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  • 1
    ISSN: 1432-2013
    Keywords: Key words  Patch clamp ; Calcium channel ; Run-down ; Cardiac myocyte ; Cytoplasm ; Calpastatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Using the patch clamp method we attempted to characterize the cytoplasmic factor in guinea-pig cardiac myocytes which restores L-type Ca2+ channel activity after run-down. The factor was eluted from a diethylaminoethyl (DEAE) sepharose column by KCl at 100–360 mM. On gel filtration the factor had an apparent molecular mass (M r) of 250–300 kDa. Two-dimensional electrophoresis of the partially purified factor showed at least nine spots, of which the major spot had a M r of about 100 kDa and an isoelectric point of 4.8, suggesting that the physicochemical properties of the factor resemble those of calpastatin, an endogenous inhibitor of Ca2+-activated protease, calpain. Calpastatin activity was increased in the partially purified cytoplasm and an antibody raised against calpastatin recognized the major band. Reduction of calpastatin in the cytoplasm decreased the potency of Ca2+ channel activation. These results suggest that calpastatin might interact with the Ca2+ channel and maintain channel activity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Key words Patch clamp ; Calcium channel ; Run-down ; Cardiac myocyte ; Cytoplasm ; Calpastatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We have found previously that run-down of cardiac Ca2+ channels in cell-free patches is reversed by cytoplasm plus adenosine triphosphate (ATP). Characterization of the factor in cytoplasm revealed that it is likely to be calpastatin (CS), an endogenous inhibitor of calpain (Ca2+-activated neutral protease). We therefore investigated the possible restoring effect of CS obtained from various tissues (activity 1.3–23 U/ml) on Ca2+ channel activity after run-down in inside-out patches. Although CS from porcine erythrocytes (plus 3 mM ATP) had only a minimal effect in restoring channel activity (to 4% of the control level recorded before the run-down), CS from porcine heart restored channel activity to 19% of control. The product of recombinant complementary deoxyribonucleic acid (cDNA) of human heart CS, a membrane-bound CS partially purified from bovine heart and CS from rabbit skeletal muscle (Sigma) restored channel activity to 28%, 23% and 10% of control levels, respectively. These results suggest that tissue-type CS, but not erythrocyte-type (truncated) CS, seems to have an effect on the cardiac Ca2+ channel to maintain its activity. Purified CS had relatively small effects compared to that of crude cytoplasm, implying that some other factor(s) might contribute also to the regulation of Ca2+ channel activity.
    Type of Medium: Electronic Resource
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