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Biomedical subjects

David McKinnon

Publications and source records attributed to David McKinnon.

8 recordsLinked to original sources
PubMed2007

Molecular basis of the T- and L-type Ca2+ currents in canine Purkinje fibres.

This study examines the molecular basis for the T-type and L-type Ca(2+) currents in canine Purkinje cells. The I(CaT) in Purkinje cells was completely suppressed by 200 nM kurtoxin, a specific blocker of both Ca(v)3.1 and Ca(v)3.2 channels. Since only Ca(v)3.2 mRNA is expressed at high levels in Purkinje fibres, being approximately 100-fold more abundant than either Ca(v)3.1 or Ca(v)3.3 mRNAs, it is concluded that the Ca(v)3.2 gene encodes the bulk of the T-type Ca(2+) channels in canine Purkinje cells. This conclusion is consistent with the sensitivity of the current to blockade by Ni(2+) ions (K(D) = 32 microM). For L-type channels, Ca(v)1.2 mRNA was most abundant in Purkinje fibres but a significant level of Ca(v)1.3 mRNA expression was also found. A comparison of the sensitivity to blockade by isradipine of the L-type currents in Purkinje cells and ventricular epicardial myocytes, which only express Ca(v)1.2, suggests that the Ca(v)1.3 channels make, at most, a minor contribution to the L-type current in canine Purkinje cells.

Animals↗
PubMed2006

Regional variation in mRNA transcript abundance within the ventricular wall.

Previous studies have shown that regional variation in ion channel gene expression contributes to electrical heterogeneity within the walls of the cardiac ventricles. To map the extent of regional variation in gene expression in the ventricular walls and to begin to understand its genesis we have performed a microarray analysis of gene expression in the epicardial and endocardial tissues of the rat adult left ventricle. While the vast majority of the genes are expressed at uniform levels across the ventricular wall, a total of 36 transcripts (representing less than 0.1% of the genes expressed in the ventricle) are expressed more abundantly in either epicardium or endocardium. One of these differentially expressed genes is the sodium channel gene Scn5a, which is expressed at higher levels in the endocardium than in the epicardium of rat heart. The transcription factor genes Irx3, Irx5 and Etv1 were found to be expressed in transmural gradients across the ventricular wall of rat heart and also of canine heart. The Irx3 and Irx5 genes were expressed in an inverse pattern to that of the Kcnd2 (Kv4.2) gene in rat heart, suggesting that these transcription factors may act as negative regulators of Kcnd2 expression in vivo.

Animals↗
PubMed2005

The cAMP response element binding protein modulates expression of the transient outward current: implications for cardiac memory.

OBJECTIVE: Long-term cardiac memory (LTCM), expressed as a specific pattern of T-wave change on ECG, is associated with 1) reduced transient outward potassium current (I(to)), 2) reduced mRNA for the pore-forming protein of I(to), Kv4.3, 3) reduced cAMP response element binding protein (CREB), and 4) diminished binding to its docking site on the DNA, the cAMP response element (CRE). We hypothesized a causal link between the decrease of the transcription factor CREB and down-regulation of I(to) and one of its channel subunits, KChIP2, in LTCM. METHODS: After three weeks of left ventricular pacing to induce LTCM (8 paced, 7 sham control dogs), epicardial KChIP2 mRNA and protein levels were assessed by real-time PCR and Western blotting. Mimicking the CREB down-regulation in LTCM, CREB was knocked down in situ in other dogs using adenoviral anti-sense. Effects on the action potential notch, reflecting I(to), were investigated in situ using monophasic action potential (MAP) recordings and at the cellular level by the whole-cell patch clamp technique. CREB binding in the KChIP2 promoter region was ascertained by electrophoretic mobility-shift assays. RESULTS: In LTCM, epicardial KChIP2 mRNA and protein were reduced by 62% and 76%, respectively, compared to shams (p < 0.05). CREB binding by the canine KChIP2 promoter region was demonstrated. CREB knockdown led to disappearance of the phase1 notch in MAP and ablation of I(to). CONCLUSIONS: These results strengthen the hypothesis that down-regulation of CREB-mediated transcription underlies the attenuation of epicardial I(to) in LTCM. They also emphasize that ventricular pacing exerts effects at a subcellular level contributing to memory and conceivably to other forms of cardiac remodeling.

Action Potentials↗
PubMed2004

Regulation of ion channel expression.

A potentially important mechanism controlling ion channel expression is homeostatic regulation, which can act to maintain a stable electrophysiological phenotype in cardiac myocytes as well as to provide plasticity in response to genetic, pathological, or pharmacological insults. The capabilities and limitations of the homeostatic regulatory mechanisms that contribute to the control of cardiac ion channel expression are the primary topic of this review.

Animals↗
PubMed2004

Comparison of different probe-level analysis techniques for oligonucleotide microarrays.

Three different software packages for the probe-level analysis of high-density oligonucleotide microarray data were compared using an experiment-derived data set that was validated using real-time PCR. The efficiency with which these three programs could identify true positives in this data set was assessed. In addition, estimates of false-positive and false-negative rates were determined. The performance of the programs using very small data sets was also compared, and recommendations for use are suggested.

Animals↗
PubMed2003

Concordant expression of KChIP2 mRNA, protein and transient outward current throughout the canine ventricle.

Expression of the transient outward K+ current (Ito) was analysed in nine different regions of the canine ventricle. In addition to the previously described transmural gradients in the right and left ventricular free walls, an inverted U-shaped pattern of Ito expression was observed in the interventricular septum. The mRNA and protein expression for the K+ channel beta subunit KChIP2 were examined in the same tissues. The KChIP2 protein levels closely matched mRNA expression in all regions of the ventricle and paralleled the density of Ito. The global pattern of gene expression in human epicardial and endocardial tissue was examined using microarrays. Only 0.1 % of the genes expressed in the human ventricle displayed the same expression pattern as the KChIP2 gene in left ventricle. It is unlikely, therefore, that the reported distribution of KChIP2 protein within the ventricle can be explained by a cross-reaction of the anti-KChIP2 antibody with a different protein. It is concluded that transcriptional regulation of the KChIP2 gene is a primary determinant of Ito expression in heart.

Animals↗
PubMed2003

International Union of Pharmacology. XLI. Compendium of voltage-gated ion channels: potassium channels.

This summary article presents an overview of the molecular relationships among the voltage-gated potassium channels and a standard nomenclature for them, which is derived from the IUPHAR Compendium of Voltage-Gated Ion Channels. The complete Compendium, including data tables for each member of the potassium channel family can be found at http://www.iuphar-db.org/iuphar-ic/.

Phylogeny↗