視細胞シナプス終末におけるカルシウムイオン濃度制御に関するコンピュータシミュレーション解析

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Photoreceptors of the vertebrate retina are known to release the neurotransmitter in the dark and decrease the rate of neurotransmitter release during the graded hyperpolarization in response to the light. To transmit such graded signal to the second order neurons, intracellular Ca2+ concentration ([Ca2+]i) of the photoreceptor terminal is considered to be regulated with the level of hyperpolarization. The purpose of the present study is to elucidate how [Ca2+]i of the cone photoreceptor terminal is regulated by the Ca2+ conductance and the plasma membrane calcium ATPase (PMCA) with the aid of computer simulations. Physiologically realistic models of the Ca2+ conductance and the PMCA of the mammalian cone photoreceptor inner segment were reconstructed from the voltage clamp and Ca2+ imaging experiments which were carried out on the isolated photoreceptor inner segments in previous studies. The physiological ranges of parameters of the model equations describing the voltage-gated calcium channels were estimated by referring to previous experiments. The parameters of the model equation describing the PMCA were estimated by assuming steady levels of [Ca2+]i. Dynamical change of [Ca2+]i at the terminal region was calculated using the estimated parameters. When the conductance and PMCA are evenly distributed in entire model terminal, [Ca2+]i was reduced from 1-2µM to 30nM in response to a voltage change from -45mV to -55mV which is relevant to the light-induced hyperpolarization to moderate light. The model of physiological mechanisms developed in the present study can be used to elucidate the underlying mechanisms of the light-induced response of the cone photoreceptor terminal in situ.
日本神経回路学会の論文
2005-12-05

視細胞シナプス終末におけるカルシウムイオン濃度制御に関するコンピュータシミュレーション解析

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