Functional significance of localization of the Na channel in retinal A2 amacrine cells

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 15500289
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Neurophysiology and muscle physiology
• Research Institution: Saitama Medical School
• Principal Investigator: WATANABE Shu-ichi Saitama Medical School, Physiology, Professor, 医学部, 教授 (60138120)
• Co-Investigator(Kenkyū-buntansha): TAMALU Fuminobu Saitama Medical School, Physiology, Research Associate, 医学部, 助手 (70337541) ; ARITA Kazue Saitama Medical School, Physiology, Assistant Professor, 医学部, 講師 (80212645) ; NAKAHIRA Kansuke Saitama Medical School, Physiology, Assistant Professor, 医学部, 講師 (10260043) ; KANEKO Yuko Saitama Medical School, Physiology, Research Associate, 医学部, 助手 (60342771)
• Project Period (FY): 2003 – 2005
• Keywords: retina / AII amacrine cell / action potential / voltage-dependent Na channel / messenger RNA / glutamate / localization / parvalbumin

Research Abstract

Retinal AII amacrine cells transmit light information from rod bipolar cells to cone bipolar cells. It has been reported that AII amacrine cells generate action potentials of 10-20 mV in amplitude. In the present research, we elucidated (1)detailed properties of action potentials generated in the AII amacrine cell, (2)localization of the Na current within the AII amacrine cell, and (3)localization of Nav subunit within the retina. We obtained following results.
(1)(by Tamalu & Watanabe) Frequency of the action potential was 1)decreased depending on the concentration of glutamate locally applied to the dendrite of the rod bipolar cells, 2)increased depending on the concentration of glutamate locally applied to the arboreal dendrites of the AII amacrine cell, 3)increased depending on the intensity of injected current into the soma.
(2)(by Tamalu) TTX locally applied to the lobular appendage and soma most strongly inhibited the Na current compared to the application to the arboreal dendrite. Therefore, Nav may distribute mainly around the lobular appendage where voltage-dependent Ca channels are mostly localized. Also we found that activation voltage of the Ca current coincides with voltage range of the action potential.
(3)(by Kaneko, Arita & Nakahira) In situ hybridization (ISH) experiments revealed that Nav 1.1 were localized in cells that had the soma on the border between the inner nuclear layer and inner plexiform layer. Double staining of antibodies against parvalbumin (a marker of the AII amacrine cell) and ISH showed that Nav 1.1 expressing cells were parvalbumin-immunopositive cells.
In conclusion we found that (1)intensity of the light is coded by frequency of the action potential, that (2)Nav subtype expressed in the AII amacrine cell is Nav 1.1, that (3)Nav are localized around the output synapse, and that (4)the action potential is generated around the output synapse and facilitates activation of voltage-dependent Ca channels.