Voltage independence of an electrotonic synapse

Johnston, Michelle; Ramón, Fidel

doi:10.1016/s0006-3495(82)84497-4

Cited by 21 publications

(10 citation statements)

References 14 publications

(2 reference statements)

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“…4B), whereas, at higher transjunctional potentials, the conductance of Px1͞Px2 channels displayed only a very modest reduction (Ϸ15%) of the initial values (Fig. 4C), which was similar to what was reported for crayfish septate junctions (34) and human Cx31.9 (32). Although it has been reported that junctional currents measured in insect cells are sensitive to changes in membrane potential (35), the relative voltage insensitivity of pannexin intercellular channels with polarization of one cell is a strong indication that polarization of both cells is not likely to affect significantly junctional conductance.…”

Section: Functional Expression In Paired Xenopussupporting

confidence: 87%

Pannexins, a family of gap junction proteins expressed in brain

Bruzzone

Hormuzdi

Barbe

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

708

826

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Database search has led to the identification of a family of proteins, the pannexins, which share some structural features with the gap junction forming proteins of invertebrates and vertebrates. The function of these proteins has remained unclear so far. To test the possibility that pannexins underlie electrical communication in the brain, we have investigated their tissue distribution and functional properties. Here, we show that two of these genes, pannexin 1 (Px1) and Px2, are abundantly expressed in the CNS. In many neuronal cell populations, including hippocampus, olfactory bulb, cortex and cerebellum, there is coexpression of both pannexins, whereas in other brain regions, e.g., white matter, only Px1-positive cells were found. On expression in Xenopus oocytes, Px1, but not Px2 forms functional hemichannels. Coinjection of both pannexin RNAs results in hemichannels with functional properties that are different from those formed by Px1 only. In paired oocytes, Px1, alone and in combination with Px2, induces the formation of intercellular channels. The functional characteristics of homomeric Px1 versus heteromeric Px1͞Px2 channels and the different expression patterns of Px1 and Px2 in the brain indicate that pannexins form cell type-specific gap junctions with distinct properties that may subserve different functions.

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Section: Functional Expression In Paired Xenopussupporting

confidence: 87%

Pannexins, a family of gap junction proteins expressed in brain

Bruzzone

Hormuzdi

Barbe

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

708

826

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“…Rather, we favour the notion that this rarely observed slowly developing current reflects variations in the junctional current itself due to uncontrolled environmental factors such as temperature (Harris, Spray & Bennett, 1980;Jaslove & Brink, 1986) which may affect the gap junction permeability (Spray, White, Campos de Carvalho, Harris & Bennett, 1984) and/or kinetics. (Auerbach & Bennett, 1969) Yes Comparison with other voltage-controlled gap junctions Junctional channels controlled by potential are present mainly during embryonic stages while in adult tissues, voltage dependence of gap junctions is uncommon (Johnston & Ramon, 1982;Verselis & Brink, 1984;White, Spray, Schwartz, Wittenberg & Bennett, 1984;Spray, Ginzberg, Morales, Bennett, Babayastky, Gatmaitin & Arias, 1984;Bodmer & Spray, 1985;Weingart, 1986) and so far has been found to occur only between neurones. The voltage-dependent properties of the gap junctions studied to date are summarized in Table 2, which shows that channels at the crayfish rectifying synapse share some characteristics with those of amphibian embryonic cells.…”

Section: Discussionmentioning

confidence: 99%

Voltage‐clamp analysis of a crayfish rectifying synapse.

