MOLECULAR FUNCTION OF CHIMERIC Ca-Na IONIC CHANNELS
Grant-in-Aid for Scientific Research (C)
|Allocation Type||Single-year Grants|
|Research Institution||OITA MEDICAL UNIVERSITY|
ONO Katsushige OITA MEDICAL UNIVERSITY, 医学部, 助手 (40253778)
ARITA Makoto OITA MEDICAL UNIVERSITY, 医学部, 教授 (60037364)
|Project Period (FY)
1995 – 1996
Completed(Fiscal Year 1996)
|Budget Amount *help
¥2,400,000 (Direct Cost : ¥2,400,000)
Fiscal Year 1996 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1995 : ¥1,500,000 (Direct Cost : ¥1,500,000)
|Keywords||COS CELL / PATCH CLAMP / Ca CHANNEL / alpha1 SUBUNIT / CONDUCTANCE / beta SUBUNIT / Na CHANNEL / α_1サブユニット|
BACKGROUND and OBJECTIVE
Recent electrophysiological studies combined with molecular biology provided evidence that the kinetics of the L-type Ca^<2+> channel derives largely from the structure of the pore-forming subunit of the channel (alpha_<1c> subunit), however, the molecular events underlying the formation of subconductance levels are still under investigation. To understand the nature and structural requirements for subconductance, we have expressed cardiac alpha_<1c> L-type Ca^<2+> channels with or without coexpression of the beta_2 subunit in COS cells or in Chinese Hamster Fibroblast (CHW) cells to determine if alpha_<1c> channels and alpha_<1c>/beta_2 channels display different single channel subconductance levels.
Transfection of COS- and CHW-cells : COS cells transiently transfected with cDNA encoding the alpha_1 subunit of the cardiac L-type calcium channel (alpha_<1c>), and CHW cells stably transfected with alpha_1 subunit alone or with alpha_<1c> plus cardiac beta
subunits (alpha_<1c>/beta_2), were maintained in cell culture (see below). Electrophysiology : Small (conventional) patch pipettes with resistances between 4-5 MOMEGA allowed recording of alpha_<1c>/beta_2 channels. Large (macropatch) pipettes with resistances between 0.2-0.3 MOMEGA allowed recording of alpha_<1c> channels. Patches were depolarized for 195 ms at every 0.5-1 seconds or for 395ms at every 5 seconds from a holding potential (V_H) of -80mV.In ramp clamp experiments, slope ratio of -0.1V/sec was applied at every 3 seconds.
(1) Structural requirements for the formation of subconducting state (s) of the L-type Ca^<2+> channel were studied in cardiac alpha_<1c> channels in COS- and CHW-cells with or without coexpression of beta_2-subunit.
(2) Similar four conductance levels were detected in alpha_<1c> alone and in alpha_<1c>/beta_2 channels : 3.4<plus-minus>0.2pS,6.4<plus-minus>0.2pS,14.5<plus-minus>0.2pS and 22.2<plus-minus>0.2pS
(3) Existence of pore-forming alpha_<1c> subunit alone fulfillls the condition to form multiple conducting states.
(4) Coexpression of beta_2-subunit leads to a higher probability of channel openings at three subconductance levels as well as full conducting level of 22 pS,but may not be prerequisite for production of sublevel openings in cardiac L-type Ca^<2+> channels. Less
Research Output (11results)