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Imaging of Ca²⁺ Dynamics Within the Presynaptic Terminals of Salamander Rod Photoreceptors

¹Department of Anatomy and Neurobiology, Neuroscience Institute, Morehouse School of Medicine and ²Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia

Submitted 19 November 2004; accepted in final form 7 August 2005

Although the overall importance of Ca²⁺ as a mediator of cell signaling and neurotransmitter release has long been appreciated, the details of Ca²⁺ dynamics within the inner segments of vertebrate rod photoreceptors are just beginning to be elucidated. Even less is known regarding Ca²⁺ dynamics within the rod presynaptic terminal compartment. Using fura-2 to report changes in intracellular Ca²⁺, we imaged the responses of enzymatically dissociated salamander rod photoreceptors retaining intact axons and presynaptic terminals stimulated with a brief depolarizing puff of KCl (30 mM pipette concentration). In the vast majority of cells, the response was a large increase in Ca²⁺ levels in the terminal compartment, but not in the soma. In contrast, rods exhibited a substantial elevation in somatic Ca²⁺ levels when depolarized with a brief puff of 100 mM KCl (pipette concentration). These data are consistent with previously reported differences in Ca²⁺ buffering mechanisms within the somatic and terminal compartments. Additionally, they may reflect the presence of Ca²⁺ channels having distinct properties within the membranes of the two compartments. Consistent with this hypothesis, fluorescent immunocytochemistry using an antibody against the L-type Ca²⁺ channel Ca_v1.2 (1C) subunit and semiquantitative confocal microscopy revealed a high concentration of immunoreactivity in the membranes of terminals of intact rods compared with the somata. Further investigations using enzymatically dissociated preparations of intact rod photoreceptors retaining their presynaptic terminals will allow further testing of these and other hypotheses regarding the compartmentalized regulation of Ca²⁺ dynamics within rod photoreceptors.

This article has been cited by other articles:

				P. R. MacLeish and C. A. Nurse Ion Channel Compartments in Photoreceptors: Evidence From Salamander Rods With Intact and Ablated Terminals J Neurophysiol, July 1, 2007; 98(1): 86 - 95. [Abstract] [Full Text] [PDF]