Formation of electrical coupling between embryonic Xenopus muscle cells in culture.

Chow, Ida; Poo, Mu‐ming

doi:10.1113/jphysiol.1984.sp015015

Cited by 23 publications

(8 citation statements)

References 31 publications

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“…Formation of gap junctions can be induced by forcing two single cells into physical contact. In the past, this approach has been adapted to Xenopus blastulae (Loewenstein et al, 1978), Xenopus myoballs (Chow and Poo, 1984;Chow and Young, 1987) and rat cardiocytes (Rook et al, 1988). Here, we show that it is also applicable to the insect cell line C6/36.…”

Section: Discussionmentioning

confidence: 65%

“…It consists of pushing two single cells togethr to establish a physical contact between their cell membranes and thereby allow de novo formation of gap junction channels. In othr contexts, this approach has been used before to examine Xaopus blastulae (Loewenstein et aL, 1978), embryonicXewpus muscle cells (Chow and Poo, 1984;Chow and Young, 1987), and neonatal rat heart cells (Rook et al, 1988).…”

Section: Inwrconmentioning

confidence: 99%

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Voltage-dependent gating of single gap junction channels in an insect cell line

Bukauskas

Weingart

1994

Biophysical Journal

102

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De novo formation of cell pairs was used to examine the gating properties of single gap junction channels. Two separate cells of an insect cell line (clone C6/36, derived from the mosquito Aedes albopictus) were pushed against each other to provoke formation of gap junction channels. A dual voltage-clamp method was used to control the voltage gradient between the cells (Vj) and measure the intercellular current (Ij). The first sign of channel activity was apparent 4.7 min after cell contact. Steady-state coupling reached after 30 min revealed a conductance of 8.7 nS. Channel formation involved no leak between the intra- and extracellular space. The first opening of a newly formed channel was slow (25-28 ms). Each preparation passed through a phase with only one operational gap junction channel. This period was exploited to examine the single channel properties. We found that single channels exhibit several conductance states with different conductances gamma j; a fully open state (gamma j(main state)), several substates (gamma j(substates)), a residual state (gamma j(residual)) and a closed state (gamma j(closed)). The gamma j(main state) was 375 pS, and gamma j(residual) ranged from 30 to 90 pS. The transitions between adjacent substates were 1/7-1/4 of gamma j(main state). Vj had no effect on gamma j(main state), but slightly affected gamma j (residual). The lj transitions involving gamma j(closed) were slow (15-60 ms), whereas those not involving gamma j(closed) were fast (< 2 ms). An increase in Vj led to a decrease in open channel probability. Depolarization of the membrane potential (Vm) increased the incidence of slow transitions leading to gamma j(closed). We conclude that insect gap junctions possess two gates, a fast gate controlled by Vj and giving rise to gamma j(substates) and gamma j(residual), and a slow gate sensitive to Vm and able to close the channel completely.

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Section: Discussionmentioning

confidence: 65%

Section: Inwrconmentioning

confidence: 99%

Voltage-dependent gating of single gap junction channels in an insect cell line

Bukauskas

Weingart

1994

Biophysical Journal

102

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“…Even after the drug treatment, the hyperpolarizations produced by curarization were, in general, small-in the range of 40 PV to 1.5 mV. The cultured Xenopus embryonic muscle cells used in the present study have a high input resistance (Anderson et al, 1979;Chow and Poo, 1984), and their surface AChE has not yet achieved a high activity (Weldon et al, 1981). Both of these factors may account for the high amplitude of curare-induced hyperpolarization.…”

Section: Discussionmentioning

confidence: 80%

“…The average peak amplitude and frequency of these MEPPs were 2.2 + 0.3 mV and 1.3 + 0.5 (n = 7 cells; +SEM), values close to those previously reported in similar Xenopus culture systems (Kidokoro et al, 1980). These MEPPs are much larger than that of the mature neuromuscular junction, presumbly due to the fact that these muscle cells have relatively high input resistance (50 to 100 megohms; Chow and Poo, 1984; see also Anderson et al, 1979).…”