Giaume

Kado

Korn

1987

The Journal of Physiology

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SUMMARY1. The rectifying crayfish giant motor synapse has been studied in the second abdominal ganglion, using the double-voltage-clamp technique which allowed direct measurements of junctional current at various fixed transjunctional potentials.2. The transjunctional potential (Vj), defined as the difference between the voltages recorded in the lateral giant axon and the giant motor fibre, was varied from -70 to +50 mV, the minimum and maximum junctional chord conductances (gmin and gmax' respectively) were found to be 1-2 + 1-3 ,uS (n = 10) and 22-9 ± 6-3 ,uS (n = 10), respectively.3. For a given Vi, changes in the lateral giant axon or giant motor fibre membrane potential over a range of + 30 mV around their resting levels did not influence the junctional permeability (gj), indicating that the inside-outside potential of the junctional channel does not control gj.4. Therefore, the steady-state junctional chord conductances were dependent only upon Vi.5. The voltage dependence of the chord conductance was well fitted by a modified Boltzmann relation given by the equationwith the constants: A = 0 15+0-03 mV-1 (n = 10) and VI = 28±4 mV (n = 10); the latter two parameters were also found to be independent of both transmembrane potentials.6. The junctional currents were already constant 1 ms after step changes in the junctional voltage; this was three orders of magnitude faster than the other known examples of voltage-controlled gap junctions between embryonic cells. 7. Our results may be interpreted by a highly voltage-dependent probability of opening of the junctional channels. They also suggest that the gap-junction channels forming the giant motor synapse respond very rapidly to potential and that the hemi-channels which constitute them may not be symmetric.

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“…Gap junctions between rat neonatal cardiac myocytes (Rook et al, 1988), rat hepatocytes (Spray et al, 1990) and Xenopus oocytes expressed from connexin 32 or 26 cRNA (Barrio et al, 1990) were more recently reported to display voltage dependence of the transjunctional type. Gap junctions in many other preparations have little if any voltage dependence, including crayfish (Johnston and Ramon, 1982) and earthworm septate axons (Verselis and Brink,…”

Section: Introductionmentioning

confidence: 99%

A voltage-dependent gap junction in Drosophila melanogaster

Verselis

Bennett

Bargiello

1991

Biophysical Journal

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Steady-state and kinetic analyses of gap junctional conductance, gi, in salivary glands of Drosophila melanogaster third instar larvae reveal a strong and complex voltage dependence that can be elicited by two types of voltages. Voltages applied between the cells, i.e., transjunctional voltages, Vj, and those applied between the cytoplasm and the extracellular space, inside-outside voltages, Vi,o, markedly alter gj. Alteration of Vi-o while holding Vj = O,i.e., by equal displacement of the voltages in the cells, causes gj to increase to a maximum on hyperpolarization and to decrease to near zero on depolarization. These conductance changes associated with Vi-o are fit by a model in which there are two independent gates in series, one in each series, one in each membrane, where each gate is equally sensitive to Vi-o and exhibits first order kinetics. Vj's generated by applying voltage steps of either polarity to either cell, substantially reduce gj. These conductance changes exhibit complex kinetics that depend on Vi-o as well as Vj. At more positive Vi-o's, the changes in gj have two phases, an early phase consisting of of a decrease in gj for either polarity of Vj and a later phase consisting of an increase in gj on hyperpolarizing either cell and a decrease on depolarizing either cell. At negative Vi-o's in the plateau region of the gj-Vi-o relation, the later slow increase in gj is absent on hyperpolarizing either cell. Also, the early decrease in gj for either polarity of Vj is faster the more positive the Vi-o. The complex time course elicited by applying voltage steps to one cell can be explained as combined actions of Vi-o and Vj, with the early phase ascribable to Vj, but influenced by Vi-o, and the later phase to the changes in Vi-o associated with the generation of Vj. The substantially different kinetics and sensitivity of changes in gj by Vi-o and Vj suggests that the mechanisms of gating by these two voltages are different. Evidently, these gap-junction channels are capable of two distinct, but interactive forms of voltage dependence.

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Voltage independence of an electrotonic synapse

Cited by 21 publications

References 14 publications

Pannexins, a family of gap junction proteins expressed in brain

Pannexins, a family of gap junction proteins expressed in brain

Voltage‐clamp analysis of a crayfish rectifying synapse.

A voltage-dependent gap junction in Drosophila melanogaster

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