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  • 1
    ISSN: 1432-1424
    Keywords: beat-rate synchronization ; morphometry ; junctional conductance ; voltage clamp ; single-channel conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The time course of gap junction formation and growth, following contraction synchronization of cardiac myocytes in culture, has been studied in a combined (electro)physiological and ultrastructural study. In cultures of collagenase-dissociated neonatal rat cardiocytes, pairs of spontaneously beating myocytes synchronized their contractions within one beat interval within 2–20 min after they apparently had grown into contact, 45 sec after the first synchronized beat an appreciable junctional region containing several small gap junctions was already present. In the following 30 min, neither the area of individual gap junctions nor their total area increased, 75 min after synchronization both the area of individual gap junctions and their total area had increased by a factor of 10–15 with respect to what was found in the first half hour. In the period between 75 and 300 min again no further increase in gap junctional area was found. In double voltage-clamp experiments, gap junctions between well-coupled cells behaved like ohmic conductors. In poorly coupled cells, in which the number of functional gap-junctional channels was greatly reduced, the remaining channels showed voltage-dependent gating. Their single-channel conductance was 40–50 pS. The electrophysiologically measured junctional conductance agreed well with the conductance calculated from the morphometrically determined gap-junctional area. It is concluded that a rapid initial gap junction formation occurs during the 2–20 min period prior to synchronization by assembly of functional channels from existing channel precursors already present in the cell membranes. It then takes at least another 30 min before the gap-junctional area increases possibly byde novo synthesis or by recruitment from intracellular stores or from nonjunctional membranes, a process completed in the next 45 min.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 348 (1994), S. 97-104 
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 414 (1989), S. 95-98 
    ISSN: 1432-2013
    Keywords: cardiac fibroblasts and myocytes ; voltage clamp ; gating ; gap junction channel conductance ; connexons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Recently, the use of the double whole-cell patchclamp technique enable conductance measurements of single gap junctional channels. Different values have been measured in pairs of rat lacrimal cells (6), murine acinar cells and chinese hamster ovary cells (9), embryonic chick heart- (10) and neonatal rat heart myocytes (7). We here present evidence that the conductance of gap junction channels between two different cell types originating from the same tissue, neonatal rat heart, is different. In mixed cultures of cardiac fibroblasts and myocytes, gap junction channels between fibroblasts have a single channel conductance of only 22 pS, while those between myocytes have a conductance of 43 pS. Fibroblasts can be electrically coupled to myocytes through channels having an intermediate conductance of 29 pS, a value which matches very well with te theoretically expected conductance of a gap junction channel composed of a fibroblast- and a myoblast connexon (hemichannel). These data provide direct evidence on the single channel level that in heterologous gap junction channels the composing connexons retain their cell-specific properties.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 431 (1995), S. 138-140 
    ISSN: 1432-2013
    Keywords: Connexins ; Voltage-clamp ; Intracellular pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Intercellular communication through gap junction channels can be regulated by changes in intracellular pH (pHi). This regulation may play an important role in ischemic heart tissue. Using the dual voltage-clamp technique, we compared the pHi sensitivity of gap junction channels composed of connexin 43 (Cx43) and Cx45, two of the gap junction proteins that are expressed in heart. We made use of SKHep1 cells, endogenously expressing low levels of Cx45 and SKHep1 cells stably transfected with rat Cx43. To manipulate the pHi we applied the NH3/NH4 + pH-clamp method. At pHi 6.7 the gj of Cx45 channels was reduced to ∼20% of control values (pHi 7.0) and at pHi 6.3 all channels closed. The gj of Cx43 channels was ∼70% of control values at pHi 6.7 and ∼40% at pHi 6.3. Cx43 channels closed at pHi 5.8. Single channel conductances were 17.8 pS for Cx45 and 40.8 pS for Cx43 at pHi 7.0 and did not change significantly at lower pHi. This suggests that the decrease in macroscopic conductance observed at low pHi results from the decrease in open probability of gap junctional channels rather than from a decrease in single channel conductance. Our results demonstrate that gap junction channels built of Cx45 are far more pH sensitive than channels built of Cx43.
    Type of Medium: Electronic Resource
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