Group I introns in the liverwort mitochondrial genome: the gene coding for subunit 1 of cytochrome oxidase shares five intron positions with its fungal counterparts.

The complete nucleotide sequence of the mitochondrial DNA (mtDNA) from a liverwort, Marchantia polymorpha, contains thirty-two introns. Twenty-five of these introns possess the characteristic secondary structures and consensus sequences of group II introns. The remaining seven are group I introns, six of which happen to interrupt the gene coding for subunit 1 of cytochrome oxidase (cox1). Interestingly, the insertion sites of one group II and four group I introns in the cox1 gene coincide with those of the respective fungal mitochondrial interns. Moreover, comparison of the four group I introns with their fungal counterparts shows that group I introns inserted at identical genomic sites in different organisms are indeed related to one another, in terms of the peptide sequences generated from the complete or fragmental ORFs encoded by these introns. At the same time, the liverwort introns turned out to be more divergent from their fungal cognates than the latter are from one another. We therefore conclude that vertical transmission from a common ancestor organism is the simplest explanation for the presence of cognate introns in liverwort and fungal mitochondrial genomes.     

[2-3H]ATP synthesis and 3H NMR spectroscopy of enzyme-nucleotide complexes: ADP and ADP.Vi bound to myosin subfragment 1

Summary The synthesis of [2-³H]ATP with specific activity high enough to use for ³H NMR spectroscopy at micromolar concentrations was accomplished by tritiodehalogenation of 2-Br-ATP. ATP with greater than 80% substitution at the 2-position and negligible tritium levels at other positions had a single ³H NMR peak at 8.20 ppm in 1D spectra obtained at 533 MHz. This result enables the application of tritium NMR spectroscopy to ATP utilizing enzymes.The proteolytic fragment of skeletal muscle myosin, called S1, consists of a heavy chain (95 kDa) and one alkali light chain (16 or 21 kDa) complex that retains myosin ATPase activity. In the presence of Mg²⁺, S1 converts [2-³H]ATP to [2-³H]ADP and the complex S1.Mg[2-³H]ADP has ADP bound in the active site. At 0°C, 1D ³H NMR spectra of S1.Mg[2-³H]ADP have two broadened peaks shifted 0.55 and 0.90 ppm upfield from the peak due to free [2-³H]ADP. Spectra with good signal-to-noise for 0.10 mM S1.Mg[2-³H]ADP were obtained in 180 min. The magnitude of the chemical shift caused by binding is consistent with the presence of an aromatic side chain being in the active site. Spectra were the same for S1 with either of the alkali light chains present, suggesting that the alkali light chains do not interact differently with the active site. The two broad peaks appear to be due to the two conformations of S1 that have been observed previously by other techniques. Raising the temperature to 20 °C causes small changes in the chemical shifts, narrows the peak widths from 150 to 80 Hz, and increases the relative area under the more upfield peak. Addition of orthovanadate (V_i) to produce S1.Mg[2-³H]ADP.V_i shifts both peaks slightly more upfield without chaning their widths or relative areas.     

Tissue distribution of antihypertensive dipeptide, Val-Tyr, after its single oral administration to spontaneously hypertensive rats.

The distribution of an antihypertensive dipeptide, Val-Tyr (VY), in the tissues of spontaneously hypertensive rats (SHR) was investigated in this study. A single oral administration of VY (10 mg/kg) to 18-week-old SHR resulted in a prolonged reduction of systolic blood pressure (SBP) up to 9 h (SBP0h 198.0+/-3.6 mmHg; SBP9h 154.6+/-3.5 mmHg). As a result of VY determination, a roughly 10-fold higher increment of plasma VY level was observed at 1 h than that at 0 h, whereas thereafter the level declined rapidly. In tissues, VY was widely accumulated in the kidney, lung, heart, mesenteric artery and abdominal aorta with the area under the curve over 9 h of more than 40 pmol h/g tissue; of these a higher VY level was observed in the kidney and lung. In addition, a mean resident time (MRT) for each tissue (>5 h except for liver) revealed that VY preferably accumulated in the tissues rather than in the plasma (MRT 3.8 h). Significant reductions of tissue angiotensin I-converting enzyme activity and angiotensin II level were found in the abdominal aorta as well as in the kidney, suggesting that these organs could be a target site associated with the antihypertensive action of VY.     

Mechanomyographic and electromyographic responses of the triceps surae during maximal voluntary contractions.

