1997 Fiscal Year Final Research Report Summary
Investigation into the long channel opening mechanism of the smooth muscle calcium channels
| Project/Area Number |
08670047
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General physiology
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| Research Institution | Nagoya University |
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Principal Investigator |
NAKAYAMA Shinsuke Nagoya Univ., Sch.of Med., Dept.Physiol., Assoc.Prof., 医学部, 助教授 (30192230)
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| Co-Investigator(Kenkyū-buntansha) |
KUZUYA Masafumi Nagoya Univ., Sch.of Med., Dept.Gerontol., Assistant Prof., 医学部, 助手 (10283441)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Smooth muscle / Calcium channels / Inward current / Kinetics / Patch clamp / Electrophysiology / Molecular biology / Phosphorylation |
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| Research Abstract |
L-type Ca^<2+> channels distributed in the smooth muscle plasma membrane are transferred into a long channel open state by applications of large depolarization. In the long open state, Ca^<2+> channels do not, or very slowly inactivate during depolarization, and deactivate slowly upon repolarization. Due to the non-inactivating feature the long channel open state may contribute to slow and tonic contractions in smooth muscle.
1996) Standard whole-cell patch clamp was applied to the smooth muscle cells enzymatically isolated from guinea-pig urinary bladder. Large depolarizations also transferred (L-type) Ca^<2+> channels into the long channel open state. This was confirmed by the formation of slow deactivating tail currents after large depolarizations (+80 to +100 mV,4-5 sec). Neither the inclusion of ATP-gamma-S in the patch pipette nor bath application of H-7 prevented the formation of the slow deactivating tail current. These results suggested that the transition of smooth muscle Ca^<2+> channel is not produced by a voltage-dependent phosphorylation process itself.
1997) Cell-attached patch clamp technique was applied to the CHO (Chinese hamster ovary) cells in which alpha_1-subunits (alpha_<1C-b>) of smooth muscle L-type Ca^<2+> channels are stably expressed. After large depolarizations (+80 to +100 mV,4 sec) closure of Ca^<2+> channel was significantly slowed. Since the patch pipette contained a high concentration of Bay K 8644, the long channel opening mechanism was considered distinct from so-called 'mode 2 gating'. Also, this result indicated that even the basic channel forming subunit of smooth muscle Ca^<2+> channel alone can produce multiple open states. Skeletal muscle beta-subunits (beta_<1a>), when co-expressed, suppressed Ca^<2+> channel opening upon repolarization. The probability of channel opening trace after large depolarization was restored by decreasing the duration of depolarization to 0.1-0.2sec.
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[Publications] NAKAYAMA,S., SMITH,L.M., TOMITA,T.& BRADING,A.F.: Multiple open states of calcium channels and their possible kinetic schemes. In Smooth muscle excitation, eds.Bolton, T.B.& Tomita, T.Academic Press, 13-25 (1996)
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