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Molecular determinant for run-down of L-type Ca2+ channels localized in the carboxyl terminus of the 1C subunit

K J Kepplinger1, G Förstner, H Kahr

  • 1Institute for Biophysics, University of Linz, A-4040 Linz, Austria.

The Journal of Physiology
|November 18, 2000
PubMed

Insights

The C-terminal sequence (1572-1651) of alpha1C subunits significantly impacts L-type calcium channel run-down. This region confers resistance to run-down and may be modulated by calpastatin.

Area of Science:

  • Molecular and Cellular Biology
  • Cardiovascular Physiology
  • Ion Channel Research

Background:

  • Calcium (Ca2+) channels are crucial for cellular function, and their activity can be modulated by various factors.
  • Channel 'run-down,' a decrease in channel activity over time, affects the reliability of Ca2+ channel studies and function.
  • The C-terminal tail of the alpha1C subunit is implicated in the regulation of L-type Ca2+ channel properties.

Purpose of the Study:

  • To investigate the role of the specific C-terminal sequence (residues 1572-1651) in the alpha1C subunit of Ca2+ channels.
  • To determine how alterations in this sequence affect the phenomenon of channel run-down.
  • To explore the potential involvement of calpastatin in modulating Ca2+ channel run-down.

Main Methods:

  • Functional characterization of wild-type and mutant alpha1C,77 and alpha1C,86 Ca2+ channel isoforms.
  • Co-expression of pore-forming alpha1C subunits with alpha2delta and beta2a subunits in HEK-tsA201 cells.
  • Electrophysiological recordings using whole-cell and single-channel patch-clamp techniques.
  • Western blot analysis to detect calpastatin expression.

Main Results:

  • Replacing amino acids 1572-1651 in alpha1C,77 with those from alpha1C,86 (creating alpha1C,86) significantly altered run-down, slowing it considerably.
  • Transferring specific segments (L: 1572-1598 or K: 1595-1652) from alpha1C,86 into alpha1C,77 did not fully replicate the resistance to run-down observed in alpha1C,86.
  • The protease inhibitor calpastatin, when added with ATP, could reverse the run-down of alpha1C,77 channels, and calpastatin expression was confirmed in the cells.

Conclusions:

  • The C-terminal sequence spanning residues 1572-1651 in the alpha1C subunit plays a critical role in regulating the run-down of L-type Ca2+ channels.
  • This specific sequence confers significant resistance to channel run-down.
  • Endogenous calpastatin is suggested as a potential modulator of Ca2+ channel run-down, targeting this C-terminal region.

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