Section: Resultsmentioning

confidence: 99%

Non-quantal release of acetylcholine at a developing neuromuscular synapse in culture

Sun¹,

Poo²

1985

J. Neurosci.

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Local, pulsed application of d-tubocurarine at neuromuscular synapses in embryonic Xenopus nerve-muscle culture resulted in a transient hyperpolarization of muscle membrane potential. Miniature endplate potentials (MEPPs) were abolished during the hyperpolarization and recovered after the return of resting membrane potential. The magnitude of hyperpolarization was independent of the frequency of MEPPs before curarization, and it had an average peak value of 4.3 mV in medium containing physiological levels of Ca*+. Prolonged application of curare or a-bungarotoxin led to sustained hyperpolarizations up to 8 mV in magnitude. Denervation produced by mechanically removing the neurite from the muscle cell also produced similar hyperpolarization, and curarization after denervation was without significant hyperpolarizing effect. Increasing the extracellular Ca*+ concentration to about 8 mM abolished the curare-induced hyperpolariration response, in sharp contrast to its effect in elevating the frequency of MEPPs. Taken together, our results indicate that innervated embryonic muscle cells were maintained at a depolarized state relative to that of uninnervated muscle cells by a steady, spontaneous release of acetylcholine (ACh) from the innervating neurite. The cellular mechanism underlying this mode of ACh release appears to be different from that of the quanta1 ACh release responsible for MEPPs.The nerve impulse is transmitted across the neuromuscular junction through the triggering of a simultaneous release from the nerve terminal of many packages, or "quanta," of acetylcholine (ACh) molecules, which open the ionic channels in the postsynaptic muscle membrane and induce depolarization and excitation of the muscle cell (del Castillo and Katz, 1954). In the absence of a nerve impulse, quanta1 release of ACh occurs randomly at a low frequency, as indicated by the appearance of small muscle membrane depolarizations, or miniature endplate potentials (MEPPs), that can be detected at the muscle cell near the synaptic junction (Fatt and Katz, 1952). Previous biochemical and physiological evidence suggests that a substantial amount of ACh is also released from the nerve by a mechanism independent of nerve impulse activity or the MEPPs

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“…The developmental significance of this early ACh secretion is now beginning to be understood. Because of the high input resistance of the embryonic muscle cell (Chow and Poo, 1984) spontaneous ACh secretion at developing synapses produces large postsynaptic potentials, many of which are capable of inducing action potentials and contraction of the muscle cell (Xie and Poo, 1986). It has been shown that the differentiation of muscle striations in Xenopus myocytes is regulated by the ACh-induced contraction during the first few days of synaptogenesis (Kidokoro and Saito, 1988).…”

Section: Discussionmentioning

confidence: 99%

Depression of developing neuromuscular synapses induced by repetitive postsynaptic depolarizations

Lin

Sanes

et al. 1994

J. Neurosci.

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Effect of postsynaptic activity on the synaptic efficacy was studied in Xenopus nerve-muscle cultures. Repetitive postsynaptic depolarizations induced by injection of current pulses into singly innervated myocytes resulted in significant reduction in the frequency of spontaneous synaptic currents and the amplitude of nerve-evoked synaptic currents at the majority of synapses that showed immature synaptic properties. Repetitive hyperpolarizations and steady depolarizations of similar duration were without effect. The depolarization-induced synaptic depression appeared to result predominantly from a reduced ACh secretion from the presynaptic nerve terminal. Buffering the myocyte cytosolic Ca2+ at a low level with intracellular loading of a Ca2+ buffer, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA), significantly reduced the effect of the depolarizations. Thus postsynaptic electrical activity can regulate the synaptic efficacy of the developing neuromuscular synapases and the regulation may be mediated by retrograde transsynaptic interactions.

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Formation of electrical coupling between embryonic Xenopus muscle cells in culture.

Cited by 23 publications

References 31 publications

Voltage-dependent gating of single gap junction channels in an insect cell line

Voltage-dependent gating of single gap junction channels in an insect cell line

Non-quantal release of acetylcholine at a developing neuromuscular synapse in culture

Depression of developing neuromuscular synapses induced by repetitive postsynaptic depolarizations

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