Biomedical subjects

Halina Dobrzynski

Publications and source records attributed to Halina Dobrzynski.

5 recordsLinked to original sources

PubMed2004

Requirement of neuronal- and cardiac-type sodium channels for murine sinoatrial node pacemaking.

The majority of Na+ channels in the heart are composed of the tetrodotoxin (TTX)-resistant (KD, 2-6 microm) Nav1.5 isoform; however, recently it has been shown that TTX-sensitive (KD, 1-10 nm) neuronal Na+ channel isoforms (Nav1.1, Nav1.3 and Nav1.6) are also present and functionally important in the myocytes of the ventricles and the sinoatrial (SA) node. In the present study, in mouse SA node pacemaker cells, we investigated Na+ currents under physiological conditions and the expression of cardiac and neuronal Na+ channel isoforms. We identified two distinct Na+ current components, TTX resistant and TTX sensitive. At 37 degrees C, TTX-resistant iNa and TTX-sensitive iNa started to activate at approximately -70 and approximately -60 mV, and peaked at -30 and -10 mV, with a current density of 22 +/- 3 and 18 +/- 1 pA pF(-1), respectively. TTX-sensitive iNa inactivated at more positive potentials as compared to TTX-resistant iNa. Using action potential clamp, TTX-sensitive iNa was observed to activate late during the pacemaker potential. Using immunocytochemistry and confocal microscopy, different distributions of the TTX-resistant cardiac isoform, Nav1.5, and the TTX-sensitive neuronal isoform, Nav1.1, were observed: Nav1.5 was absent from the centre of the SA node, but present in the periphery of the SA node, whereas Nav1.1 was present throughout the SA node. Nanomolar concentrations (10 or 100 nm) of TTX, which block TTX-sensitive iNa, slowed pacemaking in both intact SA node preparations and isolated SA node cells without a significant effect on SA node conduction. In contrast, micromolar concentrations (1-30 microm) of TTX, which block TTX-resistant iNa as well as TTX-sensitive iNa, slowed both pacemaking and SA node conduction. It is concluded that two Na+ channel isoforms are important for the functioning of the SA node: neuronal (putative Nav1.1) and cardiac Nav1.5 isoforms are involved in pacemaking, although the cardiac Nav1.5 isoform alone is involved in the propagation of the action potential from the SA node to the surrounding atrial muscle.

Action Potentials↗

PubMed2004

Structure-function relationship in the AV junction.

In the normal heart, the atrioventricular node (AVN) is part of the sole pathway between the atria and ventricles. Under normal physiological conditions, the AVN controls appropriate frequency-dependent delay of contractions. The AVN also plays an important role in pathology: it protects ventricles during atrial tachyarrhythmia, and during sinoatrial node failure an AV junctional pacemaker can drive the heart. Finally, the AV junction provides an anatomical substrate for reentry. Using fluorescent imaging with voltage-sensitive dyes and immunohistochemistry, we have investigated the structure-function relationship of the AV junction during normal conduction, reentry, and junctional rhythm. We identified molecular and structural heterogeneity that provides a substrate for the dual-pathway AVN conduction. We observed heterogeneity of expression of three isoforms of connexins: Cx43, Cx45, and Cx40. We identified the site of origin of junctional rhythm at the posterior extension of the AV node in 79% (n = 14) of the studied hearts. This structure was similar to the compact AV node as determined by morphologic and molecular investigations. In particular, both the posterior extension and the compact node express the pacemaking channel HCN4 (responsible for the I(F) current) and neurofilament 160. In the rabbit heart, AV junction conduction, reentrant arrhythmia, and spontaneous rhythm are governed by heterogeneity of expression of several isoforms of gap junctions and ion channels. Uniform neurofilament expression suggests that AV nodal posterior extensions are an integral part of the cardiac pacemaking and conduction system. On the other hand, differential expression of Cx isoforms in this region provides an explanation of longitudinal dissociation, dual-pathway electrophysiology, and AV nodal reentrant arrhythmogenesis.

Animals↗

PubMed2003

Site of origin and molecular substrate of atrioventricular junctional rhythm in the rabbit heart.

During failure of the sinoatrial node, the heart can be driven by an atrioventricular (AV) junctional pacemaker. The position of the leading pacemaker site during AV junctional rhythm is debated. In this study, we present evidence from high-resolution fluorescent imaging of electrical activity in rabbit isolated atrioventricular node (AVN) preparations that, in the majority of cases (11 out of 14), the AV junctional rhythm originates in the region extending from the AVN toward the coronary sinus along the tricuspid valve (posterior nodal extension, PNE). Histological and immunohistochemical investigation showed that the PNE has the same morphology and unique pattern of expression of neurofilament160 (NF160) and connexins (Cx40, Cx43, and Cx45) as the AVN itself. Block of the pacemaker current, If, by 2 mmol/L Cs+ increased the AV junctional rhythm cycle length from 611+/-84 to 949+/-120 ms (mean+/-SD, n=6, P<0.001). Immunohistochemical investigation showed that the principal If channel protein, HCN4, is abundant in the PNE. As well as the AV junctional rhythm, the PNE described in this study may also be involved in the slow pathway of conduction into the AVN as well as AVN reentry, and the predominant lack of expression of Cx43 as well as the presence of Cx45 in the PNE shown could help explain its slow conduction.

Animals↗

PubMed2003

Sophisticated architecture is required for the sinoatrial node to perform its normal pacemaker function.

The heart's pacemaker, the sinoatrial node, does not consist of a group of uniform sinoatrial node cells embedded in atrial muscle. Instead, it is a heterogeneous tissue with multiple cell types and a complex structure. Evidence suggests that from the periphery to the center of the sinoatrial node, there is a gradient in action potential shape, pacemaking, ionic current densities, connexin expression, Ca2+ handling, myofilament density, and cell size. This complexity may be necessary for the sinoatrial node to pacemake under diverse conditions, drive the more hyperpolarized atrial muscle, and resist proarrhythmic perturbations.

Action Potentials↗

PubMed2002

Heterogeneous expression of Ca(2+) handling proteins in rabbit sinoatrial node.

We investigated the densities of the L-type Ca(2+) current, i(Ca,L), and various Ca(2+) handling proteins in rabbit sinoatrial (SA) node. The density of i(Ca,L), recorded with the whole-cell patch-clamp technique, varied widely in sinoatrial node cells. The density of i(Ca,L) was significantly (p<0.001) correlated with cell capacitance (measure of cell size) and the density was greater in larger cells (likely to be from the periphery of the SA node) than in smaller cells (likely to be from the center of the SA node). Immunocytochemical labeling of the L-type Ca(2+) channel, Na(+)-Ca(2+) exchanger, sarcoplasmic reticulum Ca(2+) release channel (RYR2), and sarcoplasmic reticulum Ca(2+) pump (SERCA2) also varied widely in SA node cells. In all cases there was significantly (p<0.05) denser labeling of cells from the periphery of the SA node than of cells from the center. In contrast, immunocytochemical labeling of the Na(+)-K(+) pump was similar in peripheral and central cells. We conclude that Ca(2+) handling proteins are sparse and poorly organized in the center of the SA node (normally the leading pacemaker site), whereas they are more abundant in the periphery (at the border of the SA node with the surrounding atrial muscle).

Animals↗