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Is the mitochondrial Ca 2+ uniporter a voltage‐modulated transport pathway?
Author(s) -
Kapùs András,
Szászi Katalin,
Káldi Krisztina,
Ligeti Erzsébet,
Fonyó Attila
Publication year - 1991
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(91)80444-8
Subject(s) - protonophore , uniporter , biophysics , chemistry , valinomycin , membrane potential , cytosol , biochemistry , biology , enzyme
The influence of membrane potential (Δψ) on Ca 2+ transport through the Ca 2+ uniporter (UP) was investigated in fura‐2‐loaded rat heart mitochondria at physiologically relevant‐submicromolar‐external [Ca 2+ ]. In the absence of Δψ the UP could not mediate Ca 2+ uptake even when an 8‐fold external (∼500 nM) to internal (∼60 nM) [Ca 2+ ] gradient was present and charge compensation was provided by acetate and the protonophore, CCCP. A small (∼−120 mV) and transient Δψ (generated by valinomycin) resulted in a rise in matrix [Ca 2+ ] only when external [Ca 2+ ] exceeded 150 nM. At physiologically high (∼−180 mV) and stable Δψ this threshold value for Ca 2+ uptake dropped to 15 nM. The results indicate that (1) at physiological [Ca 2+ ] m Δψ in addition to being a component of Δμ Ca 2+ seems to be necessary for providing a transport‐competent conformation for the UP; and (2) below a threshold [Ca 2+ ] m the UP cannot operate even in the presence of a high electric driving force.