Electrotonic coupling in internally perfused crayfish segmented axons.

Gap junctions are connexin-formed channels that play an important role in intercellular communication in most cell types. In the immune system, specifically in macrophages, the expression of connexins and the establishment of functional gap junctions are still controversial issues. Macrophages express P2X7 receptors that, once activated by the binding of extracellular ATP, lead to the opening of transmembrane pores permeable to molecules of up to 900 Da. There is evidence suggesting an interplay between gap junctions and P2 receptors in different cell systems. Thus, we used ATP-sensitive and -insensitive J774.G8 macrophage cell lines to investigate this interplay. To study junctional communication in J774-macrophage-like cells, we assessed cell-to-cell communication by microinjecting Lucifer Yellow. Confluent cultures of ATP-sensitive J774 cells (ATP-s cells) are coupled, whereas ATP-insensitive J774 cells (ATP-i cells), derived by overexposing J774 cells to extracellular ATP until they do not display the phenomenon of ATP-induced permeabilization, are essentially uncoupled. Western-blot and reverse-transcription polymerase chain reaction assays revealed that ATP-s and ATP-i cells express connexin43 (Cx43), whereas only ATP-s cells express the P2X7 receptor. Accordingly, ATP-i cells did not display any detectable ATP-induced current under whole-cell patch-clamp recordings. Using immunofluorescence microscopy, Cx43 reactivity was found at the cell surface and in regions of cell-cell contact of ATP-s cells, whereas, in ATP-i cells, Cx43 immunoreactivity was only present in cytosolic compartments. Using confocal microscopy, it is shown here that, in ATP-s cells as well as in peritoneal macrophages, Cx43 and P2X7 receptors are co-localized to the membrane of ATP-s cells and peritoneal macrophages.

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“…2D). Octanol, a known gap-junction inhibitor (Johnston and Ramon, 1981), significantly reduced dye coupling in ATP-s cells (Fig. 3).…”

Section: Dye Couplingmentioning

confidence: 88%

Modulation of intercellular communication in macrophages: possible interactions between GAP junctions and P2 receptors

Fortes

Pecora

Persechini

et al. 2004

Journal of Cell Science

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“…C a 2ϩ might not always interact directly with gap junctions but rather via a cytoplasmic intermediate. The sensitivity to C a 2ϩ disappeared after internal perf usion of, for example, crayfish segmented axons but recovered when calmodulin was added (Johnston and Ramon, 1981;Arellano et al, 1988). Conditions favoring phosphorylation of the channel protein also increased the sensitivity to calcium in the same preparation (Arellano et al, 1990).…”

Section: Calcium and Hydrogen Ions As Modulators Of Gap Junctional Pementioning

confidence: 98%

Astrocytic Gap Junctions Remain Open during Ischemic Conditions

et al. 1998

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Gap junctions are highly conductive channels that allow the direct transfer of intracellular messengers such as Ca 2ϩ and inositol triphosphate (IP 3 ) between interconnected cells. In brain, astrocytes are coupled extensively by gap junctions. We found here that gap junctions among astrocytes in acutely prepared brain slices as well as in culture remained open during ischemic conditions. Uncoupling first occurred after the terminal loss of plasma membrane integrity. Gap junctions therefore may link ischemic astrocytes in an evolving infarct with the surroundings. The free exchange of intracellular messengers between dying and potentially viable astrocytes might contribute to secondary expansion of ischemic lesions.

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“…Johnston and Ramon (1981) Peracchia et al (1981) suggested that the cytoplasmic intermediate is calmodulin, since a calmodulin inhibitor prevents gap junction crystallization and electrical uncoupling. Calmodulin is a known enzyme activator, so changes in the configuration of the tubules of the junctional membrane also may involve an enzyme located along the nexus.…”

Section: Implications For Intracellular Eventsmentioning

confidence: 99%

Active modulation of electrical coupling between cardiac cells of the dog. A mechanism for transient and steady state variations in conduction velocity.

Spach¹,

Kootsey²,

Sloan

1982

Circulation Research

108

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SUMMARY. Propagation velocities of action potentials were measured simultaneously along the longitudinal and transverse axes of cardiac fibers in ventricular muscle. The anisotropic distribution of propagation velocities was found to be altered transiently and in the steady state by the rate and pattern of stimulation and by ouabain. The relative amount of velocity change varied with the direction of propagation and was greatest in the direction perpendicular to the long fiber axis. None of the variables usually associated with the membrane ionic mechanism of depolarization-resting potential, V max , and Tfoot-showed enough variation to account for the observed changes in velocity.A simplified anisotropic propagation model representing the internal current pathway as an alternating sequence of cytoplasmic and junctional resistance is presented, taking into account the larger contribution to the internal resistance made by the cell couplings in the transverse direction than in the longitudinal direction. On the basis of this model, it was concluded that the observed changes in velocity were due to changes in cell coupling. Both transient and steady state velocity changes were found to correspond to changes in the action potential duration, suggesting that there is a common factor, such as the internal calcium and/or sodium concentrations, linking the control of the action potential duration and the coupling resistance between cardiac cells.

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Electrotonic coupling in internally perfused crayfish segmented axons.

Cited by 69 publications

References 15 publications

Modulation of intercellular communication in macrophages: possible interactions between GAP junctions and P2 receptors

Modulation of intercellular communication in macrophages: possible interactions between GAP junctions and P2 receptors

Astrocytic Gap Junctions Remain Open during Ischemic Conditions

Active modulation of electrical coupling between cardiac cells of the dog. A mechanism for transient and steady state variations in conduction velocity.

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