Biomedical subjects

António Guia

Publications and source records attributed to António Guia.

4 recordsLinked to original sources

PubMed2006

Efficient characterization of use-dependent ion channel blockers by real-time monitoring of channel state.

Ion channels are important therapeutic targets for the treatment of a variety of conditions. Among ion channel blocking agents, use-dependent inhibitors can be especially effective therapeutic agents. Use dependence allows the selective inhibition of hyperactive neurons or tachycardiac myocytes, while minimizing effects on cells with normal activity. For voltage-gated channels, the use-dependent compounds typically bind to and inhibit a particular kinetic state that is induced by specific voltage changes. Drug discovery programs that focus on this class of drugs need to rank the use dependence of the compounds. A meaningful comparison among different molecules requires voltage clamp-based assays with continuous voltage control and compensation for or elimination of electrode drift-related effects. A method was developed based on automated electrophysiology in which voltage and frequency dependence of voltage-gated ion channel blockers can be compared using a protocol in which voltage error is compensated for in real time.

Carbamazepine↗

PubMed2004

Automated tight seal electrophysiology for assessing the potential hERG liability of pharmaceutical compounds.

Unintended inhibition of the cardiac potassium channel human ether-a-go-go-related gene (hERG) is considered the main culprit in drug-induced arrhythmias known as torsades de pointes. Electrophysiology is the most reliable in vitro screening method for identifying potential cardiac hERG liabilities, but only the recent advent of planar electrode-based voltage clamp electrophysiology promises sufficient throughput to support the drug testing needs of most drug discovery programs. We have assessed the reliability of this new format of the voltage clamp technology in measuring the activity of small molecules on the hERG channel. Based on the results herein of a screening against a panel of well-characterized hERG-active and -inactive molecules, we demonstrate that planar electrode electrophysiology, utilizing the Sealchip and PatchXpress technology platform (AVIVA Biosciences Corp., San Diego, CA), is comparable to traditional electrophysiology based on glass micropipettes in its reliability and data content. The new technology will allow significantly higher throughput and more thorough testing of pharmaceutical compounds.

Amiodarone↗

PubMed2003

A benchmark study with sealchip planar patch-clamp technology.

Although conventional patch-clamp methods provide high information content, they are labor-intensive and suffer from low throughput and high overall cost. Several approaches for achieving high throughput electrophysiology are under development, among which microchip-based patch-clamp systems uniquely achieve a higher degree of miniaturization, faster perfusion and mixing, and lower reagent cost without losing information content. The goal of this study was to establish a benchmark for our biochip technology with 52 chips tested sequentially. We demonstrate that our microfabrication and processing technology is sufficiently mature to produce a consistent hole size. We further demonstrate high-quality planar whole-cell patch clamping with >75% overall success rate at achieving gigaohm seals, followed by stable whole-cell access lasting at least 15 min with access resistance (Ra) below 15 MOmega and membrane resistance (Rm) above 200 MOmega. These biochips are ideally suited for high throughput compound screening for ion channel targets.

Animals↗

PubMed2002

Ca(2+) signaling in cardiac myocytes overexpressing the alpha(1) subunit of L-type Ca(2+) channel.

Voltage-gated L-type Ca(2+) channels (LCCs) provide Ca(2+) ingress into cardiac myocytes and play a key role in intracellular Ca(2+) homeostasis and excitation-contraction coupling. We investigated the effects of a constitutive increase of LCC density on Ca(2+) signaling in ventricular myocytes from 4-month-old transgenic (Tg) mice overexpressing the alpha(1) subunit of LCC in the heart. At this age, cells were somewhat hypertrophic as reflected by a 20% increase in cell capacitance relative to those from nontransgenic (Ntg) littermates. Whole cell I(Ca) density in Tg myocytes was elevated by 48% at 0 mV compared with the Ntg group. Single-channel analysis detected an increase in LCC density with similar conductance and gating properties. Although the overexpressed LCCs triggered an augmented SR Ca(2+) release, the "gain" function of EC coupling was uncompromised, and SR Ca(2+) content, diastolic cytosolic Ca(2+), and unitary properties of Ca(2+) sparks were unchanged. Importantly, the enhanced I(Ca) entry and SR Ca(2+) release were associated with an upregulation of the Na(+)-Ca(2+) exchange activity (indexed by the half decay time of caffeine-elicited Ca(2+) transient) by 27% and SR Ca(2+) recycling by approximately 35%. Western analysis detected a 53% increase in the Na(+)-Ca(2+) exchanger expression but no change in the abundance of ryanodine receptor (RyR), SERCA2, and phospholamban. Analysis of I(Ca) kinetics suggested that SR Ca(2+) release-dependent inactivation of LCCs remains intact in Tg cells. Thus, in spite of the modest cardiac hypertrophy, the overexpressed LCCs form functional coupling with RyRs, preserving both orthograde and retrograde Ca(2+) signaling between LCCs and RyRs. These results also suggest that a modest but sustained increase in Ca(2+) influx triggers a coordinated remodeling of Ca(2+) handling to maintain Ca(2+) homeostasis.

Action Potentials↗