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Kinetics and Mechanism: Modulation of Ion Transport in the Cardiac Sarcolemma Sodium‐Calcium Exchanger by Protons, Monovalent Ions, and Temperature a c
Author(s) -
KHANANSHVILI DANIEL,
WEILMASLANSKY EVELYNE,
BAAZOV DAVID
Publication year - 1996
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1996.tb44789.x
Subject(s) - tel aviv , chemistry , medicine , library science , computer science
The cardiac sarcolemma Na+-CaZt exchange cycle and its partial reactions (Na+-Na' and CaZt-Ca2+ exchanges) can be described as separate movements of Nat and CaZt ions through the exchanger (consecutive or ping-pong mechanism).1-6 Although the electrogenic stoichiometry (3Na' : Ca2+) of ion exchange is electrogenic (one positive charge is translocated per one it is not clear how the net charge transfer is realized at various stages of the exchange cycle. It was suggested by several opportunities that the charged ion-protein intermediates can determine a response of the Na+-CaZt exchange rate to ~ o l t a g e , ~ , ' ~ ' ~ but these putative intermediates have not yet been identified and characterized. Whatever the exact mechanism is, three major factors can determine the overall rate and voltage response: a) the fractional concentration of rate-limiting intermediate(s); b) the magnitude of the rate constant that limits the overall exchange rate; c) the charge of rate-limiting intermediate(s). The rate-limiting pathway actually determines the identity of the predominant partial reaction and intermediates for controlling the rate and voltage-sensitive properties of exchange modes. According to the consecutive mechanism (SCHEME 1) the Na+-Ca2+ exchange and its partial reactions (Na+-Na+ and Caz+-Cazt exchanges) must involve common reaction routes ( e . g . , the CaZ+ influx for Na+-Ca2+ and Ca2+-CaZt