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

Kullberg, R; Owens, Jesse

doi:10.1113/jphysiol.1986.sp016088

Cited by 17 publications

(10 citation statements)

References 30 publications

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“…The recent discovery (Mishina et al, 1986) of a separate gene transcript encoding an adult form of the y-subunit of bovine AChR leaves little doubt that the 2 classes of AChR represent separate molecules, rather than different functional states of a single receptor type. Although the precise physiological significance for the existence of 2 types of AChRs is unknown, it is well-documented that the distribution and functional states of these 2 types of channels are not fixed but are labile and are altered during certain processes such as embryonic development (Fischbach and Schuetze, 1980;Michler and Sakmann, 1980;Brehm et al, 1984;Leonard et al, 1984;Siegelbaum et al, 1984) metamorphosis (Kullberg and Owens, 1986) innervation (Brenner and Sakmann, 1983), denervation (Allen and Albuquerque, 1986), or desensitization (Auerbach and Lingle, 1986;Igusa and Kidokoro, 1987).…”

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confidence: 99%

Early development of two types of nicotinic acetylcholine receptors

Leonard

Nakajima

et al. 1988

J. Neurosci.

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Functional changes of acetylcholine receptor (AChR) channels in embryonic Xenopus myotomal muscle cells were examined during their development in culture. Single-channel currents evoked by 50 or 500 nM ACh were measured using the patch-clamp technique. In Xenopus myocytes the first emergence of AChRs takes place at about stage 20 (Nieuwkoop and Faber). Myotomes were dissociated at very early stages and plated in culture. Single-channel currents through AChRs were recorded at times ranging from a few hours (stage 21) to several days (stage 47) after the first emergence of AChRs. Two classes of AChR channel were recorded: One class had a low conductance with a long burst duration (low-conductance channel), and the other had a high conductance with a short burst duration (high-conductance channel). Both of these classes were active from the earliest time recorded (stages 21-24). One effect of development was a shift in the relative activity of the low- and high-conductance channels. Initially (stages 21-24), the low conductance channels predominated, accounting for over 95% of the observed events. After 3 d in culture, however, high- and low-conductance events occurred with roughly equal frequency. The other effect of development was a 4-fold decrease in the mean burst length of the low-conductance channel. The decrease in burst length took place rapidly, with about 60% of the change occurring within 24 hr in culture. The burst length of the high-conductance channel remained virtually constant during development, as did the unitary conductance of both channels and the voltage dependence of their mean burst lengths. The developmental change in the proportion of low- and high-conductance channels is likely due to the increased insertion of new high-conductance channels. However, the molecular mechanism of the shortening of burst length of the low-conductance channel is unknown.

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confidence: 99%

Early development of two types of nicotinic acetylcholine receptors

Leonard

Nakajima

et al. 1988

J. Neurosci.

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“…We interpret these results to mean that androgen-dependent activational changes in proteins mediating contraction are sufficient to generate the appropriate muscle mechanics needed for the clasping behavior and that significant remodeling of the synapse on a seasonal basis may be a costly procedure that would not be evolutionarily advantageous. We find these results to be interesting because previous studies have provided evidence suggesting that fiber contraction and synaptic properties are under coordinate regulation (Miledi and Uchitel, 1981;Fedorov et al, 1982;Kullberg and Owens, 1986;Henderson and Brehm, 1989). Our results suggest that in adult frogs, these two fundamental aspects of muscle function appear to be differentially susceptible to regulation by androgens.…”

Section: Discussionmentioning

confidence: 70%

“…Single fibers of the submaxillaris muscle exhibit both long branched end plates and small boutonlike contacts, which characterize fast twitch and slow tonic fibers, respectively (Miledi and Uchitel,198 1). Functional analysis indicates that intermediate fibers express a class of ACh receptor with open time kinetics lying between those of fast twitch and slow tonic fibers leading to the generation of synaptic currents of intermediate duration (Miledi and Uchitel, 1981;Fedorov et al, 1982;Kullberg and Owens, 1986). Prolongation of synaptic currents by cholinesterase inhibitors suggests that AChE activity in intermediate fibers is higher than in slow tonic and lower than in fast twitch fibers (Fedorov et al, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…Prolongation of synaptic currents by cholinesterase inhibitors suggests that AChE activity in intermediate fibers is higher than in slow tonic and lower than in fast twitch fibers (Fedorov et al, 1982). Finally, it has been shown for the intermediate fibers of the interhyoideus muscle in Xenopus, that synaptic currents undergo developmental changes in kinetics that correlate directly with developmental changes in the kinetics of contraction (Kullberg and Owens, 1986). Taken together, these data suggest that muscle fibers may coordinately regulate expression of components of the synaptic apparatus with expression of contractile proteins.…”