The objective of this study was to examine the effect of joint angle on the electromyogram (EMG) and mechanomyogram (MMG) during maximal voluntary contraction (MVC). Eight subjects performed maximal isometric plantar flexor torque productions at varying knee and/or ankle angles. Maximal voluntary torque, EMG, and MMG from the soleus (Sol), medial (MG) and lateral gastrocnemius (LG) muscles were measured at different joint angles. At varying knee angles, the root mean squared (rms) MMG amplitude of the MG and LG increased with knee joint extension from 60 degrees to 180 degrees (full extension) in steps of 30 degrees, whereas that of the Sol was constant. At varying ankle angles, the rms-MMG of all muscles (Sol, MG, and LG) decreased with torque as ankle joint extending from 80 degrees (10 degrees dorsiflexion position) to 120 degrees (30 degrees plantar flexion position) in steps of 10 degrees. In each case, changes in the rms-MMG of the three muscles were almost parallel to those in torque. In contrast, there were no significant differences in the rms-EMG of all muscles among all joint angles. Our data suggest that the MMG amplitudes recorded from individual muscles during MVCs can represent relative torque-angle relationships that cannot be represented by the EMG signals.     

Mycoplasma orale infection affects K+ and Cl− currents in the HSG salivary gland cell line

Summary The relations between K⁺ channel and Cl⁻ channel currents and mycoplasma infection status were studied longitudinally in HSG cells, a human submandibular gland cell line. The K⁺ channel currents were disrupted by the occurrence of mycoplasma infection: muscarinic activation of K⁺ channels and K⁺ channel expression as estimated by ionomycin- or hypotonically induced K⁺ current responses were all decreased. Similar decreases in ionomycin- and hypotonically induced responses were observed for Cl⁻ channels, but only the latter decrease was statistically significant. Also, Cl⁻ currents could be elicited more frequently than K⁺ currents (63% of cases versus 0%) in infected cells when tested by exposure to hypotonic media, indicating that mycoplasma infection affects K⁺ channels relatively more than Cl⁻ channels. These changes occurred in the originally infected cells, were ameliorated when the infection was cleared with sparfloxacin, and recurred when the cells were reinfected. Such changes would be expected to result in hyposecretion of salivary fluid if they occurredin vivo.     

Force-dependent changes in movement-related cortical potentials

The purpose of this study was to compare movement-related cortical potentials (MRCPs) associated with different levels of isometric contractions by elbow flexors. Eight healthy, right-handed male subjects participated in this study and performed different levels (10 and 50% of maximal voluntary contraction) of isometric contractions by the right elbow flexors. Electroencephalogram (EEG) signals were recorded from Fz, C3, Cz and C4 of the international 10/20 system. Motor potential (MP) amplitudes (from −200 to approximately −50 ms before force onset) for C3 associated with both force generations was significantly greater (P < 0.01) than those for C4, indicating that contralateral predominance of MRCP was observed in the right arm flexion. In Fz, the potentials of negative slope (NS′) (from −600 to approximately −200 ms) and MPs for 50% MVC were significantly greater than those of 10% MVC. In Cz, the MP associated with 50% MVC revealed a significantly greater (P < 0.05) value than that with 10% MVC. In C3 and C4, the MP associated with 50% MVC tended to be greater than that with 10% MVC, but no statistically significant differences were found. These force-dependent changes in MRCPs imply increased activation of neural circuits involved in motor preparation and initiation. It is therefore suggested that the larger potentials from Fz and Cz for 50% MVC compared with 10% MVC reflect a greater activation of supplementary motor area for the preparation of the larger force generation.     

Cryopreservation of wild mouse spermatozoa

Spermatozoa of wild mice from China, Czechoslovakia, Denmark, India, Japan and Switzerland were frozen and stored at -196 degrees C. After thawing, intact oocytes were inseminated in vitro with relatively high motility frozen-thawed mouse spermatozoa from Czechoslovakia, Denmark and India, while oocytes with a partially dissected zona were inseminated with low motility frozen-thawed spermatozoa from China, Japan and Switzerland. Embryos developing to the 2-cell stage from oocytes fertilized with frozen-thawed spermatozoa were transferred to the oviducts of female recipients on the first day of pseudopregnancy (day when a vaginal plug was confirmed). Successful embryo development to the 2-cell stage was 46 to 67%. Offspring resulted from 17 to 51% of these transferred 2-cell embryos.