Biomedical subjects

Andreas A Werdich

Publications and source records attributed to Andreas A Werdich.

4 recordsLinked to original sources

PubMed2007

Polymorphic ventricular tachycardia and abnormal Ca2+ handling in very-long-chain acyl-CoA dehydrogenase null mice.

Patients with mutations in the mitochondrial very-long-chain acyl-CoA dehydrogenase (VLCAD) gene are at risk for cardiomyopathy, myocardial dysfunction, ventricular tachycardia (VT), and sudden cardiac death. The mechanism is not known. Here we report a novel mechanism of VT in mice lacking VLCAD (VLCAD(-/-)). These mice exhibited polymorphic VT and increased incidence of VT after isoproterenol infusion. Polymorphic VT was induced in 10 out of 12 VLCAD(-/-) mice (83%) when isoproterenol was used. One out of 10 VLCAD(-/-) mice with polymorphic VT had VT with the typical bidirectional morphology. At the molecular level, VLCAD(-/-) cardiomyocytes showed increased levels of cardiac ryanodine receptor 2, phospholamban, and calsequestrin with increased [(3)H]ryanodine binding in heart microsomes. At the single cardiomyocyte level, VLCAD(-/-) cardiomyocytes showed significant increase in diastolic indo 1 and fura 2 fluorescence, with increased Ca(2+) transient amplitude. These changes were associated with altered Ca(2+) dynamics, to include: faster sarcomere contraction, larger time derivative of the upstroke, and shorter time-to-minimum sarcomere length compared with VLCAD(+/+) control cells. The L-type Ca(2+) current characteristics were not different under voltage-clamp conditions in the two VLCAD genotypes. Sarcoplasmic reticulum Ca(2+) load measured as normalized integrated Na(+)/Ca(2+) exchange current after rapid caffeine application was increased by 48% in VLCAD(-/-) cells. We conclude that intracellular Ca(2+) handling represents a possible molecular mechanism of arrhythmias in mice and perhaps in VLCAD-deficient humans.

Acyl-CoA Dehydrogenase, Long-Chain↗

PubMed2006

Differential pH measurements of metabolic cellular activity in nl culture volumes using microfabricated iridium oxide electrodes.

In this paper we describe a new approach to measure pH differences in microfluidic devices and demonstrated acidification rate measurements in on-chip cell culture systems with nl wells. We use two miniaturized identical iridium oxide (IrOx) thin film electrodes (20 micromx400 microm), one as a quasi-reference electrode, the other as a sensing electrode, placed in two confluent compartments on chip. The IrOx electrodes were deposited onto microfabricated platinum (Pt) electrodes simultaneously using electrodeposition. Incorporating the electrodes into a microfluidic device allowed us to expose each electrode to a different solution with a pH difference of one pH unit maintaining a confluent connection between the electrodes. In this configuration, we obtained a reproducible voltage difference between the two IrOx thin film electrodes, which corresponds to the electrode sensitivities of -70 mV/pH at 22 degrees C. In order to measure the acidification rate of cells in nl cell culture volumes we placed one IrOx thin film electrode in the perfusion channel as a quasi-reference electrode and the other in the cell culture volume. We obtained an acidification rate of 0.19+/-0.02 pH/min for fibroblast cells using a stop flow protocol. These results show that we can use two identical miniaturized microfabricated IrOx electrodes to measure pH differences to monitor the metabolic activity of cell cultures on chip. Furthermore, our approach can also be applied in biosensor or bioanalytical applications.

Animals↗

PubMed2004

Thin-film IrOx pH microelectrode for microfluidic-based microsystems.

Microsensors are valuable tools to monitor cell metabolism in cell culture volumes. The present research describes the fabrication and characterization of on-chip thin-film iridium oxide pH microsensors with dimensions of 20 microm x 20 microm and 20 microm x 40 microm suitable to be incorporated into nl volumes. IrOx thin films were formed on platinum microelectrodes by electrochemical deposition in galvanostatic mode. Anodically grown iridium oxide films showed a near super-Nernstian response with a slope of -77.6+/-2 mV/pH at 22 degrees C, and linear responses within the pH range of 4-11. Freshly deposited electrodes showed response times as low as 6s. Long-term studies showed a baseline drift of 2-3 mV/month, which could easily be compensated by calibration. This work demonstrated for the first time the use of planar IrOx pH microelectrodes to measure the acidification rate of CHO and fibroblast cells in an on chip cell culture volume of 25 nl with microfluidic control.

Animals↗

PubMed2004

A microfluidic device to confine a single cardiac myocyte in a sub-nanoliter volume on planar microelectrodes for extracellular potential recordings.

A hybrid chip is described which combines a microfluidic network fabricated in a silicone elastomer (PDMS) with planar microelectrodes. It was used to measure extracellular potentials from single adult murine cardiac myocytes in a restricted extracellular space. The recorded variations in the extracellular potentials were caused by transmembrane currents associated with spontaneously initiated intracellular calcium waves. Single cells were trapped inside the 100 pl microchamber by pressure gradients and maintained for several hours by continuous perfusion. In addition, the localized delivery of drugs to a portion of the cell was demonstrated. The impedance of the electrodes was reduced by a factor of 10 to 20 after the electrodeposition of platinum black. Biopotentials recorded from single cells with platinum black electrodes showed a three-fold decrease in the noise, resulting in a maximum signal-to-noise ratio of 15:1. Characteristic variations in the frequency and shape of the extracellular potentials were observed among different cells which are most likely due to differences in the sarcoplasmic reticulum Ca(2+) load. Our device architecture permits the integration of electrochemical and optical sensors for multiparameter recordings.

Animals↗