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Pharmacological preconditioning by diazoxide downregulates cardiac L‐type Ca 2+ channels
Author(s) -
González G,
Zaldívar D,
Carrillo ED,
Hernández A,
García MC,
Sánchez JA
Publication year - 2010
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2010.00960.x
Subject(s) - diazoxide , channel blocker , chemistry , reactive oxygen species , membrane potential , pharmacology , cardioprotection , downregulation and upregulation , patch clamp , medicine , endocrinology , biophysics , biology , biochemistry , ischemia , calcium , receptor , organic chemistry , insulin , gene
BACKGROUND AND PURPOSE Pharmacological preconditioning (PPC) with mitochondrial ATP‐sensitive K + (mitoK ATP ) channel openers such as diazoxide, leads to cardioprotection against ischaemia. However, effects on Ca 2+ homeostasis during PPC, particularly changes in Ca 2+ channel activity, are poorly understood. We investigated the effects of PPC on cardiac L‐type Ca 2+ channels. EXPERIMENTAL APPROACH PPC was induced in isolated hearts and enzymatically dissociated cardiomyocytes from adult rats by preincubation with diazoxide. We measured reactive oxygen species (ROS) production and Ca 2+ signals associated with action potentials using fluorescent probes, and L‐type currents using a whole‐cell patch‐clamp technique. Levels of the α 1c subunit of L‐type channels in the cellular membrane were measured by Western blot. KEY RESULTS PPC was accompanied by a 50% reduction in α 1c subunit levels, and by a reversible fall in L‐type current amplitude and Ca 2+ transients. These effects were prevented by the ROS scavenger N‐acetyl‐L‐cysteine (NAC), or by the mitoK ATP channel blocker 5‐hydroxydecanoate (5‐HD). PPC signficantly reduced infarct size, an effect blocked by NAC and 5‐HD. Nifedipine also conferred protection against infarction when applied during the reperfusion period. Downregulation of the α 1c subunit and Ca 2+ channel function were prevented in part by the protease inhibitor leupeptin. CONCLUSIONS AND IMPLICATIONS PPC downregulated the α 1c subunit, possibly through ROS. Downregulation involved increased degradation of the Ca 2+ channel, which in turn reduced Ca 2+ influx, which may attenuate Ca 2+ overload during reperfusion.