Effects of silver ion on the calcium-induced calcium release channel in isolated sarcoplasmic reticulum.
Ag+-induced Ca2+ release in isolated sarcoplasmic reticulum (SR) was studied by the stopped flow method monitoring chlortetracycline fluorescence change. After improving the experimental procedure, the initial rate of Ca2+ release could be determined more precisely than before. Micromolar concentrations of Ag+ specifically enhanced Ca2+ efflux from heavy fraction of SR vesicles (HSR). This specific effect was referred to as Ag+-induced calcium release. The Ag+-induced Ca2+ efflux was activated by caffeine and ATP, but was inhibited by Mg2+ and procaine. Further, Ag+ enhanced the Ca2+-induced Ca2+ release over the whole range of Ca2+ concentrations, similarly to ATP. Parallel to Ca2+ efflux, Mg2+ efflux, measured by the same method, was also activated by Ag+. Choline permeability determined by the light scattering method was also activated by Ag+. The results suggest that Ag+ binds to the activation site of the Ca2+-induced Ca2+ release channel and opens the channel. The Ag+ binding site is different from the Ca2+ binding site but similar to the ATP binding site.
Tatsumi
S
S
Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University.
Suzuno
M
M
Taguchi
T
T
Kasai
M
M
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D002751:Chlortetracycline; D002794:Choline / Q000378:metabolism; D005453:Fluorescence; D008027:Light; D008274:Magnesium / Q000494:pharmacology; D010539:Permeability; D011343:Procaine / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D012834:Silver / Q000494:pharmacology*
D002120:Calcium Channel Agonists; D002110:Caffeine; D012834:Silver; D011343:Procaine; D000255:Adenosine Triphosphate; D008274:Magnesium; D002794:Choline; D002118:Calcium; D002751:Chlortetracycline