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- Title
Complex modulation of L-type Ca<sup>2+</sup> current inactivation by sorcin in isolated rabbit cardiomyocytes.
- Authors
Fowler, Mark R.; Colotti, Gianni; Chiancone, Emilia; Higuchi, Yoshiharu; Seidler, Tim; Smith, Godfrey L.
- Abstract
Modulation of the L-type Ca2+ channel (LTCC) by sorcin was investigated by measuring the L-type Ca2+ current ( ICa,L) in isolated rabbit ventricular myocytes using ruptured patch, single electrode voltage clamp in the absence of extracellular Na+. Fifty millimolars EGTA (170 nM Ca2+) in the pipette solution buffered bulk cytoplasmic [Ca2+], but retained rapid Ca2+-dependant inactivation of ICa,L,. Recombinant sorcin (3 μM) in the pipette significantly slowed time-dependant inactivation ( τfast: 8.8 ± 0.9 vs. 15.1 ± 1.7 ms). Sorcin had no significant effect on ICa,L, after inhibition of the sarcoplasmic reticulum (SR). Using 10 mM 1,2-bis( o- N, N, N′, N′-tetraacetic acid (170 nM Ca2+), ICa,L inactivation was then determined by a Ca2+ -independent, voltage-dependant process. Under these conditions, 3 μM sorcin speeded up inactivation. A similar effect was observed by substitution of Ca2+ with Ba2+. Down-regulation of endogenous sorcin to 27 ± 7% using an RNAi adenoviral vector slowed inactivation of ICa,L by ∼42%. The effects of sorcin on voltage-dependant inactivation were mimicked by a truncated form of the protein containing only the Ca2+-binding domain. This data is consistent with two independent actions of sorcin on the LTCC: (1) slowing Ca2+-dependant inactivation and (2) stimulating voltage-dependant inactivation. The net effect of sorcin on the time-dependent inactivation of ICa,L was a balance between these two effects. Under normal conditions, sorcin slows ICa,L inactivation because the effects of Ca2+-dependant inactivation out-weigh the effects on voltage-dependant inactivation.
- Subjects
RECOMBINANT proteins; HEART cells; RNA; SARCOPLASMIC reticulum; LABORATORY rabbits
- Publication
Pflügers Archiv: European Journal of Physiology, 2009, Vol 457, Issue 5, p1049
- ISSN
0031-6768
- Publication type
Article
- DOI
10.1007/s00424-008-0575-5