Premium
Inhibition of a mammalian large conductance, calcium‐sensitive K + channel by calmodulin‐binding peptides
Author(s) -
Braun A. P.,
Heist E. K.,
Schulman H.
Publication year - 2000
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 - 10.1111/j.1469-7793.2000.00479.x
Subject(s) - calmodulin , chemistry , biophysics , calcium , potassium channel , hek 293 cells , gating , tetraethylammonium , r type calcium channel , calcium channel , voltage dependent calcium channel , membrane potential , cytosol , n type calcium channel , biochemistry , ion channel , calcium activated potassium channel , t type calcium channel , biology , enzyme , receptor , potassium , organic chemistry
1 The large conductance, calcium‐sensitive K + channel (BK Ca channel) is a voltage‐activated ion channel in which direct calcium binding shifts gating to more negative cellular membrane potentials. We hypothesized that the calcium‐binding domain of BK Ca channels may mimic the role played by calmodulin (CaM) in the activation of calcium‐CaM‐dependent enzymes, in which a tonic inhibitory constraint is removed on CaM binding. 2 To examine such a hypothesis, we used peptides from the autoregulatory domains of CaM kinase II (CK291–317) and cNOS (the constitutive nitric oxide synthase; cNOS725–747) as probes for the calcium‐dependent activation of murine BK Ca channels transiently expressed in HEK 293 cells. We found that these CaM‐binding peptides produced potent, time‐dependent inhibition of mammalian BK Ca channel current following voltage‐dependent activation. Inhibition was observed in both the presence and the absence of cytosolic free calcium. 3 Similar application of CK291–31 had no effect on either the amplitude or kinetics of voltage‐dependent, macroscopic currents recorded from rabbit smooth muscle Kv1.5 potassium channels transiently expressed in HEK 293 cells. 4 Cytosolic application of both CK291–317 and tetraethylammonium (TEA) produced an additive and non‐competitive block of BK Ca current. This finding suggests that the peptide‐binding site is distinct (e.g. outside the pore region of the channel) from that of TEA. 5 Our results are thus consistent with a model in which the BK Ca channel's voltage‐dependent gating process is under an intramolecular constraint that is relieved upon calcium binding. The intrinsic calcium sensor of the channel may thus interact with an inhibitory domain present in the BK Ca channel, and by doing so, remove an inhibitory ‘constraint’ that permits voltage‐dependent gating to occur at more negative potentials.