Biomedical subjects

H L Kanter

Publications and source records attributed to H L Kanter.

11 recordsLinked to original sources

PubMed1995

Structural and molecular determinants of intercellular coupling in cardiac myocytes.

Electrical activation of the heart requires intercellular transfer of current through gap junctions connecting individual cardiac myocytes. Using a combination of light and electron microscopic techniques and molecular approaches, we have characterized the number, size, and spatial distribution of intercellular connections at gap junctions in cardiac myocytes and have also cloned, sequenced, and elucidated the subcellular distribution of three physiologically distinct gap junction channel proteins. In this review, we present evidence to suggest that the spatial distribution of myocyte interconnections and the molecular composition of gap junction channels may confer distinct conduction properties on specific tissues of the mammalian heart such as atrial and ventricular myocardium, and the nodes and bundles of the cardiac conduction system.

Animals↗

PubMed1995

The molecular basis of anisotropy: role of gap junctions.

Electrical activation of the heart requires transfer of current from one discrete cardiac myocyte to another, a process that occurs at gap junctions. Recent advances in knowledge have established that, like most differentiated cells, individual cardiac myocytes express multiple gap junction channel proteins that are members of a multigene family of channel proteins called connexins. These proteins form channels with unique biophysical properties. Furthermore, functionally distinct cardiac tissues such as the nodes and bundles of the conduction system and atrial and ventricular muscle express different combinations of connexins. Myocytes in these tissues are interconnected by gap junctions that differ in tissue-specific manner in terms of their number, size, and three-dimensional distribution. These observations suggest that both molecular and structural aspects of gap junctions are critical determinants of the anisotropic conduction properties of different cardiac tissues. Expression of multiple connexins also creates the possibility that "hybrid" channels composed of more than one connexin protein type can form, thus greatly increasing the potential for fine control of intercellular ion flow and communication within the heart.

Anisotropy↗

PubMed1994

Molecular cloning of two human cardiac gap junction proteins, connexin40 and connexin45.

Intercellular coupling of cardiac myocytes through gap junction channels facilitates normal cardiac impulse conduction. Multiple gap junction sequences (connexins) have been previously identified in mammalian and avian heart, but only one, connexin43 (Cx43), has been identified in the human heart. We used the polymerase chain reaction and genomic cloning to isolate DNA encoding the gap junction proteins human connexin40 (Cx40) and connexin45 (Cx45). Northern blots showed that specific probes for Cx43, Cx40 and Cx45 all hybridize to distinct mRNAs in human ventricular RNA. Immunohistochemistry with connexin-specific antibodies confirmed that Cx40, Cx43, and Cx45 all localized to intercalated disk regions in frozen sections of human left ventricle. The presence of multiple connexins in human ventricle may contribute to divergent mechanisms of regulation of cardiac conduction.

Amino Acid Sequence↗

PubMed1994

Distinct gap junction protein phenotypes in cardiac tissues with disparate conduction properties.

OBJECTIVES: We sought to characterize the connexin phenotypes of selected regions of the canine heart with different conduction properties to determine whether variations in connexin expression might contribute to the differences in intercellular resistance and conduction velocity that occur in different cardiac tissues. BACKGROUND: Gap junctions connect cardiac myocytes, allowing propagation of action potentials. Intercellular channels with different electrophysiologic properties are formed by different connexin proteins. METHODS: To determine which connexins were likely to be expressed in the sinus node, atrioventricular (AV) node and atrial and ventricular myocardium, messenger ribonucleic acids (RNAs) from each of these sites were hybridized with probes for connexin26, connexin31, connexin32, connexin37, connexin40, connexin43, connexin45, connexin46 and connexin50. Immunostaining with monospecific antibodies to connexin40, connexin43 and connexin45 was used to delineate the distribution of connexins in frozen sections of these different cardiac tissues. RESULTS: Only messenger RNAs coding for connexin40, connexin43 and connexin45 were detected by Northern blot analysis. By immunohistochemical staining, junctions in the sinus and AV nodes and proximal His bundle were virtually devoid of connexin43 but contained both connexin40 and connexin45. Gap junctions in the distal His bundle and the proximal bundle branches stained intensely for connexin40 and connexin43 and to a lesser extent for connexin45. Atrial gap junctions showed abundant staining of connexin43, connexin40 and connexin45. Ventricular gap junctions were characterized by abundant staining of connexin43 and connexin45 and much less staining of connexin40. CONCLUSIONS: Although most cardiac gap junctions contain connexin40, connexin43 and connexin45, the relative amounts of each of these connexins vary considerably in cardiac tissues with different conduction properties.

Animals↗

PubMed1994

Relation of regional function, perfusion, and metabolism in patients with advanced coronary artery disease undergoing surgical revascularization.

