期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1980
卷号：77
期号：11
页码：6912-6916
DOI：10.1073/pnas.77.11.6912
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Behavioral sensitization of the gill-withdrawal reflex of Aplysia is caused by presynaptic facilitation at the synapses of the mechanoreceptor sensory neurons of the reflex onto the motor neurons and interneurons. The presynaptic facilitation has been shown to be simulated by serotonin (the putative presynaptic facilitatory transmitter) and by cyclic AMP and to be accompanied by an increase in the Ca2+ current of sensory neuron cell bodies exposed to tetraethylammonium. This increase in the Ca2+ current could result from either a direct action on the Ca2+ channel or an action on an opposing K+ current. Here we report voltage clamp experiments which indicate that the increase in Ca2+ current associated with presynaptic facilitation results from a decrease in a K+ current. Stimulation of the connective (the pathway that mediates sensitization) or application of serotonin causes a decrease in a voltage-sensitive, steady-state outward current measured under voltage clamp as well as an increase in the transient net inward and a decrease in the transient outward currents elicited by brief depolarizing command steps. The reversal potential of the steady-state synaptic current is sensitive to extracellular K+ concentration, and both the steady-state synaptic current and the changes in the transient currents are blocked by K+ current blocking agents and by washout of K+. These results suggest that serotonin and the natural transmitter released by connective stimulation act to decrease a voltage-sensitive K+ current. The decrease in K+ current prolongs the action potential, and this in turn increases the duration of the inward Ca2+ current and thereby enhances transmitter release.
