Interactions Between Calcium and Barium on the Spontaneous Release of Transmitter From Mammalian Motor Nerve Terminals

Laskowski, Michael B.; Thies, Roger

doi:10.3109/00207457209147159

Cited by 13 publications

(12 citation statements)

References 20 publications

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“…at 2 mm than at 0.5 mm (see also Laskowski & Thies, 1972). Cells were also depolarized following the removal of added Ca2+, but to a lesser extent and spontaneous action potential firing was less common.…”

Section: Effects On Membrane Propertiesmentioning

confidence: 93%

“…A partial agonist might have been expected to produce substantial inhibition of release at high Ca2+ concentrations, but this was never observed. It seems possible that direct transfer from Ca2+ solutions into Ba2+ solutions prevents the displacement of some of the Ca2+ from the tissue, thus maintaining some 'phasic' release; it is unclear whether retention of Ca2+ occurs at an intracellular or an extracellular location (see Baker, 1972;Hubbard, 1973 (Laskowski & Thies, 1972). It appears that, if preganglionic terminals are depolarized by Ba2+, the effect must be small and would seem unlikely to account for the actions of Ba2+ described in this report.…”

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confidence: 99%

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The effects of strontium and barium ions at synapses in sympathetic ganglia.

McLachlan¹

1977

The Journal of Physiology

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Section: Effects On Membrane Propertiesmentioning

confidence: 93%

mentioning

confidence: 99%

The effects of strontium and barium ions at synapses in sympathetic ganglia.

McLachlan¹

1977

The Journal of Physiology

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“…This might suggest that Ba would elicit intense secretion in the whole subclass of secretary cells with such channels (Douglas, 1978). But this is not so for Ba has only rather modest effects on basal secretary activity of nerve terminals (Douglas, Lywood & Straub, 1961;Boullin, 1967;Kirpekar & Misu, 1967;Laskowski & Thies, 1972;Silinsky, 1978). Despite their suggested common neuroectodermal origin with neurones (see Pearse, 1978), these endocrine cells evidently have some property, revealed by their responsiveness to Ba, that distinguishes them from nerve endings.…”

Section: Intracellular Secretagogue Action Of Bamentioning

confidence: 99%

Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.

Douglas¹,

Taraskevich²,

Tomiko³

1983

The Journal of Physiology

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Ba ions caused an intense and prolonged discharge of melanocyte‐stimulating hormone (MSH) from perifused neurointermediate lobes of mouse pituitaries and dispersed pars intermedia cells. The effect persisted in chronically cultured lobes or cells. It did not require Ca, but, like the Ca‐dependent response to excess K, was blocked by cyanide combined with glucose lack. The secretagogue effect of Ba was blocked or prevented by Co or by excess Ca, both of which can reduce inward Ba currents through Ca channels. Prior exposure to excess K partially reduced the secretagogue effect of Ba, suggesting that depolarization caused some inactivation of Ba current. In contrast to Ba, excess K elicited secretion that was transient, and prior exposure of preparations to excess K (in the absence of Ca) profoundly suppressed the secretagogue effect of Ca. The evidence is consistent with the view that inward Ca current rapidly inactivates in these cells. It is concluded that Ba ions have a potent and persistent direct secretagogue effect on the melanotrophs that may reflect, in part, their ability to penetrate Ca channels more easily than Ca ions. The strong secretagogue effects of Ba on melanotrophs may be of considerable utility in studies on MSH secretion since a physiological secretagogue has yet to be discovered. Moreover, since the responses of melanotrophs (and other endocrine cells) to Ba can be distinguished from those of various other secretory cells and neurones, it is suggested that Ba may provide a tool for characterizing the distinctive membrane properties of the Ba‐responsive endocrine cells.

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“…For example, the results of Miledi (1966) and Blioch, Glagoleva, Liberman & Nenashev (1968) with frog motor nerve terminals suggest that end-plate potentials (e.p.ps) are only occasionally detectable in Ba solutions, and when produced involve the release of a very small fraction of the quantal output normally observed in Ca solutions. Several reviewers (Hubbard, 1973;Ginsborg & Jenkinson, 1976) have in fact suggested that these small e.p.ps reflect the transient displacement of membrane Ca by Ba (Laskowski & Thies, 1972) (1-10 gg/ml) and tubocurarine chloride (2.5,g/ml)…”

mentioning

confidence: 99%

“…The responses to supramaximal nerve stimulation were recorded intracellularly by conventional methods (Fatt & Katz, 1951). For focal recording of nerve terminal action potentials and e.p.ps, end-plate regions were localized by recording miniature end-plate potentials (m.e.p.ps) extracellularly (Hubbard & Schmidt, 1963 Laskowski & Thies, 1972 (Braun, Schmidt & Zimmermann, 1966;Miledi & 2ms Thies, 1971; Hurlbut, Longnecker & Mauro, 1971). In the experiment illustrated in Figure lb, (Sacchi & Perri, 1973;McLachlan, 1975 …”

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confidence: 99%

Can Barium Support the Release of Acetylcholine by Nerve Impulses?

Silinsky

1977

British J Pharmacology

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Conventional electrophysiological techniques were used to study the effects of Ba on the release of acetylcholine (ACh) from frog motor nerve terminals. Equimolar substitution of Ba for Ca eliminated end‐plate potentials (e.p.ps) without a corresponding decline in the amplitude of the nerve terminal action potential. Miniature end‐plate potentials (m.e.p.ps) were readily detectable in Ba solutions despite a depolarized muscle membrane. Studies on the e.p.p in curarized preparations bathed with different concentrations of Ca and Ba suggest that Ba may compete with Ca in the process by which depolarization of the nerve terminal leads to the release of ACh. Repetitive nerve stimulation at 1 Hz in Ba solutions caused 5–20 fold increases in m.e.p.p frequencies (7 experiments). Stimulation of Ba‐bathed preparations at 10 Hz elevated m.e.p.p frequencies to very high levels that could not be measured accurately (»100/s). It is suggested that the asynchronous discharge of m.e.p.ps produced by repetitive nerve stimulation is the electrophysiological correlate of the evoked ACh outflow in Ba solutions detected previously by bioassay of the perfusion fluid.

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Interactions Between Calcium and Barium on the Spontaneous Release of Transmitter From Mammalian Motor Nerve Terminals

Cited by 13 publications

References 20 publications

The effects of strontium and barium ions at synapses in sympathetic ganglia.

The effects of strontium and barium ions at synapses in sympathetic ganglia.

Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.

Can Barium Support the Release of Acetylcholine by Nerve Impulses?

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