BACKGROUND: Imaging of myocardial glucose metabolism using [18F]fluorodeoxyglucose (FDG) with positron emission tomography (PET) has been proposed for identification of tissue viability in patients with advanced coronary artery disease. This study was designed to evaluate the predictive value of flow and metabolic imaging for functional recovery after revascularization in myocardial segments of varying degrees of dysfunction. METHODS AND RESULTS: Thirty-seven patients (mean age, 59 +/- 11 years) with coronary artery disease and impaired left ventricular function (ejection fraction, 34 +/- 10%) were studied with PET using FDG and [13N]ammonia before surgical coronary revascularization (3 +/- 1 grafts per patient). Tissue was scintigraphically characterized as normal, nonviable (concordant reduction of perfusion and FDG uptake), viable without discordance of perfusion and metabolism (mildly reduced perfusion and metabolism), or ischemically compromised (mismatch of reduced perfusion and maintained FDG uptake). Functional outcome was assessed by serial radionuclide ventriculography before and at 13 +/- 13 weeks (median interval of 8 weeks) after coronary revascularization. Preoperatively impaired regional wall motion improved significantly in ischemically compromised (mismatch) revascularized segments but not in nonviable myocardium or in viable myocardium without discordance of perfusion and metabolism. The negative predictive value of PET for functional recovery was 86%, whereas the positive predictive value in revascularized regions ranged from 48% to 86% depending on severity of baseline wall motion abnormalities. CONCLUSIONS: PET identifies metabolically active tissue, which benefits from revascularization. Although the negative predictive value of PET for recovery was high, functional improvement of viable but ischemically compromised tissue was less frequent than previously reported. The predictive value of PET was highest in left ventricular segments with severe dysfunction and a mismatch or reduced perfusion but preserved metabolism. Integration of PET, angiographic, and functional data is necessary for the optimal selection of patients with advanced coronary artery disease and impaired left ventricular function for revascularization.

Adult↗

PubMed1994

Tissue-specific determinants of anisotropic conduction velocity in canine atrial and ventricular myocardium.

Electrical conduction is very rapid and highly anisotropic in atrial fiber bundles, such as the crista terminalis. In contrast to left ventricular myocardium in which the ratio of longitudinal to transverse conduction velocities is approximately 3, propagation velocity in the crista terminalis is approximately 10 times greater in the longitudinal than in the transverse direction. To elucidate potential determinants of these distinct conduction properties, we characterized structural and molecular features of intercellular coupling in the crista terminalis and left ventricular myocardium of the canine heart. Analysis of the number and spatial orientation of myocyte interconnections at gap junctions revealed that a typical left ventricular myocyte was connected to 11.3 +/- 2.2 other myocytes. Approximately equal numbers of connections occurred between ventricular myocytes juxtaposed in side-to-side and end-to-end orientation. In contrast, a typical myocyte of the crista terminalis was connected to only 6.4 +/- 1.7 other cells (P < .05), but nearly 80% of these connections occurred between cells oriented in an end-to-end configuration. In comparison with the ventricular pattern, this spatial distribution of connections would limit intercellular current transfer between laterally apposed cells and thereby enhance anisotropy of conduction velocity in the longitudinal and transverse directions. Ultrastructural analysis showed that crista terminalis myocytes were connected by numerous small gap junctions that occurred in relatively simple, straight intercalated disks. Northern blot analysis showed approximately equivalent amounts of mRNAs encoding the gap junction channel proteins connexin43 and connexin45 but approximately four times more connexin40 mRNA in crista terminalis than in the left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Distinct patterns of connexin expression in canine Purkinje fibers and ventricular muscle.

Electrical conduction is more rapid in Purkinje fibers than in ventricular muscle, which are distinct cardiac tissues that have different active and passive electrophysiological properties. We have recently demonstrated that canine myocardium contains multiple gap junction proteins or connexins that form channels with unique electrophysiological properties. To determine whether differences in connexin expression may account, in part, for the characteristic conduction properties of Purkinje fibers and ventricular muscle, we assessed the amounts of mRNA for two connexins, Cx40 and Cx43, in these tissues obtained from canine hearts by Northern blot analysis and in situ hybridization. We also characterized the distribution and relative abundance of these two connexins in gap junctions with immunocytochemistry. A significantly greater amount of Cx40 mRNA was observed in Purkinje fibers compared with ventricular muscle, a difference that was at least threefold according to quantitative in situ hybridization (p < 0.001) and densitometric analysis of Northern blots. Purkinje fibers also demonstrated greater immunostaining intensity when incubated with anti-Cx40 antibodies than did ventricular muscle. In contrast, Cx43 mRNA and protein appeared to be abundant in both tissues. Quantitative in situ hybridization demonstrated a modest but not statistically significant increase in Cx43 mRNA in Purkinje fibers compared with ventricular myocardium. These results indicate that Purkinje fibers and ventricular muscle express distinct patterns of connexins. This tissue-specific pattern of connexin expression could contribute to differences in the conduction properties of Purkinje fibers and ventricular muscle.

Animals↗

PubMed1993

Multiple connexins colocalize in canine ventricular myocyte gap junctions.

