Expression and regulation of connexins in cultured ventricular myocytes isolated from adult rat hearts

Polontchouk, Lioudmila; Valiūnas, Virginijus; Haefliger, Jacques‐Antoine; Eppenberger, Hans M.; Weingart, Robert

doi:10.1007/s00424-001-0747-z

Cited by 28 publications

(23 citation statements)

References 39 publications

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“…The occurrence of heterotypic and heteromeric gap junction channels is not surprising due to the sequence homology of the different connexins. Because cardiomyocytes can coexpress more than one connexin, the formation of heterotypic and perhaps even heteromeric gap junction channels in vivo is imaginable and strongly assumable from the results of our and other studies examining mammalian cells from primary cell culture (Chen and DeHaan 1996;Elenes et al 1999;Polontchouk et al 2002).…”

Section: Introductionmentioning

confidence: 96%

Neonatal Rat Cardiomyocytes Show Characteristics of Nonhomotypic Gap Junction Channels

Schulte

Scheffler

Rojas-Gómez

et al. 2008

Cell Communication & Adhesion

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Neonatal rat cardiomyocytes mainly coexpress the connexins Cx40, Cx43, and to a small amount Cx45, leading to potential formation of mixed (heteromeric/heterotypic) gap junction channels. Using the dual-voltage clamp technique with switching clamp circuits, the authors investigated voltage sensitivity of gap junction channels between cell pairs of Cx40, Cx43, and Cx45 stably transfected HeLa cells and compared those data to data obtained from cell pairs of cultured neonatal rat cardiomyocytes. In accordance to previously published data, the relationship between normalized conductance and transjunctional voltage (g/V j ) was quasisymmetrical for the transfected HeLa cells, indicating homotypic gap junction channels. Boltzmann curves fitted to data obtained from neonatal rat cardiomyocyte pairs expressing both Cx40 and Cx43 showed an asymmetrical inactivation pattern, which cannot be explained by the presence of pure populations of homotypic gap junction channels of either isoform. In conclusion the authors assume the additional presence of heterotypic and possibly even heteromeric gap junction channels in neonatal rat cardiomyocytes.

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Section: Introductionmentioning

confidence: 96%

Neonatal Rat Cardiomyocytes Show Characteristics of Nonhomotypic Gap Junction Channels

Schulte

Scheffler

Rojas-Gómez

et al. 2008

Cell Communication & Adhesion

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“…29 LY transits a connexin channel about as efficiently as Na ϩ transits a maxi-K ϩ channel; it falls into the category of relatively impermeable. This analysis suggests that the selectivity properties of connexins might exclude the rapid transit of specific solutes such as cAMP and IP 3 . From our studies, it is clear that Cx43 channels will be the most effective in allowing permeation, whereas Cx40 will be least.…”

Section: Channel Permeability Ratiosmentioning

confidence: 99%

“…Three different connexins (Cx43, Cx40, and Cx45) are expressed by cardiac myocytes. [1][2][3] These connexins exhibit different, but overlapping distributions in various regions of the heart. 4 Each of the cardiac connexins forms channels by itself (homomeric/homotypic) that have some differing biophysical properties, including unitary conductances and voltage gating.…”

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confidence: 99%

Cardiac Gap Junction Channels Show Quantitative Differences in Selectivity

Valiūnas

Beyer

Brink

2002

Circulation Research

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136

188

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Abstract-Several proteins including connexin40 (Cx40) and connexin43 (Cx43) form gap junctions between cells of the heart; they may be found separately or may be coexpressed. These connexins form channels with differing conductance and permeability properties. Cx40 and Cx43 are each required for normal electrical conduction between cells in different regions of the heart. We hypothesized that the major difference between these connexins might be in their selective intercellular passage of small molecules such as second messengers, which can be assessed using biologically inert fluorescent probes. Therefore, we designed experimental paradigms to quantitate the permeability properties of these cardiac connexins using simultaneous measurement of junctional conductance (g j ) by the double whole-cell patch-clamp technique and intercellular transfer of Lucifer Yellow (LY) by fluorescence microscopy. These studies were performed in HeLa cells stably transfected with Cx40 or Cx43 or cotransfected with both connexins. We found that homotypic Cx43 channels were about 5 times more permeable to LY than homotypic Cx40 channels (flux of Ϸ1560 versus Ϸ300 molecules/channel per second). Channels between heterotypic (Cx40-Cx43) cell pairs and between pairs of coexpressing cells exhibited intermediate LY permeability. The permeability ratio for LY relative to monovalent cation (K ϩ ) ranged from 0.0025 for Cx40 to 0.028 for Cx43. These permeability ratios suggest that the connexins are highly selective for solutes in the size and charge range of many second messengers. Moreover, the data indicate that coexpression of connexins does not generate unique permeability characteristics, but rather results in an intermediate permeability for

