Yoram Etzion

Prevascularization of cardiac patch on the omentum improves its therapeutic outcome

The recent progress made in the bioengineering of cardiac patches offers a new therapeutic modality for regenerating the myocardium after myocardial infarction (MI). We present here a strategy for the engineering of a cardiac patch with mature vasculature by heterotopic transplantation onto the omentum. The patch was constructed by seeding neonatal cardiac cells with a mixture of prosurvival and angiogenic factors into an alginate scaffold capable of factor binding and sustained release. After 48 h in culture, the patch was vascularized for 7 days on the omentum, then explanted and transplanted onto infarcted rat hearts, 7 days after MI induction. When evaluated 28 days later, the vascularized cardiac patch showed structural and electrical integration into host myocardium. Moreover, the vascularized patch induced thicker scars, prevented further dilatation of the chamber and ventricular dysfunction. Thus, our study provides evidence that grafting prevascularized cardiac patch into infarct can improve cardiac function after MI.

Experimental studies on a novel roof pond configuration for the cooling of buildings

A new evaporation based passive cooling technology was tested. The technology is based on the exposure of “floating” wetted cloth to the ambient air. It was compared to various other passive cooling techniques, with very favorable results. Two identical shallow ponds were constructed. One of them was covered with white cotton towels stretched on a densely perforated PVC panel supported by pieces of waterproof polystyrene keeping it just floating on the water surface. Five comparable experiments of different cooling techniques have been carried out. The results indicate that the new cooling technique performed slightly better than the pond with movable insulation, which is widely considered as one of the best roof cooling techniques based on evaporation. It seems that the higher efficiency of the tested technique is due to the thermal stratification created in the water inside the pond, which more effectively resists the transfer of heat gains from the sun and ambient air into the deep water of the pond. In turn, the water temperature near the floor of the pond is lower, thus heat flow from the building to the pond is increased. During the experiment, all the ponds which were compared were ranked according to performance (from best to worse): shaded pond with towels floated on it, pond with towels floated on it and pond with movable insulation, shaded open pond, open pond, covered pond.

Molecular Basis for Zinc Transporter 1 Action as an Endogenous Inhibitor of L-type Calcium Channels

The L-type calcium channel (LTCC) has a variety of physiological roles that are critical for the proper function of many cell types and organs. Recently, a member of the zinc-regulating family of proteins, ZnT-1, was recognized as an endogenous inhibitor of the LTCC, but its mechanism of action has not been elucidated. In the present study, using two-electrode voltage clamp recordings in Xenopus oocytes, we demonstrate that ZnT-1-mediated inhibition of the LTCC critically depends on the presence of the LTCC regulatory β-subunit. Moreover, the ZnT-1-induced inhibition of the LTCC current is also abolished by excess levels of the β-subunit. An interaction between ZnT-1 and the β-subunit, as demonstrated by co-immunoprecipitation and by fluorescence resonance energy transfer, is consistent with this result. Using surface biotinylation and total internal reflection fluorescence microscopy in HEK293 cells, we show a ZnT-1-dependent decrease in the surface expression of the pore-forming α1-subunit of the LTCC. Similarly, a decrease in the surface expression of the α1-subunit is observed following up-regulation of the expression of endogenous ZnT-1 in rapidly paced cultured cardiomyocytes. We conclude that ZnT-1-mediated inhibition of the LTCC is mediated through a functional interaction of ZnT-1 with the LTCC β-subunit and that it involves a decrease in the trafficking of the LTCC α1-subunit to the surface membrane.

Potassium currents modulation of calcium spike firing in dendrites of cerebellar Purkinje cells

Abstract The pattern of sustained Ca2+ spike firing was investigated, using macropatch clamp and intracellular recordings, in guinea pig cerebellar Purkinje cells. Under our standard experimental conditions (30°C, 5 mM [K+]o, 2 mM [Ca2+]o, 1 μM tetrodotoxin), each firing period started with uniform firing and gradually turned into a doublet pattern with a large spike afterhyperpolarization (AHP) between the doublets. Macropatch clamp recordings from localized dendritic regions revealed that each doublet is composed of two similar inward current deflections. This result indicated, for both peaks, an active process in the recording site and contradicted the possibility that they reflect firing in two completely separated dendritic regions. When [K+]o was increased the transition to a doublet pattern occurred earlier and the doublets became more pronounced. A similar but more prominent effect occurred following application of 1–10 μM 4-aminopyridine, which also reduced the threshold, increased the spike amplitude, and shortened the initial delay of evoked Ca2+ spike firing. In contrast, membrane depolarization, increased [Ca2+ ]o, and application of quinidine (but not apamine) markedly suppressed the generation of doublet pattern. During uniform initial firing, a short hyperpolarizing pulse that mimicked a large AHP induced a subsequent doublet. A short depolarizing pulse following a single spike induced an artificial doublet followed by a large AHP. These results indicate that the pattern of Ca2+ spike firing in the dendrites of Purkinje cells is dynamically modulated by a highly aminopyridine-sensitive K+ current, and probably also by a Ca2+ -activated potassium current.

