An action potential-induced and ryanodine sensitive calcium transient dynamically regulates transmitter release at
T W Dunn1, E A Montgomery, N I Syed
1Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
Abstract:
The notion that calcium released through ryanodine receptors effects presynaptic neurotransmitter release is gaining acceptance with the observation that this calcium does indeed contribute to both action potential-evoked and spontaneous transmitter release in a variety of preparations. However, the dynamics of this calcium release and its impact on transmitter release has not yet been fully elucidated. Moreover, in contrast to vertebrate synapses, much less is known about the involvement of ryanodine receptors in the regulation of transmitter release at invertebrate synapses. In this study, we reconstructed specific synapses between individually identifiable preand postsynaptic neurons from Lymnaea to demonstrate that although ryanodine reduces the amplitude of the action potential-induced calcium transient, it does not however, alter the resting calcium level. These data suggest that action potential-induced calcium release through ryanodine receptors is fast and highly dynamic and in turn regulates transmitter release at reconstructed synapses between Lymnaea neurons. This study thus provides direct evidence that a dynamic ryanodine receptor-mediated calcium transient occurs with the presynaptic action potential.
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