Inhibition of ryanodine binding to sarcoplasmic reticulum vesicles of cardiac muscle by Zn(2+) ions.
Using the assay of [(3)H]ryanodine binding to the sarcoplasmic reticulum, the effect of Zn(2+) on ryanodine receptors (RyRs) of cardiac muscle was investigated. There was no obvious change in the binding at [Zn(2+)](f) of less than 0.2 microM. However, a decrease of the binding became significant with raising [Zn(2+)](f) to 0.5 microM. The inhibitory effect of Zn(2+) was [Zn(2+)](f)-dependent, with IC(50/ZnI) of 2.1+/-0.4 microM (mean+/-S.D.). Scatchard analysis indicates that both an increase of K(d) and a decrease of B(max) were responsible for Zn(2+)-induced decrease of the binding. The Hill coefficient for this inhibitory effect of Zn(2+) was between 0.8 and 1.2. The interactions of the effects of Zn(2+) and various modulators of RyR indicate that the inhibitory effect of Zn(2+) was mostly mediated through inhibiting Ca(2+) activation sites (CaA) on RyR. Since the [Zn(2+)](f) dependence was not clearly changed by [Ca(2+)](f), the inhibitory effect of Zn(2+) may not be due to competition of Zn(2+) with Ca(2+) for CaA and probably is indirect. The inhibitory effect of Zn(2+) could not be antagonized by 2 mM dithiothreitol, a thiol-reducing agent, suggesting that the binding of Zn(2+) ions to RyRs of cardiac muscle is not accompanied by obvious change of redox state of the RyRs. In comparison with that seen in skeletal muscle [3], the effects of Zn(2+) on ryanodine binding to the sarcoplasmic reticulum of cardiac muscle show several distinct differences. It is indicated that the effect of Zn(2+) on RyRs may be isoform-dependent. The physiological significance of the effects of Zn(2+) is discussed.
Unit of Cell Signal Transduction, Shanghai Institute of Physiology, Chinese Academy of Sciences Shanghai, Shanghai, China.
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Wang
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Wei
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Cheng
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Chen
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Zhu
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D004229:Dithiothreitol / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D012433:Ryanodine / Q000737:chemistry / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry* / Q000187:drug effects* / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism*; D015032:Zinc / Q000008:administration & dosage* / Q000378:metabolism
D020033:Protein Isoforms; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D015032:Zinc; D002118:Calcium; D004229:Dithiothreitol