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Calmodulin kinase and a calmodulin‐binding ‘IQ’ domain facilitate L‐type Ca 2+ current in rabbit ventricular myocytes by a common mechanism
Author(s) -
Wu Yuejin,
Dzhura Igor,
Colbran Roger J.,
Anderson Mark E.
Publication year - 2001
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.1469-7793.2001.t01-1-00679.x
Subject(s) - calmodulin , thapsigargin , camk , ryanodine receptor , phospholamban , protein kinase a , myocyte , biology , microbiology and biotechnology , chemistry , biophysics , endocrinology , medicine , endoplasmic reticulum , biochemistry , kinase , autophosphorylation , enzyme
1 Ca 2+ ‐calmodulin‐dependent protein kinase II (CaMK) and a calmodulin (CaM)‐binding ‘IQ’ domain (IQ) are both implicated in Ca 2+ ‐dependent regulation of L‐type Ca 2+ current (I Ca ). We used an IQ‐mimetic peptide (IQmp), under conditions in which CaMK activity was controlled, to test the relationship between these CaM‐activated signalling elements in the regulation of L‐type Ca 2+ channels (LTCCs) and I Ca in rabbit ventricular myocytes. 2 A specific CaMK inhibitory peptide nearly abolished I Ca facilitation, but the facilitation was ‘rescued’ by cell dialysis with IQmp. 3 IQmp significantly enhanced I Ca facilitation and slowed the fast component of I Ca inactivation, compared with an inactive control peptide. Neither effect could be elicited by a more avid CaM‐binding peptide, suggesting that generalized CaM buffering did not account for the effects of IQmp. 4 ICa facilitation was abolished and the fast component of inactivation eliminated by ryanodine, caffeine or thapsigargin, suggesting that the sarcoplasmic reticulum (SR) is an important source of Ca 2+ for I Ca facilitation and inactivation. IQmp did not restore I Ca facilitation under these conditions. 5 Engineered Ca 2+ ‐independent CaMK and IQmp each markedly increased LTCC open probability (P o ) in excised cell membrane patches. The LTCC P o increases with CaMK and IQmp were non‐additive, suggesting that CaMK and IQmp are components of a shared signalling pathway. 6 Both CaMK and IQmp induced a modal gating shift in LTCCs that favoured prolonged openings, indicating that CaMK and IQmp affect LTCCs through a common biophysical mechanism. 7 These findings support the hypothesis that CaMK is required for physiological I Ca facilitation in cardiac myocytes. Both CaMK and IQmp were able to induce a modal gating shift in LTCCs, suggesting that each of these signalling elements is important for Ca 2+ ‐CaM‐dependent LTCC facilitation in cardiac myocytes.