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Voltage‐dependent inactivation in a cardiac‐skeletal chimeric calcium channel
Author(s) -
Parent L,
Gopalakrishnan M,
Lacerda A.E,
Wei X,
Perez-Reyes E
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00090-v
Subject(s) - xenopus , calcium , protein subunit , chemistry , voltage dependent calcium channel , biophysics , n type calcium channel , r type calcium channel , calcium channel , skeletal muscle , biochemistry , biology , t type calcium channel , endocrinology , gene , organic chemistry
The loci for inactivation in calcium channel proteins are unknown. Mechanisms for inactivation may be distributed across Ca 2+ channel subunits and appear to be complex, multiple and interacting. We took advantage of the properties of chimeras, constructed between cardiac (H4) and skeletal muscle (Sk4) calcium channel α 1 subunits to study the molecular mechanism of inactivation in L‐type calcium channels. Sk1H3, a chimeric construct of these two L‐type calcium channels, was expressed in Xenopus oocytes in the absence of auxiliary subunits. Sk1H3 incorporated repeat I from skeletal muscle α 1 , and repeats II, III, IV from heart α 1 , subunit. Sk1H3 inactivated faster ( τ ≈ 300 ms) and more fully than the wild‐type H4 with Ba 2+ ions as the charge carrier. Thus, inactivation of Sk1H3 was 90% complete after a 5‐s conditioning pulse at +20 mV while inactivation of H4 was only 37% complete. Sk1H3 inactivation also developed at more negative potentials with E 0.5 = −15 mV as compared to E 0.5 = −5 mV for H4. In the presence of external calcium ions, the extent of inactivation significantly increased from 37 to 83% for H4 while inactivation of Sk1H3 was only slightly increased. Inactivation with Ba 2+ as the charge carrier was confirmed at the single‐ channel level where averaged single‐channel ensembles showed a similar rate of inactivation. Collectively, these observations demonstrate that Sk1H3 inactivation appears to have a prominent voltage‐dependent component. Whether Sk1H3 inactivation involves interactions within repeat I alone or interactions between repeat I and site(s) located in the three other repeats of the α 1 subunit has yet to be determined.