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Modulation of Ca 2+ ‐dependent Cl − channels by calcineurin in rabbit coronary arterial myocytes
Author(s) -
Ledoux Jonathan,
Greenwood Iain,
Villeneuve Louis R.,
Leblanc Normand
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.043836
Subject(s) - calcineurin , myocyte , dephosphorylation , chemistry , phosphatase , intracellular , patch clamp , biophysics , extracellular , calmodulin , endocrinology , medicine , biochemistry , phosphorylation , biology , receptor , enzyme , transplantation
The role of the Ca 2+ ‐dependent phosphatase calcineurin (CaN) in the modulation of Ca 2+ ‐dependent Cl ‐ channels (Cl Ca ) was studied in freshly isolated rabbit coronary arterial myocytes. Immunocytochemical experiments showed that calmodulin‐dependent protein kinase II (CaMKII) and CaN were distributed evenly throughout the cytoplasm of coronary myocytes at rest and translocated to the plasmalemma when intracellular Ca 2+ was increased. Cl Ca currents ( I Cl(Ca) ) elicited by cell dialysis with fixed intracellular Ca 2+ levels up to 500 n m were inhibited by 10 μ m cyclosporin A (CsA), a specific inhibitor of CaN, in a voltage‐dependent manner, whereas currents evoked by 1 μ m Ca 2+ were not affected. Inhibition of CaN with CsA also led to a significant reduction in Ca 2+ sensitivity of the channel at +50 mV; half‐maximal activation increased from 363 ± 16 n m Ca 2+ in control to 515 ± 40 n m Ca 2+ in the presence of CsA. Similar effects were observed on I Cl(Ca) when a specific peptide fragment inhibitor of CaN (CaN‐AF, 5 μ m ) was dialysed into the cell via the pipette (500 n m Ca 2+ ). Application of KN‐93 (10 μ m ), a specific inhibitor of CaMKII, enhanced I Cl(Ca) in myocytes dialysed with 1 μ m Ca 2+ but produced no significant effect on this current when the cells were dialysed with 350 or 500 n m Ca 2+ . These results are consistent with the notion that in coronary arterial cells, the activity of Cl Ca is enhanced by dephosphorylation of the channel or a closely associated regulatory protein. Moreover the balance of CaN and CaMKII regulating I Cl(Ca) is dependent on the level of Ca 2+ used to activate I Cl(Ca) .