Dual Activation of Phosphodiesterases 3 and 4 Regulates Basal Spontaneous Beating Rate of Cardiac Pacemaker Cells: Role of Compartmentalization?

Spontaneous firing of sinoatrial (SA) node cells (SANCs) is regulated by cyclic adenosine monophosphate (cAMP)-mediated, protein kinase A (PKA)-dependent (cAMP/PKA) local subsarcolemmal Ca2+ releases (LCRs) from ryanodine receptors (RyR). The LCRs occur during diastolic depolarization (DD) and activate an inward Na+/Ca2+ exchange current that accelerates the DD rate prompting the next action potential (AP). Basal phosphodiesterases (PDEs) activation degrades cAMP, reduces basal cAMP/PKA-dependent phosphorylation, and suppresses normal spontaneous firing of SANCs. The cAMP-degrading PDE1, PDE3, and PDE4 represent major PDE activities in rabbit SANC, and PDE inhibition by 3-isobutyl-1-methylxanthine (IBMX) increases spontaneous firing of SANC by ∼50%. Though inhibition of single PDE1–PDE4 only moderately increases spontaneous SANC firing, dual PDE3 + PDE4 inhibition produces a synergistic effect hastening the spontaneous SANC beating rate by ∼50%. Here, we describe the expression and distribution of different PDE subtypes within rabbit SANCs, several specific targets (L-type Ca2+ channels and phospholamban) regulated by basal concurrent PDE3 + PDE4 activation, and critical importance of RyR Ca2+ releases for PDE-dependent regulation of spontaneous SANC firing. Colocalization of PDE3 and PDE4 beneath sarcolemma or in striated patterns inside SANCs strongly suggests that PDE-dependent regulation of cAMP/PKA signaling might be executed at the local level; this idea, however, requires further verification

Effect of Cavβ Subunits on Structural Organization of Cav1.2 Calcium Channels

BACKGROUND:Voltage-gated Ca(v)1.2 calcium channels play a crucial role in Ca(2+) signaling. The pore-forming alpha(1C) subunit is regulated by accessory Ca(v)beta subunits, cytoplasmic proteins of various size encoded by four different genes (Ca(v)beta(1)-beta(4)) and expressed in a tissue-specific manner. METHODS AND RESULTS:Here we investigated the effect of three major Ca(v)beta types, beta(1b), beta(2d) and beta(3), on the structure of Ca(v)1.2 in the plasma membrane of live cells. Total internal reflection fluorescence microscopy showed that the tendency of Ca(v)1.2 to form clusters depends on the type of the Ca(v)beta subunit present. The highest density of Ca(v)1.2 clusters in the plasma membrane and the smallest cluster size were observed with neuronal/cardiac beta(1b) present. Ca(v)1.2 channels containing beta(3), the predominant Ca(v)beta subunit of vascular smooth muscle cells, were organized in a significantly smaller number of larger clusters. The inter- and intramolecular distances between alpha(1C) and Ca(v)beta in the plasma membrane of live cells were measured by three-color FRET microscopy. The results confirm that the proximity of Ca(v)1.2 channels in the plasma membrane depends on the Ca(v)beta type. The presence of different Ca(v)beta subunits does not result in significant differences in the intramolecular distance between the termini of alpha(1C), but significantly affects the distance between the termini of neighbor alpha(1C) subunits, which varies from 67 A with beta(1b) to 79 A with beta(3). CONCLUSIONS:Thus, our results show that the structural organization of Ca(v)1.2 channels in the plasma membrane depends on the type of Ca(v)beta subunits present

Soluble Thrombomodulin and Major Orthopedic Surgery

Background: A high level of soluble thrombomodulin (sTM) is associated with a lower risk of thrombosis but can cause severe bleeding after operations. Deep vein thrombosis (DVT) and blood loss are serious threats after orthopedic surgery. The aim of our pilot study was to evaluate the effect of the preoperative level of sTM on coagulation and inflammation as well as the blood loss and the development of symptomatic DVT after total large joint replacement. Methods and Results: In all patients (n=50) who underwent total hip or knee replacement, sTM, PrC, D-dimer, vWF, CRP, and platelets were determined before and after the operation. According to the preoperative sTM level, patients were divided into 2 groups: the thrombomodulin low (TML) group (n=25) and thrombomodulin high (TMH) group (n=25). The concentration of sTM was 4.4 [3.4, 4.7] ng/ml in the TML-group and 8.7[7.3, 10.6] ng/ml in the TMH-group. After surgery, D-dimer, vWF, platelet count and CRP were higher and total blood loss was lower in the TML group. In the TML-group, a symptomatic DVT was detected in 3(12%) patients; in the TMH-group, a symptomatic DVT was identified only in 1(4%) case. Conclusion: These findings support the important role of sTM in coagulation, inflammation, bleeding, and presumably in venous thrombosis after major orthopedic surgery

Searching for Better Plasmonic Materials

Plasmonics is a research area merging the fields of optics and nanoelectronics by confining light with relatively large free-space wavelength to the nanometer scale - thereby enabling a family of novel devices. Current plasmonic devices at telecommunication and optical frequencies face significant challenges due to losses encountered in the constituent plasmonic materials. These large losses seriously limit the practicality of these metals for many novel applications. This paper provides an overview of alternative plasmonic materials along with motivation for each material choice and important aspects of fabrication. A comparative study of various materials including metals, metal alloys and heavily doped semiconductors is presented. The performance of each material is evaluated based on quality factors defined for each class of plasmonic devices. Most importantly, this paper outlines an approach for realizing optimal plasmonic material properties for specific frequencies and applications, thereby providing a reference for those searching for better plasmonic materials.Comment: 27 pages, 6 figures, 2 table

Asymmetry in Charmed Particles Production in Σ−\Sigma^{-} beam

We present the calculation of the inclusive $x_F$-distributions of charmed hadrons, produced in high-energy $\Sigma^-$-beam. The calculation is based on the modified mechanism of charmed quarks fragmentation as well as on the mechanism of $c$-quark recombination with the valence quarks from initial hadrons. We predict the additional asymmetry in the production of charmed hadrons due to the different distributions of the valence s and d quarks in $\Sigma^-$-beam.Comment: 19 pages, Latex, 6 figure