotic compounds with morphine UDP-glucuronyltransferase was studied. Opioids possessing both, one or none of these groups were tested for inhibition of morphine glucuronidation in rabbit liver microsomal preparations. Compounds with only a 3-hydroxyl group (normorphine) or an N-methyl group (codeine, ethylmorphine) were less potent competitive inhibitors than those containing both groups (dextrorphan). Norcodeine, with neither of these groups, had no inhibitory effect. The synthetic narcotics (+)- and (-)-methadone, (-)-alpha-acetylmethadol and meperidine, with only an N-alkyl group, were effective competitive inhibitors. No stereoselectivity of the morphine glucuronyltransferase for opioid isomers was observed, and [methionine]enkephalin does not react with morphine glucuronyltransferase. Differences of pKa values and water/lipid solubility of narcotics could not explain the effects. Results indicate that the N-alkyl group plays a critical role in the interaction of narcotics with the morphine UDP-glucuronyltransferase.     

Carbohydrate composition of purified serum glycoproteins in Mucolipidosis II and Mucolipidosis III

Summary Mucolipidosis II (I-cell disease) and Mucolipidosis III (ML III) are inherited disorders in which the molecular defect may involve an abnormality in a common post-translational modification step (possibly glycosylation) shared by lysosomal hydrolases. We tested whether such an alteration might be a generalized defect in glycoprotein biosynthesis and, thus, be reflected in an abnormal carbohydrate composition of non-lysosomal glycoproteins. The apoprotein of low density lipoprotein (apo-LDL) and immunoglobulin G (IgG) were purified to apparent homogeneity. Gas liquid chromatographic (glc) analysis of the carbohydrate content of these glycoproteins from ML II, ML III and normal sera revealed no differences in the relative ratios and total amounts of mannose, galactose, N-acetylglucosamine and sialic acid. These results suggest that if the postulated post-translational defect in these disorders involves changes in carbohydrate composition, it is not a general defect in glycosylation and may be specific for lysosomal hydrolases.     

Estimation of the Number of Sex Alleles and Queen Matings from Diploid Male Frequencies in a Population of APIS MELLIFERA

The distribution of diploid males in a population of Apis mellifera was obtained by direct examination of the sexual phenotypes of the larvae. Using these data, estimates are derived for the number of sex alleles and the number of matings undergone by the queen. The number of sex alleles is estimated to be 18.9. The estimate is larger than previous ones, which have ranged between 10 and 12. However, the increase in the number of sex alleles can be explained by the large effective population number for our data. The best estimator of the number of matings by a queen is a maximum likelihood type that assumes a prior distribution on the number of matings. For the data presented here, this estimate is 17.3. This estimate is compared to others in the literature obtained by different approaches.     

The relationship between circulating testosterone levels and male sexual behavior in rats

The relationships between plasma testosterone (T) and various parameters of male sexual behavior were examined in intact and castrated T-treated male rats. Repeated blood sampling and behavioral testing revealed no correlation between any measure of sexual behavior and plasma T in normal untreated sexually active males. T-Filled Silastic capsules, implanted subcutaneously at the time of castration, were found to produce plasma T levels proportional to capsule size. Plasma T titers less than 10% of normal (0.2 ng/ml) maintained ejaculatory behavior near normal levels for the 58 days of the experiment. Measures of sexual behavior which showed androgen dependence were intromission latency, postejaculatory interval, and intromission frequency. The plasma T concentration required to maintain these parameters within the intact range was 0.7 ng/ml, which is less than one-third of the mean intact level (2.6 ng/ml). No significant improvement in the sex behavior measures was seen with plasma T levels between 0.7 and 3.1 ng/ml. It was concluded that the absence of relationships between circulating T and sexual behavior in the normal rat population is due to the androgen requirement for this behavior being less than the amount normally present. Findings on T levels and T treatment in noncopulator males are also presented.