Adaptive architecture: integrating low-energy technologies for climate control in the desert

Abstract The article describes a ‘climatically adaptive’ approach to intelligent building in which a variety of technologies are integrated in the architectural design to provide thermal comfort with a minimal expenditure of energy. This concept is illustrated by the design of the Blaustein International Center for Desert Studies, a multi-use complex completed recently at the Sede-Boker Campus of Ben-Gurion University of the Negev. In response to the local climate of this desert region, a number of strategies were developed by the authors to exploit natural energy for heating and cooling: earth berming of major parts of the building, ‘selective glazing’ for seasonal shading and energy collection, a down-draft ‘cool-tower’ for evaporative cooling and a hybrid mechanism for hot-air supply are several of the unique systems whose performance and feasibility are analyzed within the context of the overall building design.

Period Doubling of Calcium Spike Firing in a Model of a Purkinje Cell Dendrite

Recordings from cerebellar Purkinje cell dendrites have revealed that in response to sustained current injection, the cell firing pattern can move from tonic firing of Ca2+ spikes to doublet firing and even to quadruplet firing or more complex firing. These firing patterns are not modified substantially if Na+ currents are blocked. We show that the experimental results can be viewed as a slow transition of the neuronal dynamics through a period-doubling bifurcation. To further support this conclusion and to understand the underlying mechanism that leads to doublet firing, we develop and study a simple, one-compartment model of Purkinje cell dendrite. The neuron can also exhibit quadruplet and chaotic firing patterns that are similar to the firing patterns that some of the Purkinje cells exhibit experimentally. The effects of parameters such as temperature, applied current, and potassium reversal potential in the model resemble their effects in experiments. The model dynamics involve three time scales. Ca2+- dependent K+ currents, with intermediate time scales, are responsible for the appearance of doublet firing, whereas a very slow hyperpolarizing current transfers the neuron from tonic to doublet firing. We use the fast-slow analysis to separate the effects of the three time scales. Fast-slow analysis of the neuronal dynamics, with the activation variable of the very slow, hyperpolarizing current considered as a parameter, reveals that the transitions occurs via a cascade of period-doubling bifurcations of the fast and intermediate subsystem as this slow variable increases. We carry out another analysis, with the Ca2+ concentration considered as a parameter, to investigate the conditions for the generation of doublet firing in systems with one effective variable with intermediate time scale, in which the rest state of the fast subsystem is terminated by a saddle-node bifurcation. We find that the scenario of period doubling in these systems can occur only if (1) the time scale of the intermediate variable (here, the decay rate of the calcium concentration) is slow enough in comparison with the interspike interval of the tonic firing at the transition but is not too slow and (2) there is a bistability of the fast subsystem of the spike-generating variables.

Pressure-induced depression of synaptic transmission in the cerebellar parallel fibre synapse involves suppression of presynaptic N-type Ca2+ channels

High pressure induces CNS hyperexcitability while markedly depressing synaptic transmitter release. We studied the effect of pressure (up to 10.1 MPa) on the parallel fibre (PF) synaptic response in biplanar cerebellar slices of adult guinea pigs. Pressure mildly reduced the PF volley amplitude and to a greater extent depressed the excitatory field postsynaptic potential (fPSP). The depression of the PF volley was noted even at supramaximal stimulus intensities, indicating an effect of pressure on the amplitude of the action potential in each axon. Low concentrations of TTX mimicked the effects of pressure on the PF volley without affecting the fPSP. Application ω‐conotoxin GVIA (ω‐CgTx) reduced the synaptic efficacy by 34.3 ± 2.7%. However, in the presence of ω‐CgTx the synaptic depression at pressure was significantly reduced. Reduced Ca2+ entry by application of Cd2+ or low [Ca2+]o did not have a similar influence on the effects of pressure. Application of ω‐AGA IVA, ω‐AGA TK and Funnel‐web spider toxin did not affect the synaptic response in concentrations that usually block P‐type Ca2+ channels, whilst the N/P/Q‐type blocker ω‐conotoxin MVIIC reduced the response to 52.7 ± 5.0% indicating the involvement of Q‐type channels and R‐type channels in the non‐N‐type fraction of Ca2+ entry. The results demonstrate that N‐type Ca2+ channels play a crucial role in the induction of PF synaptic depression at pressure. This finding suggests a coherent mechanism for the induction of CNS hyperexcitability at pressure.

