Positive chronotropic actions of parathyroid hormone and parathyroid hormone-related peptide are associated with increases in the current, I(f), and the slope of the pacemaker potential

BACKGROUND: The classic calciotropic hormone parathyroid hormone (PTH) and its paracrine factor parathyroid hormone-related protein (PTHrP) both increase heart rate. METHODS AND RESULTS: We used standard electrophysiological techniques to study the effects of PTH and PTHrP on isolated rabbit sinus node, isolated canine Purkinje fibers, and disaggregated rabbit sinus node myocytes. Sinus node maximum diastolic potential, activation voltage, and amplitude were unchanged by PTH or PTHrP (P>.05). However, the slope of phase 4 and the automatic rate were increased at PTH and PTHrP > or = 10 nmol/L (P<.05). Comparable results were seen in canine Purkinje fibers. We then used the perforated-patch technique to study the I(f) pacemaker current in sinus node. PTH 12.5 nmol/L and PTHrP 12.5 to 18 nmol/L increased I(f) at -65 mV by 68+/-41% (n=5) and 69+/-50% (n=5), respectively. Actions of both agents were reversible. The increase in I(f) appeared to result from a change in maximal conductance and not a shift in the voltage dependence of activation. CONCLUSIONS: These observations provide, for the first time, direct electrophysiological support for the chronotropic actions of PTH and PTHrP. They suggest that classic hormones and paracrine factors can have multiple functions and that in the case of PTH and PTHrP, a newly recognized action is to alter automaticity directly.     

Residual protective effect of <Emphasis Type=Italic>o</Emphasis>-oxyazomethine derivatives against iron corrosion in 1 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution

The residual protective effect of n-component mixtures of o-oxyazomethine derivatives at the corrosion of iron in 1 M H₂SO₄ decreases with time and an increase in temperature of the environment and increases with an increase in the polarity of substituent groups in the molecules and the inhibitor concentration in the solution. These regularities are interpreted based on the principle of the linear free-energy relation.     

Improving the reliability of electric drives of exhausters of the oxygen-converter process

This paper deals with increasing the reliability of electric drives of exhausters of the oxygen-converter process. The dependences of the reliability parameters in the electrical converter–electric motor system on the power reserve were obtained. The costs for the installed equipment were taken as an optimization criterion. It is noted that improving the reliability of an electric drive is possible both by increasing the overall power of the power unit and by changing the number of phases. It is shown that the reliability of the system can be improved in a synchronous electric drive with pulse-vector control at the reservation of a semiconductor converter. A mathematical model of the electrical converter–reluctance motor with a field-regulated machine complex is proposed. The results of the mathematical modeling of the synchronous electric drive with pulse-vector control are considered. The dependence of the specific electric parameters on the number of phases is determined.     

A traction electric drive for electric cars

It is advisable to use a controlled electric drive in electric drives of electric off-road vehicles due to its significant multiplicity of the supported torque (5: 1 and higher) in a low-power mode. Such overloads can be achieved, for example, in electric drives with a field-regulated reluctance machine, not only because of the capacity of the electric machines, but also due to the choice of the drive control system. Analysis of requirements for the electric drive of an electric vehicle is performed, and the influence of the control method on the specific parameters is considered. Analysis of the number of independent control actions in synchronous reluctance electric drives is provided. The possibility of increasing the overload multiplicity of the torque by abandoning the vector control in favor of structures similar to dc drive systems is shown.     

Investigation of 12 – 15 Kev Electron Transmission Through Tapered Glass Capillaries

Glass and Ceramics - The results of experimental studies of the transmission of 12 and 15 keV electron beams through tapered glass macro-capillaries are presented. Measurements showed that there is...     

Correlation of Vibroacoustic Signal with Ceramic Component Wear During Frictional Interaction with a Steel Disc

Refractories and Industrial Ceramics - Complete correlation between dimensions of the wear area on specimens made of oxide-carbide ceramics and the root-mean-square value of vibration acceleration...     

Synthesis and Structure of U(VI), Np(VI), and Pu(VI) 2-Fluorobenzoates

The compounds NH₄[AnO₂(C₆H₄FCOO₃], where An = U (I), Np (II), or Pu (III), CgH₄COO^? is the 2-fluorobenzoate anion, were synthesized and studied by single crystal X-ray diffraction. Compounds I–III are isostructural and crystallize in the cubic system, space group P2₁3, Z = 4. The main structural units of I–III are mononuclear complexes [AnO₂(C₆H₄COO)₃]^? belonging to crystal-chemical group AB₃¹ (A = AnO₂²⁺, B⁰¹ = C₆H₄FCOO^?). The actinide contraction in the structures of I–III is manifested in a regular decrease in the lengths of the An=0 bonds in the AnO₂²⁺ cations and in the volumes of the Voronoi-Dirichlet polyhedra (VDPs) of the An atoms in the series U-Np-Pu. The intermolecular interactions in crystal structures of I–III were analyzed by the method of molecular VDPs.