Presynaptic mechanism of action induced by 5-HT in nerve terminals: possible involvement of ryanodine and IP3 sensitive 2+ stores |
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Authors: | Dropic Amanda J Brailoiu Eugen Cooper Robin L |
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Affiliation: | Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA. |
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Abstract: | Although modulation of transmitter release by serotonin (5-HT) at crayfish neuromuscular junctions has been known since 1965, the mechanisms of action have not been established in this classical synaptic preparation. We show that injections of adenophostin-A (an IP3 analog) in the nerve terminals greatly enhances synaptic transmission. Exposure to ryanodine (Ry) produces a biphasic response: at low concentration it is excitatory and high concentration it is inhibitory. Likewise, a low concentration (1 microM) of caffeine enhances synaptic transmission, whereas a high concentration (10 mM) has little effect on transmission. The varied responses and sensitivity to Ry and caffeine suggest a Ca(2+)-induced Ca(2+)-release mechanism and/or the presence of an IP3-receptor within the terminal. Thus, it is likely 5-HT's response is due to activation of intracellular pathways, which subsequently release Ca2+ from internal stores. |
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