Electrical properties of the gap junctional membrane studied in rat liver cell pairs

Reverdin, E. C.; Weingart, Robert

doi:10.1152/ajpcell.1988.254.2.c226

Cited by 23 publications

(7 citation statements)

References 21 publications

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“…Previous studies on hepatocyte pairs, which express connexin32, failed to detect a major voltage sensitive component of junctional conductance (Spray et al, 1986;Riverdin and Weingart, 1988). The transfected cells used in the present study are more appropriate for dual whole-cell voltage clamp study due to their relatively lower junctional and nonjunctional conductances.…”

Section: Resultsmentioning

confidence: 65%

“…Previous studies on cells dissociated from rat liver, where connexin32 is the dominant gap junction protein, found the junctional membrane to be insensitive to large apparent transjunctional voltages (Spray et al, 1986;Riverdin and Weingart, 1988). However, in a study on liver membranes incorporated into planar lipid bilayers, a small voltage-dependent component was detected (Young et al, 1987).…”

Section: Introductionmentioning

confidence: 89%

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Connexin32 gap junction channels in stably transfected cells. Equilibrium and kinetic properties

Moreno¹,

Eghbali²,

Spray³

1991

Biophysical Journal

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Communication-deficient cells (the SKHep1 cell line) were stably transfected with a plasmid containing cDNA which encodes the major gap junction protein of rat liver, connexin32. Application of the dual whole-cell voltage clamp technique with patch electrodes to pairs of transfected SKHep1 cells revealed strong sensitivity of junctional conductance (gj) to transjunctional voltages (Vjs) of either polarity, with the ratio of minimal to maximal gj (gmin/gmax) being approximately 0.1 at the highest Vjs. Steady-state gj values as a function of voltages of either polarity were well fit by the Boltzmann equation. V0, the voltage at which gj was reduced by 50%, was approximately 25-30 mV; A, the Boltzmann parameter describing voltage dependence, was approximately 0.06 (corresponding to an energy difference between states of approximately 1 kCal/mol and to approximately 2 gating charges moving through the field). The kinetics of the transjunctional voltage dependence were slow (tau greater than 5 s at 20-40 mV, tau = 2 s at and beyond 70 mV). Voltage sensitivity of the opening rate constant (alpha) was approximately 30% lower than that of the closing rate constant (beta) over the Vj range 0-70 mV; at higher voltages, voltage sensitivity of alpha and beta saturated. The kinetic response of gj to a paradigm in which gj was first rendered low by a prepulse of opposite polarity indicated that the voltage sensors are likely to be arranged in series. Transitions between open and closed states in response to transjunctional voltages of either polarity are single order processes; transitions from one closed state to the other involve passage through the open state.

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Section: Resultsmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 89%

Connexin32 gap junction channels in stably transfected cells. Equilibrium and kinetic properties

Moreno¹,

Eghbali²,

Spray³

1991

Biophysical Journal

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“…Not surprisingly, electrophysiological studies on hepatocytes have generated controversial results (see e.g. [13,20,24]). …”

Section: Introductionmentioning

confidence: 99%

Electrophysiological properties of gap junction channels in hepatocytes isolated from connexin32-deficient and wild-type mice

