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Some properties of inward currents and spontaneous excitation of the cell membrane in smooth muscle

Research Project

Project/Area Number 06670053
Research Category

Grant-in-Aid for General Scientific Research (C)

Allocation TypeSingle-year Grants
Research Field General physiology
Research InstitutionNagoya University

Principal Investigator

NAKAYAMA Shinsuke  Nagoya University School of Medicine Department of Physiology Lecturer, 医学部, 講師 (30192230)

Co-Investigator(Kenkyū-buntansha) 富田 忠雄  名古屋大学, 医学部, 教授 (50078763)
Project Period (FY) 1994 – 1995
Project Status Completed (Fiscal Year 1995)
Budget Amount *help
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1994: ¥1,200,000 (Direct Cost: ¥1,200,000)
KeywordsSmooth muscle / Electrophysiology / Patch clamp / Inward current / Calcium channels / Kinetics / カルシウムチャネル / イオン電流
Research Abstract

1.The mechanisms underlying spontaneous excitation in smooth muscle are important, but not resolved. However, there are very few reports describing how ionic currents cause spontaneous excitation in smooth muscle cell membranes. In this study, we used enzymatically isolated smooth muscle cells to investigate the characteristics of inward Ca^<2+> current which is usually thought to be responsible to spike activities during the action potential.
2.In guinea-pig detrusor smooth muscle cells, whole-cell patch clamp experiments revealed that when large preconditioning depolarizations (e.g.+80 mV,5 sec) were applied prior to a test step (0 mV,100 msec), test currents were suppressed by only a small amount. Further, subsequent repolarizations to the holding potential (+60 mV) induced very slowly (tau-10 msec) deactivating Ca^<2+> tail currents.
3.This phenomenon can be explained by a model in which Ca^<2+> channels are transfered from the normal to a second open state during large depolarizing steps. In the second open state Ca^<2+> channels are not inactivated and deactivate very slowly.
4.Using cell-attached patch clamp techniques (50-100 mM Ba^<2+> in the pipette), we recorded single channel currents corresponding to the second open state. After a large depolarization tp transfer Ca^<2+> channels to the long open state, we applied a ramp pulse to measure I-V relationship of unitary Ca^<2+> channel current. The slope conductance was 22-30pS which is similar to that in the normal open state.
5.Similar results were obtained from other smooth muscles (e.g.guinea-pig stomach, taenia caeci). The second open state seems to be a common mechanism in smooth muscles, and may play an important role in persistent Ca^<2+> influx and subsequent excitation of the cell membrane in smooth muscle.

Report

(3 results)
  • 1995 Annual Research Report   Final Research Report Summary
  • 1994 Annual Research Report
  • Research Products

    (10 results)

All Other

All Publications (10 results)

  • [Publications] NAKAYAMA,S.: "Does the formation of the calcium tail current involve voltage-dependent phosphorylation?" Japanese Journal of Physiology. 45,. S106. (1995)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1995 Final Research Report Summary
  • [Publications] IINO,S.: "Intracellular calcium ions and intracellular pH in smooth muscle of rabbit portal vein." Japanese Journal of Physiology. 45,. S106. (1995)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1995 Final Research Report Summary
  • [Publications] NAKAYAMA,S.: "Evidence for long open states of the Ca^<2+> channel induced by large depolarizations in the presence or absence of Bay K 8644 in guinea-pig detrusor cells." British Journal of Pharmacology. (submitted).

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1995 Final Research Report Summary
  • [Publications] NAKAYAMA,S., SMITH,L.M.& TOMITA,T.: "Does the formation of the calcium tail current involve voltage-dependent phosphorylation?" Jpn.J.Physiol.45. S106 (1995)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1995 Final Research Report Summary
  • [Publications] IINO,S., HAYASHI,H., NAKAYAMA,S.& TOMITA,T.: "Intracellular calcium ions and intracellular pH in smooth muscle of rabbit portal vein." Jpn.J.Physiol.45. S106 (1995)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1995 Final Research Report Summary
  • [Publications] NAKAYAMA,S.& BRADING,A.F.: "Evidence for long open states of the Ca^<2+> channel induced by large depolarizations in the presence or absence of Bay K 8644 in guinea-pig detrusor cells." Br.J.Pharmacol.(submitted).

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1995 Final Research Report Summary
  • [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. (in press).

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1995 Final Research Report Summary
  • [Publications] NAKAYAMA,S.: "Does the formation of the calcium tail current involve valtage-dependent phosphorylation?" Japanese Journal of Physiology. 45. S106.

    • Related Report
      1995 Annual Research Report
  • [Publications] IINO,S.: "Intracellular calcium ions and intracellular pH in smooth muscle of rabbit portal vein." Japanese Journal of Physiology. 45. S106. (1995)

    • Related Report
      1995 Annual Research Report
  • [Publications] NAKAYAMA,S.: "Smooth muscle excitation" Academic Press eds.Bolton,T.B.& Tomita,T., 10 (1996)

    • Related Report
      1995 Annual Research Report

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Published: 1994-04-01   Modified: 2016-04-21  

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