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COMPUTATIONAL STUDY OF THE HERMISSENDA B-PHOTORECEPTOR II: ROLE OF ACTION POTENTIAL DURATION IN SYNAPTIC FACILITATION
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M.C. Flynn*; Y. Cai;
D.A. Baxter; T. Crow
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| Dept Neurobiol/Anat, Univ Texas-Houston, Houston, TX, USA |
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Classical conditioning alters several properties of the B-photoreceptors in Hermissenda, including decreasing two K+ currents (IK,A & IK,Ca), decreasing a Ca2+ current (ICa), increasing the duration of the action potential (AP), and facilitating synaptic connections between medial B and medial A photoreceptors. The application of the K+ channel blocker 4-AP mimics several effects of conditioning in that it reduces IK,A, broadens APs and facilitates IPSPs. These results suggest that an increase in AP duration, which is induced by decreasing one or more K+ currents, may play a role in synaptic facilitation. To test this hypothesis, a mathematical model of a B-photoreceptor was developed and the influx of Ca2+ into the terminal compartment was measured during depolarizations of different durations. The durations of the depolarization mimicked the control AP duration (~10 ms) and the broadened AP following behavioral conditioning (~14 ms). A 40% increase in duration by itself lead to a 25% increase in Ca2+ influx. However, if this increase in duration was combined with a decrease in ICa, then the resulting Ca2+ influx decreased by 8%. These results suggest that any increases in Ca2+ influx that would be produced from AP broadening would be counter-acted by the simultaneous decrease in ICa observed with conditioning. Thus, a spike-duration independent (SDI) process is likely to contribute to facilitation following classical conditioning.
Supported by: Supported by NIH grant P01NS38310
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Citation for this abstract:
Flynn, M., Y. Cai, D.A. Baxter, and T. Crow (2001). Computational study of the Hermissenda B-photoreceptor II: Role of action potential duration in synaptic facilitation. Soc. Neurosci. Abstr. 27, 2532.
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