Section: Introductionmentioning

confidence: 99%

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Androgen regulation of neuromuscular junction structure and function in a sexually dimorphic muscle of the frog Xenopus laevis

Brennan

Henderson

1995

J. Neurobiol.

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Specific forelimb muscles in anurans are sexually dimorphic and underlie the androgen-dependent clasping response of males during amplexus. Previous studies have reported that androgen treatment slows the contractile properties of these sexually dimorphic forelimb muscles. In amphibians, the expression of functionally distinct acetylcholine (ACh) receptors, the levels of acetylcholinesterase (AChE), the extent of multiple innervation, and the structure of individual end plates vary with the contractile properties of the muscle fibers. In higher vertebrates, androgens have been reported to alter the expression of ACh receptors, AChE, and the neuromodulator, calcitonin gene-related peptide (CGRP). To determine whether the known androgen-dependent changes in contraction of androgen-sensitive forelimb muscles are accompanied by concomitant changes in synaptic structure or function, we have compared functional neuromuscular transmission, the pattern of innervation, and CGRP immunoreactivity in nerve or muscle preparations from castrated (C) and castrated and testosterone-treated (CT) adult male Xenopus laevis. CGRP expression in androgen receptor (AR)-immunopositive neurons was increased in CT animals. However, no significant differences were found in ACh-mediated single channel or macroscopic currents, the extent of multiple end plates, or end plate morphology for forelimb fibers isolated from C and CT Xenopus. In contrast, analysis of forelimb fibers from gonadally intact adult females and juvenile animals of both sexes revealed that macroscopic synaptic currents were significantly shorter in these animals than in either C or CT adult males. Our data suggest that forelimb fibers in sexually dimorphic muscles of Xenopus do show significant differences in synaptic transmission; however, neither end-plate organization nor functional neuromuscular transmission are subject to activational effects of androgens in adult male frogs.

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“…The interhyoideus, a flat muscle of the lower jaw, begins to develop at about the same time. In other studies, we have shown that these muscles differ in their development of endplate currents and probably have 3 distinct patterns of AChR development (Kullberg et al, 1985;Kullberg and Owens, 1986).…”

Section: Methodsmentioning

confidence: 99%

Three conductance classes of nicotinic acetylcholine receptors are expressed in developing amphibian skeletal muscle

Owens

Kullberg

1989

J. Neurosci.

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Two previously described classes of nicotinic AChRs in vertebrate skeletal muscle have conductances of 40 and 60 pS. In addition, a third conductance class of AChR channels is present in developing Xenopus muscle. This class appears to represent an independent channel type, rather than a subconductance state of the larger conductance channels. The channel has a slope conductance of 25 pS and a reversal potential of about 0 mV membrane potential. Its kinetic properties resemble those of the 40 pS channels present in early embryonic myotomal muscle. The channel has a mean open time of about 6 msec (at 40 mV applied potential). The open time is dependent on membrane potential and increases e-fold for every 60 mV of hyperpolarization. Consecutive openings were often separated by brief closures of about 0.4 msec in duration. The identity of the channel as a nicotinic AChR was established by blocking the channel openings with alpha-BTX and by demonstrating bursting and desensitization in the presence of high agonist concentrations. In some muscles (e.g., extraocular), this channel may be a predominant form at early developmental stages and could therefore be important to the function of developing synapses in those muscles.

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

Cited by 17 publications

References 30 publications

Early development of two types of nicotinic acetylcholine receptors

Early development of two types of nicotinic acetylcholine receptors

Androgen regulation of neuromuscular junction structure and function in a sexually dimorphic muscle of the frog Xenopus laevis

Three conductance classes of nicotinic acetylcholine receptors are expressed in developing amphibian skeletal muscle

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