Low Cost Embedded Copper Mesh Based on Cracked Template for Highly Durability Transparent EMI Shielding Films

Embedded copper mesh coatings with low sheet resistance and high transparency were formed using a low-cost Cu seed mesh obtained with a magnetron sputtering on a cracked template, and subsequent operations electroplating and embedding in a photocurable resin layer. The influence of the mesh size on the optoelectric characteristics and the electromagnetic shielding efficiency in a wide frequency range is considered. In optimizing the coating properties, a shielding efficiency of 49.38 dB at a frequency of 1 GHz, with integral optical transparency in the visible range of 84.3%, was obtained. Embedded Cu meshes have been shown to be highly bending stable and have excellent adhesion strength. The combination of properties and economic costs for the formation of coatings indicates their high prospects for practical use in shielding transparent objects, such as windows and computer monitors.     

Potentiation of Ca(2+) release by cADP-ribose in the heart is mediated by enhanced SR Ca(2+) uptake into the sarcoplasmic reticulum

cADP-Ribose (cADPR) is a novel endogenous messenger that is believed to mobilize Ca(2+) from ryanodine-sensitive Ca(2+) stores. Despite intense research, the precise mechanism of action of cADPR remains uncertain, and experimental findings are contradictory. To elucidate the mechanism of cADPR action, we performed confocal Ca(2+) imaging in saponin-permeabilized rat ventricular myocytes. Exposure of the cells to cADPR resulted in a slow (>2 minutes) and steady increase in the frequency of Ca(2+) sparks. These effects on local release events were accompanied by a significant increase in sarcoplasmic reticulum (SR) Ca(2+) content. In comparison, sensitization of ryanodine receptors (RyRs) by caffeine, a true RyR agonist, caused a rapid (<1 second) and transient potentiation of Ca(2+) sparks followed by a decrease in SR Ca(2+) content. When the increase in the SR load was prevented by partial inhibition of the SR Ca(2+) with thapsigargin, cADPR failed to produce any increase in sparking activity. cADPR had no significant impact on activity of single cardiac RyRs incorporated into lipid bilayers. However, it caused a significant increase in the rate of Ca(2+) uptake by cardiac SR microsomes. Our results suggest that the primary target of cADPR is the SR Ca(2+) uptake mechanism. Potentiation of Ca(2+) release by cADPR is mediated by increased accumulation of Ca(2+) in the SR and subsequent luminal Ca(2+)-dependent activation of RyRs.     

Distribution of ryanodine receptors in rat ventricular myocytes

Ryanodine receptors (RyRs) are the major ion channels in the sarcoplasmic reticulum responsible for Ca²⁺ release in muscle cells. Localization of RyRs is therefore critical to our understanding of Ca²⁺ cycling and Ca²⁺-dependent processes within ventricular cells. Recently, RyRs were reportedly found in non-classical locations in the middle of the sarcomere, between perinuclear mitochondria and in the inner mitochondrial membrane of cardiac mitochondria. However, for multiple reasons these reports could not be considered conclusive. Therefore, we modified immunogold labeling to visualize the distribution of RyRs in ventricular myocytes. Using antibodies to the voltage-dependent anion channel (i.e. VDAC) or cytochrome c along with our labeling method, we showed that these mitochondrial proteins were appropriately localized to the mitochondrial outer and inner membrane respectively. Immunogold labeling of ultrathin sections of intact and permeabilized ventricular myocytes with antibodies to three types of RyRs confirmed the existence of RyRs between the Z-lines and around the perinuclear mitochondria. However, we did not find any evidence to support localization of RyRs to the mitochondrial inner membrane.     

Development of muscle-specific features in cultured frog embryonic skeletal myocytes

To study the development of muscle-specific features during myogenesis, we analysed the ultrastructure and voltage-dependent currents of frog embryonic skeletal myocytes maintained in culture for 10 days. The cells were maintained under culture conditions that prevented cell division, fusion and cell contacts with neuroblasts. The cell surface was estimated morphometrically and from cell capacity and the values obtained were used to calculate ion current densities. It was shown that the expression of all main types of voltage dependent ionic currents occurs during the first 3–5 days. Na⁺ maximum specific conductance at days 1–2 was low but by day 7 it showed a 20-fold increase. The magnitude of Na⁺ current densities increased 16-fold from day 1 (3.6 A/cm) to the day 7 (58.1 A/cm). The maximum specific K⁺ conductance increased almost 3-fold during the first 5 days. In contrast to the other types of currents, I_K undergoes qualitative changes. Sodium action potentials, whose amplitude and time course depend on g_Na/g_K ratio, appeared from day 4 in culture, when myofibrils and the T-system also developed. The amplitude of DHP-sensitive slow I_Ca increased in parallel with the development of the T-membrane. I_Ca,S density per unit of T-membrane area reached an equilibrium of ca., 17 A/cm² on the day 4 and then remained stable until the end of the period of observation. These studies demonstrate that muscle-specific characteristics including morphology and excitatory properties begin to develop on the third day and resemble those of adult muscle cells by the sixth day in culture.     

Regulation of calcium release by calcium inside the sarcoplasmic reticulum in ventricular myocytes

 To study the effects of changes in sarcoplasmic reticulum (SR) intraluminal Ca²⁺ on the Ca²⁺ release mechanism, we correlated the activity of single cardiac ryanodine receptor (RyR) channels, monitored in planar bilayers, with the properties of spontaneous elementary Ca²⁺ release events (sparks) in intact ventricular myocytes, monitored by scanning confocal microfluorimetry. Under both normal conditions and Ca²⁺ overload, induced by elevation of extracellular [Ca²⁺], Ca²⁺ sparks represented single populations of events. During Ca²⁺ overload, the frequency of sparks increased from 0.8 to 3.1 events per second per 100 μm line scanned, and their amplitude increased from 100 nM to 400 nM. The duration of the Ca²⁺ sparks, however, was not altered. Changes in the properties of Ca²⁺ sparks were accompanied by only an ≈ 30% increase in the SR Ca²⁺ content, as determined by emptying the intracellular Ca²⁺ stores using caffeine. When single Ca²⁺ release channels were incorporated into lipid bilayers and activated by cytoplasmic Ca²⁺ (≈ 100 nM) and ATP (3 mM), elevation of Ca²⁺ on the luminal side from 20 μM to 0.2–20 mM resulted in a 1.2-fold to 7-fold increase, respectively, in open probability (P _o). This potentiation of P _o was due to an increase in mean open time and frequency of events. The relative effect of luminal Ca²⁺ was greater at low levels of cytoplasmic [Ca²⁺] than at high levels of cytoplasmic [Ca²⁺], and no effect of luminal Ca²⁺ was observed to occur in channels activated by 0.5–50 μM cytoplasmic Ca²⁺ in the absence of ATP. Our results suggest that SR Ca²⁺ release channels are modulated by SR intraluminal Ca²⁺. These alterations in properties of release channels may account for, or contribute to, the mechanism of spontaneous Ca²⁺ release in cardiac myocytes Received: 15 May 1996 / Received after revision: 5 June 1996 / Accepted: 8 July 1996