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“…This suggests the presence of different conductance states (main state, residual state, substates) and channel types (homotypic Cx43, heteromeric/ heterotypic Cx43/Cx45) and confirms that gap junction channels in Cx43 ϩ/ϩ ventricular myocytes can be heterotypic and heteromeric. 10 We measured propagation in strands of Cx43 Ϫ/Ϫ ventricular myocytes for the first time. Propagation in Cx43 Ϫ/Ϫ ventricular strands differed significantly from propagation in Cx43 ϩ/ϩ and Cx43 ϩ/Ϫ strands in 2 respects.…”

Section: Beauchamp Et Al Propagation In Cx43-null Myocyte Strandsmentioning

confidence: 99%

Electrical Propagation in Synthetic Ventricular Myocyte Strands From Germline Connexin43 Knockout Mice

Beauchamp

Choby

Desplantez

et al. 2004

Circulation Research

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100

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Abstract-To characterize the role of connexin43 (Cx43) as a determinant of cardiac propagation, we synthesized strands and pairs of ventricular myocytes from germline Cx43 Ϫ/Ϫ mice. The amount of Cx43, Cx45, and Cx40 in gap junctions was analyzed by immunohistochemistry and confocal microscopy. Intercellular electrical conductance, g j , was measured by the dual-voltage clamp technique (DVC), and electrical propagation was assessed by multisite optical mapping of transmembrane potential using a voltage-sensitive dye. Compared with wild-type (Cx43 ϩ/ϩ ) strands, immunoreactive signal for Cx43 was reduced by 46% in Cx43 ϩ/Ϫ strands and was absent in Cx43 Ϫ/Ϫ strands. Cx45 signal was reduced by 46% in Cx43 ϩ/Ϫ strands and to the limit of detection in Cx43 Ϫ/Ϫ strands, but total Cx45 protein levels measured in immunoblots of whole cell homogenates were equivalent in all genotypes. Cx40 was detected in Ϸ 2% of myocytes. Intercellular conductance, g j , was reduced by 32% in Cx43 ϩ/Ϫ cell pairs and by 96% in Cx43 Ϫ/Ϫ cell pairs. The symmetrical dependence of g j on transjunctional voltage and properties of single-channel recordings indicated that Cx45 was the only remaining connexin in Cx43Ϫ/Ϫ cells. Propagation in Cx43 Ϫ/Ϫ strands was very slow (2.1 cm/s versus 52 cm/s in Cx43 ϩ/ϩ ) and highly discontinuous, with simultaneous excitation within and long conduction delays (2 to 3 ms) between individual cells. Propagation was abolished by 1 mmol/L heptanol, indicating residual junctional coupling. In summary, knockout of Cx43 in ventricular myocytes leads to very slow conduction dependent on the presence of Cx45. Electrical field effect transmission does not contribute to propagation in synthetic strands. Key Words: Cx43 Ⅲ Cx45 Ⅲ very slow electrical propagation Ⅲ discontinuous propagation Ⅲ heptanol C onnexin (Cx) proteins form intercellular channels enabling the intercellular exchange of ions and small molecules. 1 In the heart, they facilitate rapid, coordinated electrical excitation, a prerequisite for normal rhythmic contraction. Three different connexins, Cx43, Cx40, and Cx45, are expressed in heart. 2,3 Cx43, the most abundant connexin, is found in ventricular and atrial myocardium. Cx40 is expressed in atrial tissue and the cardiac conduction system. Although Cx45 expression in working ventricular myocardium is modest compared with Cx43, Cx45 is vital for early embryogenesis and cardiac development. 4,5 Cx45 is also expressed in the sinoatrial and atrioventricular nodes. It colocalizes with Cx40 in the conduction system, 6 and with Cx43 in ventricular myocardium. 7 The three cardiac connexins form channels with unique properties. 8 Although multiple connexins are coexpressed in cardiac tissues, their interactions and contributions to electrical or metabolic function are not understood completely. Cx43 and Cx45 likely form heteromeric/heterotypic channels, 9 -12 which may fulfill distinct functions. Cardiac diseases that lead to arrhythmias are associated with gap junction remodeling. [13][14][15] Therefore, know...

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Expression and regulation of connexins in cultured ventricular myocytes isolated from adult rat hearts

Cited by 28 publications

References 39 publications

Neonatal Rat Cardiomyocytes Show Characteristics of Nonhomotypic Gap Junction Channels

Neonatal Rat Cardiomyocytes Show Characteristics of Nonhomotypic Gap Junction Channels

Cardiac Gap Junction Channels Show Quantitative Differences in Selectivity

Electrical Propagation in Synthetic Ventricular Myocyte Strands From Germline Connexin43 Knockout Mice

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