Valiūnas¹,

Niessen

Willecke

et al. 1999

Pfl�gers Archiv European Journal of Physiology

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Hepatocytes were isolated from wild-type and connexin32-deficient (Cx32-deficient) mice. Pairs of cells were chosen to study the electrical properties of gap junction channels using the dual voltage-clamp method. The total gap junction currents revealed that Cx32-deficient hepatocytes express one type of connexin (Cx26) and wild-type hepatocytes express two types of connexins (Cx26 and Cx32). The unitary gap junction currents suggest that Cx32-deficient cells have homotypic channels (Cx26-Cx26) while wild-type cells form homotypic (Cx26-Cx26, Cx32-Cx32) and heterotypic channels (Cx26-Cx32). Homotypic channels exhibited a main conductance and a residual conductance, both virtually insensitive to gap junction voltage (Vj) (Cx32-Cx32: gammaj,main=31 pS, gammaj,residual=9 pS; Cx26-Cx26: gammaj,main=102 pS, gammaj,residual=17 pS). Residual states were regularly seen in Cx32-Cx32 channels, but rarely in Cx26-Cx26 channels. Heterotypic channels showed a main conductance and a residual conductance. The former was sensitive to Vj (average gammaj,main=52 pS). The electrophysiological data suggest that Cx32 hemichannels are more abundant than Cx26 hemichannels in prenatal (ratio 4:1) and adult wild-type hepatocytes (ratio 23:1) and that the total number of gap junction channels is larger in prenatal cells than in adult cells. The diversity of the relationship gj, ss/gj,inst=f(Vj) (gj,ss: gap junction conductance at steady state; gj,inst: instantaneous gap junction conductance; Vj: transjunctional voltage) seen in wild-type cells suggests that the ratio Cx26/Cx32 hemichannels is variable among hepatocytes. A comparison of total and unitary conductances implies that Cx26 hemichannels are down-regulated in Cx32-deficient cells and that docking between Cx26 and Cx32 hemichannels occurs randomly. While the gap junction currents are compatible with homotypic and heterotypic channels, the presence of heteromeric channels cannot be excluded.

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“…Micromolar concentrations of [Ca 2 ] i have been demonstrated to decrease gap junction intercellular communication in a variety of tissues including cardiac muscle and liver (Rose and Loewenstein, 1975;Reverdin and Weingart, 1988). Thus it would be important to understand if changes in intracellular Ca 2 metabolism that may occur with exposure to ELF magnetic ®elds would be related to alterations in gap junction intercellular communication.…”

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confidence: 99%

Inhibition of gap junction intercellular communication by extremely low‐frequency electromagnetic fields in osteoblast‐like models is dependent on cell differentiation

Yamaguchi

Huang

et al. 2002

Journal Cellular Physiology

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Electromagnetic fields have been used to augment the healing of fractures because of its ability to increase new bone formation. The mechanism of how electromagnetic fields can promote new bone formation is unknown, although the interaction of electromagnetic fields with components of the plasma membrane of cells has been hypothesized to occur in bone cells. Gap junctions occur among bone forming cells, the osteoblasts, and have been hypothesized to play a role in new bone formation. Thus it was investigated whether extremely low-frequency (ELF) magnetic fields alter gap junction intercellular communication in the pre-osteoblastic model, MC3T3-E1, and the well-differentiated osteoblastic model, ROS 17/2.8. ELF magnetic field exposure systems were designed to be used for an inverted microscope stage and for a tissue culture incubator. Using these systems, it was found that magnetic fields over a frequency range from 30 to 120 Hz and field intensities up to 12.5 G dose dependently decreased gap junction intercellular communication in MC3T3-E1 cells during their proliferative phase of development. The total amount of connexin 43 protein and the distribution of connexin 43 gap junction protein between cytoplasmic and plasma membrane pools were unaltered by treatment with ELF magnetic fields. Cytosolic calcium ([Ca(2+)](i)) which can inhibit gap junction communication, was not altered by magnetic field exposure. Identical exposure conditions did not affect gap junction communication in the ROS 17/2.8 cell line and when MC3T3-E1 cells were more differentiated. Thus ELF magnetic fields may affect only less differentiated or pre-osteoblasts and not fully differentiated osteoblasts. Consequently, electromagnetic fields may aid in the repair of bone by effects exerted only on osteoprogenitor or pre-osteoblasts.

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Electrical properties of the gap junctional membrane studied in rat liver cell pairs

Cited by 23 publications

References 21 publications

Connexin32 gap junction channels in stably transfected cells. Equilibrium and kinetic properties

Connexin32 gap junction channels in stably transfected cells. Equilibrium and kinetic properties

Electrophysiological properties of gap junction channels in hepatocytes isolated from connexin32-deficient and wild-type mice

Inhibition of gap junction intercellular communication by extremely low‐frequency electromagnetic fields in osteoblast‐like models is dependent on cell differentiation

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