THE STRUCTURE OF MITOCHONDRIA IN ROD AND CONE PHOTORECEPTORS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goal of these studies is to develop a comprehensive structural and functional understanding of rod spherule and cone pedicle ribbon synaptic terminals. Vertebrate photoreceptors are nonspiking neurons that maintain sustained depolarization and neurotransmitter release from ribbon synapses in darkness and produce light-dependent graded hyperpolarizing responses. Rods transmit single photon responses with high fidelity, whereas cone exocytosis is faster. These come from differences in metabolic coupling and cross-talk between presynaptic photoreceptor mitochondria, endoplasmic reticulum (ER), plasma membrane Ca2+-ATPase (PMCA) and Na+-Ca2+ exchanger (NCX). We are determining the mechanisms of metabolic coupling in photoreceptor synapses. The specific aims of the laser scanning confocal microscopy (LSCM), electron microscopy (EM) and three-dimensional electron tomography (ET) studies are threefold. The first is to determine the cellular distribution and spatial interrelation of mitochondria, ER, PMCA and NCX in the retina and especially in the photoreceptor synaptic terminals. The second is to determine if the cellular and subcellular ATP and Ca2+ regulatory mechanisms differed between rod spherule and cone pedicle synaptic terminals. The third goal is to determine the functional significance of our results in relation to rod and cone synaptic terminal bioenergetics, Ca2+ homeostasis and neurotransmitter release.