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The Journal of Neuroscience, December 15, 2002, 22(24):10533-10538

BRIEF COMMUNICATION
Elementary Properties of Axonal Calcium Currents in Type B Photoreceptors in Hermissenda crassicornis

Catherine T. Tamse¹ and Ebenezer N. Yamoah^{1, 2}

¹ Center for Neuroscience, Department of Otolaryngology, University of California, Davis, Davis, California 95616, and ² Marine Biological Laboratory, Woods Hole, Massachusetts 02543

Axons of the type B photoreceptors form synapses with hair cells and interneurons that are involved in classical conditioning in Hermissenda. We examined the differences in the Ca²⁺ channels expressed in the soma and axons of the B photoreceptors by direct functional recordings of single-channel currents. Although the soma of the B cells express two Ca²⁺ current subtypes, a transient BayK 8644-insensitive (~17 pS) current and a sustained BayK 8644-sensitive (~10 pS) current, the axons expressed only the latter. The axonal Ca²⁺ current activated at potentials positive to 20 mV. Moreover, the Ca²⁺ channels are distributed heterogeneously along the length of the axon, with the higher channel density (~10-15 channel µm²) occurring at the distal one-third of the isolated axons, with respect to the soma. The regions of Ca²⁺ channel clusters may represent the presynaptic site of the photoreceptor-interneuron synapses. Furthermore, the high-density clusters of Ca²⁺ channels may augment postsynaptic responses. The results of the present study represent the first direct recordings of Ca²⁺ currents at presumed synaptic sites. Expression of different Ca²⁺ channel subtypes at distinct compartments of the type B photoreceptors may generate diverse Ca²⁺ domains that may be required for neuronal plasticity in Hermissenda.

Key words: learning; memory; calcium currents; presynaptic calcium channels; photoreceptors; neuronal plasticity; Hermissenda

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Copyright © 2002 Society for Neuroscience  0270-6474/02/222410533-06$05.00/0

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