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Functional evidence of a transmembrane channel within the Ca 2+ transport ATPase of sarcoplasmic reticulum
Author(s) -
de Meis Leopoldo,
Inesi Giuseppe
Publication year - 1992
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(92)80093-v
Subject(s) - efflux , endoplasmic reticulum , chemistry , thapsigargin , atpase , biophysics , vesicle , biochemistry , ion transporter , membrane , enzyme , biology
Ca 2+ efflux can be studied conveniently following dilution of sarcoplasmic reticulum (SR) vesicles preloaded with 45 Ca 2+ by active transport. The rates of efflux are highly dependent on ATPase substrates and cofactors (P i , Mg 2+ , Ca 2+ and ADP) in the efflux medium. On the other hand, pbenothiazines stimulate efflux through a passive permeability channel with no coupled catalytic events. Efflux activation by manipulation of catalytically active ATPase ligands, as well as by the catalytically inactive phenothiazines, can be prevented by thapsigargin, which is a highly specific inhibitor of the Ca 2+ ‐ATPase. This demonstrates that the passive channel activated by phenothiazines is an integral part of the ATPase, and can operate either uncoupled or coupled to catalytic events.