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Phosphorylation alters the pharmacology of Ca 2+ ‐activated Cl ‐ channels in rabbit pulmonary arterial smooth muscle cells
Author(s) -
Wiwchar M,
Ayon R,
Greenwood IA,
Leblanc N
Publication year - 2009
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.1476-5381.2009.00405.x
Subject(s) - phosphorylation , dephosphorylation , stimulation , niflumic acid , chemistry , biophysics , medicine , endocrinology , phosphatase , biochemistry , biology
Background and purpose: Ca 2+ ‐activated Cl ‐ currents (I Cl(Ca) ) in arterial smooth muscle cells are inhibited by phosphorylation. The Ca 2+ ‐activated Cl ‐ channel (Cl Ca ) blocker niflumic acid (NFA) produces a paradoxical dual effect on I Cl(Ca) , causing stimulation or inhibition at potentials below or above 0 mV respectively. We tested whether the effects of NFA on I Cl(Ca) were modulated by phosphorylation. Experimental approach: I Cl(Ca) was elicited with 500 nM free internal Ca 2+ in rabbit pulmonary artery myocytes. The state of global phosphorylation was altered by cell dialysis with either 5 mM ATP or 0 mM ATP with or without an inhibitor of calmodulin‐dependent protein kinase type II, KN‐93 (10 µM). Key results: Dephosphorylation enhanced the ability of 100 µM NFA to inhibit I Cl(Ca) . This effect was attributed to a large negative shift in the voltage‐dependence of block, which was converted to stimulation at potentials <−50 mV, ∼70 mV more negative than cells dialysed with 5 mM ATP. NFA dose‐dependently blocked I Cl(Ca) in the range of 0.1–250 µM in cells dialysed with 0 mM ATP and KN‐93, which contrasted with the stimulation induced by 0.1 µM, which converted to block at concentrations >1 µM when cells were dialysed with 5 mM ATP. Conclusions and implications: Our data indicate that the presumed state of phosphorylation of the pore‐forming or regulatory subunit of Cl Ca channels influenced the interaction of NFA in a manner that obstructs interaction of the drug with an inhibitory binding site.