Partial uncoupling of neurotransmitter release from [Ca2+]i by membrane hyperpolarization.
The dependence of evoked and asynchronous release on intracellular calcium ([Ca2+]i) and presynaptic membrane potential was examined in single-release boutons of the crayfish opener neuromuscular junction. When a single bouton was depolarized by a train of pulses, [Ca2+]i increased to different levels according to the frequency of stimulation. Concomitant measurements of evoked release and asynchronous release, from the same bouton, showed that both increased in a sigmoidal manner as a function of [Ca2+]i. When each of the depolarizing pulses was immediately followed by a hyperpolarizing pulse, [Ca2+]i was elevated to a lesser degree than in the control experiments, and the rate of asynchronous release and the quantal content were reduced; most importantly, evoked quantal release terminated sooner. The diminution of neurotransmitter release by the hyperpolarizing postpulse (HPP) could not be entirely accounted for by the reduction in [Ca2+]i. The experimental results are consistent with the hypothesis that the HPP reduces the sensitivity of the release machinery to [Ca2+]i, thereby not only reducing the quantal content but also terminating the quantal release process sooner.
Ravin
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The Otto Loewi Minerva Center for Cellular and Molecular Neurobiology, Department of Neurobiology, The Hebrew University, Jerusalem 91904, Israel.
Parnas
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Spira
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Parnas
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D000818:Animals; D003400:Astacoidea; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009469:Neuromuscular Junction / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*
D015220:Calcium Channels; D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents; D008274:Magnesium; D002118:Calcium; D016257:Fura-2