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Skeletal muscle L‐type Ca 2+ current modulation in γ1‐deficient and wildtype murine myotubes by the γ1 subunit and cAMP
Author(s) -
Held Brigitte,
Freise Doris,
Freichel Marc,
Hoth Markus,
Flockerzi Veit
Publication year - 2002
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.2001.012745
Subject(s) - myogenesis , chemistry , protein subunit , skeletal muscle , steady state (chemistry) , intracellular , patch clamp , biophysics , medicine , endocrinology , biology , biochemistry , receptor , gene
Modulation of the steady‐state inactivation and current amplitude by the γ1 subunit of the murine skeletal muscle L‐type Ca 2+ channel were investigated using the whole‐cell patch‐clamp technique. Transient expression of the γ1 subunit, but not of the γ2 (stargazin) protein, in primary cultured myotubes from γ1‐deficient mice shifted the steady‐state inactivation approximately −15 mV, thereby restoring wildtype (WT) steady‐state inactivation and current amplitude. The increased Ca 2+ current amplitude in γ1‐deficient cells was abolished in myotubes from animals of 4 weeks and older whereas the positive shift in steady‐state inactivation was independent of mouse age. Raising intracellular cAMP levels using the membrane‐permeant analogue 8‐Br‐cAMP led to an increase in Ca 2+ current amplitude in WT cells to the level in γ1‐deficient myotubes. There was no effect on the current amplitude in γ1‐deficient cells or on the steady‐state inactivation in either genotype. Rp‐cAMPS, a competitive inhibitor of cAMP‐dependent protein kinase, had no effect on the WT Ca 2+ current amplitude and steady‐state inactivation, but diminished the current amplitude in γ1‐deficient myotubes without affecting the steady‐state inactivation in these cells. These data show that the increased Ca 2+ influx in myotubes lacking the γ1 subunit, due to right‐shifted steady‐state inactivation and increased L‐type Ca 2+ current amplitude, is determined by the γ1 subunit. The effect on current amplitude depends on the age of the mice and its cAMP‐dependent modulation appears to be controlled by the γ1 subunit.