Acetylcholine receptor channel properties during development of Xenopus muscle cells in culture.

Abstract

SUMMARY1. Developmental changes in acetylcholine (ACh) receptor channel function on aneural cultures of embryonic myotomal muscle cells were examined using the patch-clamp technique.2. At all stages of differentiation two different unitary-event amplitudes were observed, corresponding to high-y (single-channel conductance) (64 pS) and low-y (46 pS) channel types. No change in conductance occurred for either channel type during the 6-day in vitro period examined.3. At resting membrane potential (-85 mV) the low-y channel exhibited a mean open time of approximately 2 ms which, on the average, was 2-3-fold longer than that measured for the high-y channel. Neither the estimated mean channel open time nor the voltage dependence of the open state measured for either channel type changed during development.4. In recordings with low ACh concentration (041-0-25 ,SM) both high-y and low-y channel types exhibited non-stationary opening probabilities over the recording period. Usually the opening rate of both channel types decreased with time following seal formation, however, the 'drop-out' rate was faster for the low-y channel.5. A developmental increase in the proportion of high-y events occurred between day 1 (16 %) and day 5 (56 %) in culture, paralleling the time-dependent changes in the channel kinetics based on ACh-activated membrane noise.6. We conclude that the development of non-junctional muscle membrane is associated with increased expression of high-y channels and that this process is primarily responsible for the previously reported developmental alterations in macroscopic ACh receptor channel currents.

Comparative development of end‐plate currents in two muscles of Xenopus laevis.

“…decays were apparently well fitted by single-exponential curves probably reflects our inability to resolve two components by eye when one component largely outweighs the other. In general, the single-exponential decays fell within the limits of the fast and slow channel open times previously described by spectral analysis of ACh noise and by single channel recordings from myotomal muscle (Brehm, Kullberg & Moody-Corbett, 1984;Brehm, Kidokoro & Moody-Corbett, 1984;Kullberg & Kasprzak, 1985).…”

Direct Measurements of Presynaptic Calcium and Calcium-Activated Potassium Currents Regulating Neurotransmitter Release at CulturedXenopusNerve–Muscle Synapses

“…Within hours of contact, they resemble mature cholinergic synapses in many respects. They exhibit spontaneous release, high quantal content-evoked release, membrane thickenings, clouds of vesicles, and postsynaptic aggregation of ACh receptors (Anderson et al, 1977;Weldon and Cohen, 1979;Cohen and Weldon, 1980;Kidokoro et al, 1980;Kidokoro and Yeh, 1982;Brehm et al, 1984;Takahashi et al, 1987;Buchanan et al, 1989;Evers et al, 1989).…”

Control of end‐plate channel properties by neurotrophic effects and by muscle activity in rat.

“…This is consistent with recent indications that the relative dependence of different junctional properties on muscle activity, trophic influences and intrinsic developmental programmes may vary, both within but especially between different species. Thus, in embryonic amphibian muscle, the frequency of fast channel openings increases with age even when the cultures are raised in the absence of neurones (Brehm et al 1982(Brehm et al , 1984, suggesting that an innervating nerve may simply concentrate preformed adult-type ACh receptors underneath its terminals. In chicken muscle, on the other hand, channel conversion does not occur even at normally innervated end-plates (Schuetze, 1980).…”