Analysis and experimental verification of an improved cooling radiator

Roof ponds cooled by nocturnal long wave radiation have often been proposed as a cheap and effective means of providing thermal comfort in buildings in hot-arid locations. Many of the schemes incorporate flat-plate radiators through which the water is circulated at night to be cooled. This paper analyzes the parameters affecting the performance of such a radiator, specifically designed for nocturnal radiative cooling. A cheap, simple and flexible design for a cooling radiator was suggested as a result of the analysis, and tested at the experimental facilities of the Center for Desert Architecture at Sede-Boqer, Israel. The mean nightly cooling output of the radiator - due to the combined effect of radiation and convection - was over 90 watts/m2 under typical desert meteorological conditions. The analytical model adapted for this application allows accurate calculation of the fluid temperature at the outlet of the radiator, as a function of the properties of the radiator, the meteorological conditions and the operating parameters of the cooling system.

ZnT-1 enhances the activity and surface expression of T-type calcium channels through activation of Ras-ERK signaling

Zinc transporter-1 (ZnT-1) is a putative zinc transporter that confers cellular resistance from zinc toxicity. In addition, ZnT-1 has important regulatory functions, including inhibition of L-type calcium channels and activation of Raf-1 kinase. Here we studied the effects of ZnT-1 on the expression and function of T-type calcium channels. In Xenopus oocytes expressing voltage-gated calcium channel (CaV) 3.1 or CaV3.2, ZnT-1 enhanced the low-threshold calcium currents (I(caT)) to 182 ± 15 and 167.95 ± 9.27% of control, respectively (P < 0.005 for both channels). As expected, ZnT-1 also enhanced ERK phosphorylation. Coexpression of ZnT-1 and nonactive Raf-1 blocked the ZnT-1-mediated ERK phosphorylation and abolished the ZnT-1-induced augmentation of I(caT). In mammalian cells (Chinese hamster ovary), coexpression of CaV3.1 and ZnT-1 increased the I(caT) to 166.37 ± 6.37% compared with cells expressing CaV3.1 alone (P < 0.01). Interestingly, surface expression measurements using biotinylation or total internal reflection fluorescence microscopy indicated marked ZnT-1-induced enhancement of CaV3.1 surface expression. The MEK inhibitor PD-98059 abolished the ZnT-1-induced augmentation of surface expression of CaV3.1. In cultured murine cardiomyocytes (HL-1 cells), transient exposure to zinc, leading to enhanced ZnT-1 expression, also enhanced the surface expression of endogenous CaV3.1 channels. Consistently, in these cells, endothelin-1, a potent activator of Ras-ERK signaling, enhanced the surface expression of CaV3.1 channels in a PD-98059-sensitive manner. Our findings indicate that ZnT-1 enhances the activity of CaV3.1 and CaV3.2 through activation of Ras-ERK signaling. The augmentation of CaV3.1 currents by Ras-ERK activation is associated with enhanced trafficking of the channel to the plasma membrane.

Spontaneous Na+ and Ca2+ spike firing of cerebellar Purkinje neurons at high pressure

Abstract The effects of high pressure (up to 10.1 MPa) on the spontaneous firing of Purkinje neurons in guinea-pig cerebellar slices were studied using the macropatch clamp technique. Pressure did not significantly alter the single somatic Na+ spike parameters or the frequency of regular Na+ spike firing. When Na+ currents were blocked by 0.5–1 µM tetrodotoxin (TTX), a pressure of 10.1 MPa slightly reduced the dendritic Ca2+ spike amplitude to 90.2±3.1% of its control value, and slowed its kinetics. The effects of pressure on the single Ca2+ spike were even less prominent when K+ currents were blocked by 5 mM 4-aminopyridine (4-AP). Pressure prolonged the active period of Ca2+ spike firing to 152.2±10.4% of the control value. Within the active period pressure increased the inter-spike interval to 164.9±8.7% and suppressed the typical firing of doublets. The latter changes were reversed by a high extracellular potassium concentration ([K+]o) and 1 µM 4-AP, whereas in the presence of 5 mM 4-AP the pattern was insensitive to pressure. A high [Ca2+]o reduced the firing frequency and suppressed doublet firing in a manner reminiscent of the pressure effect, but these changes could not be reversed by 4-AP. A low [Ca2+]o slightly increased the firing of doublets. These results show that the single somatic Na+ spike is insensitive and the dendritic Ca2+spike is only mildly sensitive to pressure. However, alterations in Ca2+spike firing pattern suggest that modulation of dendritic K+ currents induce depression of dendritic excitability at pressure.