Open AccessThe Regulation of the Na + ‐Ca 2+ Exchanger of Heart Sarcolemma
Author(s) -
CARONI Pico,
CARAFOLI Ernesto
Publication year - 1983
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1983.tb07383.x
Subject(s) - calmodulin , sarcolemma , phosphatase , chemistry , adenosine triphosphate , enzyme , biophysics , calcium , biochemistry , biology , membrane , organic chemistry
The Na + /Ca 2+ ‐exchange of calf‐heart sarcolemma is activated by a treatment with ATP, Mg 2+ , and Ca 2+ , and deactivated by a treatment with phosphorylase phosphatase. The effect of th e latter can be substituted by a treatment with Mg 2+ , Ca 2+ , and calmodulin. the activating treatment does not require added calmodulin, but is inhibited by calmodulin antagonists. Evidently, engdogenous calmodulin is required and sufficient. Activation is half‐maximal at about 2μM Ca 2+ . Added clamodulin, however, decreases the K m (Ca 2+ ) of the activating process to about 0.8 μM. Deactivation is half‐maximal, at optimal calmodulin concentrations, at about 1.5 μM Ca 2+ . Experiments with adenosine 5′‐[γ‐thio]triphosphate have shown that the activating treatment is mediated by a kinase and the deactivating treatment by a phosphatase. The concerted operation of the two enzymes is made possible by their different Ca 2+ affinity. At saturating Ca 2+ concentrations, the level of ATP may also influence the balance of the two enzymes.