Biomedical subjects

Dirk Isbrandt

Publications and source records attributed to Dirk Isbrandt.

4 recordsLinked to original sources

PubMed2003

Pacemaker channel dysfunction in a patient with sinus node disease.

The cardiac pacemaker current I(f) is a major determinant of diastolic depolarization in sinus nodal cells and has a key role in heartbeat generation. Therefore, we hypothesized that some forms of "idiopathic" sinus node dysfunction (SND) are related to inherited dysfunctions of cardiac pacemaker ion channels. In a candidate gene approach, a heterozygous 1-bp deletion (1631delC) in exon 5 of the human HCN4 gene was detected in a patient with idiopathic SND. The mutant HCN4 protein (HCN4-573X) had a truncated C-terminus and lacked the cyclic nucleotide-binding domain. COS-7 cells transiently transfected with HCN4-573X cDNA indicated normal intracellular trafficking and membrane integration of HCN4-573X subunits. Patch-clamp experiments showed that HCN4-573X channels mediated I(f)-like currents that were insensitive to increased cellular cAMP levels. Coexpression experiments showed a dominant-negative effect of HCN4-573X subunits on wild-type subunits. These data indicate that the cardiac I(f) channels are functionally expressed but with altered biophysical properties. Taken together, the clinical, genetic, and in vitro data provide a likely explanation for the patient's sinus bradycardia and the chronotropic incompetence.

Aged↗

PubMed2002

Identification and functional characterization of a novel KCNE2 (MiRP1) mutation that alters HERG channel kinetics.

Long-QT syndrome (LQTS) may cause syncope and sudden death due to cardiac tachyarrhythmia. Chromosome 7-linked LQTS (LQT2) has been correlated with mutations in the human ether-a-go-go-related gene (HERG). HERG forms voltage-gated K channels that may be associated with Mink-related peptide 1 (MiRP1), an auxiliary beta-subunit. The channels mediate currents that resemble native I(Kr). Mutations in the KCNE2 gene encoding MiRP1 may also cause LQTS. In this study, the frequency of mutations in KCNE2 of 150 unrelated LQTS patients without known genotype and of 100 controls was analyzed using single-strand conformation polymorphism analysis and direct sequencing. We identified a novel missense mutation, V65 M, in the KCNE2 gene of a 17-year-old female with syncope and LQTS. Expression studies in Chinese hamster ovary cells revealed that mutant and wild-type MiRP1 co-localized with HERG subunits and formed functional channels. However, mutant HERG/MiRP1(V65M) channels mediated currents with an accelerated inactivation time course compared with wild-type channels. The accelerated inactivation time course of HERG/MiRP1(V65M) channels may decrease I(Kr) current density of myocardial cells, thereby impairing the ability of myocytes to repolarize in response to sudden membrane depolarizations such as extrasystoles.

Animals↗

PubMed2002

Activation of GABA(A) receptors by guanidinoacetate: a novel pathophysiological mechanism.

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessively inherited disorder of creatine biosynthesis. The disease occurs in early life with developmental delay or arrest and several neurological symptoms, e.g., seizures and dyskinesia. Both the deficiency of high-energy phosphates in neurons and the neurotoxic action of the accumulated metabolite guanidinoacetate (GAA) are candidate mechanisms for the pathophysiology of this disease. To examine a potential role of GAA accumulation, we analyzed the electrophysiological responses of neurons induced by GAA application in primary culture and acute murine brain slices. GAA evoked picrotoxin- and bicuculline-sensitive GABA(A) receptor-mediated chloride currents with an EC(50) of 167 microM in cortical neurons. Pathophysiologically relevant GAA concentrations hyperpolarized globus pallidus neurons and reduced their spontaneous spike frequency with an EC(50) of 15.1 microM. Furthermore, GAA acted as a partial agonist at heterologously expressed GABA(A) but not GABA(B) receptors. The interaction of GAA with neuronal GABA(A) receptors represents a candidate mechanism explaining neurological dysfunction in GAMT deficiency.

Animals↗

PubMed2002

UM 9(5)h and UM 9(5)p, human and porcine noncoding transcripts with preferential expression in the cerebellum.

We compared the gene expression patterns of fetal and adult porcine brains and identified a sequence tag that was more abundant in adult than in fetal brain. The RNA corresponding to the sequence tag has the highest expression level in adult cerebellum. Lower expression levels of the transcript were found in adult cerebrum, pituitary, and uterus, as well as in fetal brain, heart, intestine, kidney, and liver. The sequence tag was used to screen a cDNA library from adult porcine brain. Two independent clones of 2,273 nt and 1,701 nt were isolated. The shorter cDNA is a 5'-truncated form of the longer clone, and both clones have almost identical sequences with multiple start and stop codons in all three reading frames. Screening of two different human brain cDNA libraries with porcine cDNA probes resulted in four overlapping cDNA fragments, which were assembled to one contig of 2,336 nt in length. Like noncoding RNAs, the porcine and human sequences have no common conserved open reading frame and share stretches of high homology interrupted by stretches with almost no homology. The human and porcine RNAs were named UM 9(5)h and UM 9(5)p, respectively. They are part of larger transcripts, which are transcribed from single-copy genes, they have very similar tissue distributions, and their sequences are colinear with the respective genomic fragment.

Animals↗