We have recently shown that adult canine ventricular myocytes express three distinct gap junction channel proteins, connexin40 (Cx40), connexin43 (Cx43), and connexin45 (Cx45). These proteins have unique cytoplasmic domains that likely confer connexin-specific physiological properties. To determine whether the three distinct channel proteins are distributed in identical or different populations of gap junctions, we performed double-label immunofluorescence on disaggregated canine ventricular myocytes incubated simultaneously with a mouse monoclonal anti-Cx43 and affinity-purified polyclonal rabbit antibodies against Cx40 or Cx45. Analysis of double-labeled cardiac myocytes using laser scanning confocal microscopy revealed virtually identical patterns of immunoreactivity for both the Cx43/Cx40 and Cx43/Cx45 pairs. Double-label immunoelectron microscopy confirmed that ultrastructurally identified cardiac myocyte gap junctions contain multiple channel proteins. Thus, three channel proteins colocalize in canine cardiac myocyte gap junctions. The presence of multiple functionally distinct connexins suggests complex possibilities regarding the composition of individual channels and the regulation of intercellular coupling.

Animals↗

PubMed1992

Molecular cloning and expression of rat connexin40, a gap junction protein expressed in vascular smooth muscle.

Gap junctions contain intercellular channels which are formed by members of a group of related proteins called connexins. Connexins contain conserved transmembrane and extracellular domains, but unique cytoplasmic regions which may provide connexin-specific physiologic properties. We used polymerase chain reaction (PCR) amplification and cDNA library screening to clone DNA encoding a novel member of this gene family, rat connexin40 (Cx40). The derived rat Cx40 polypeptide contains 356 amino acids, with a predicted molecular mass of 40,233 Da. Sequence comparisons suggest that Cx40 is the mammalian homologue of chick connexin42, but it has predicted cytoplasmic regions that differ from previously described mammalian connexins. Southern blots of rat genomic DNA suggest that Cx40 is encoded by a single copy gene containing no introns within its coding region. Northern blots demonstrate that Cx40 is expressed in multiple tissues (including lung, heart, uterus, ovary, and blood vessels) and in primary cultures and established lines of vascular smooth muscle cells. Cx40 is coexpressed with connexin43 in several cell types, including A7r5 cells, which contain two physiologically distinct gap junctional channels. To demonstrate that Cx40 could form functional channels, we stably transfected communication-deficient Neuro2A cells with Cx40 DNA. These Cx40-transfected cells showed intercellular passage of microinjected Lucifer yellow CH. The expression of multiple connexins (such as Cx40 and Cx43) by a single cell may provide a mechanism by which cells regulate intercellular coupling through the formation of multiple channels.

Amino Acid Sequence↗

PubMed1992

Clinical outcome of patients with advanced coronary artery disease after viability studies with positron emission tomography.

OBJECTIVE: The aim of this study was to determine the prognostic significance of perfusion-metabolism imaging in patients undergoing positron emission tomography for myocardial viability assessment. BACKGROUND: Positron emission tomography using nitrogen-13 ammonia and 18fluorodeoxyglucose to assess myocardial blood flow and metabolism has been shown to predict improvement in wall motion after coronary artery revascularization. The prognostic implications of metabolic imaging in patients with advanced coronary artery disease have not been investigated. METHODS: Eighty-two patients with advanced coronary artery disease and impaired left ventricular function underwent positron emission tomographic imaging between August 1988 and March 1990 to assess myocardial viability before coronary artery revascularization. RESULTS: Forty patients underwent successful revascularization. Patients who exhibited evidence of metabolically compromised myocardium by positron emission tomography (decreased blood flow with preserved metabolism) who did not undergo subsequent revascularization were more likely to experience a myocardial infarction, death, cardiac arrest or late revascularization due to development of new symptoms than were the other patient groups (p less than 0.01). Concordantly decreased flow and metabolism in segments of previous infarction did not affect outcome in patients with or without subsequent revascularization. Those with a compromised myocardium who did undergo revascularization were more likely to experience an improvement in functional class than were patients with preoperative positron emission tomographic findings of concordant decrease in flow and metabolism. CONCLUSIONS: Positron emission tomographic myocardial viability imaging appears to identify patients at increased risk of having an adverse cardiac event or death. Patients with impaired left ventricular function and positron emission tomographic evidence for jeopardized myocardium appear to have the most benefit from a revascularization procedure.

Aged↗

PubMed1992

Cardiac myocytes express multiple gap junction proteins.

Electrical propagation in the normal heart occurs via intercellular transfer of current at gap junctions. Alterations in intercellular coupling in the diseased heart are critical in the pathogenesis of reentrant ventricular arrhythmias. Until recently only a single gap junction protein was known to couple cardiac myocytes. We have now identified and sequenced two additional distinct gap junction proteins (connexins) expressed in the mammalian heart. The sequences differ in their predicted cytoplasmic regulatory domains. Expression of all three connexins by canine ventricular myocytes has been confirmed by Northern blotting and by immunohistochemistry with connexin-specific antisera. Immunoelectron microscopy confirmed that all three connexins are localized to myocyte gap junctions. The presence of multiple connexins in myocyte gap junctions suggests novel mechanisms for regulating cardiac electrical coupling.

Animals↗