Document Type
Article
Original Publication Date
1984
Journal/Book/Conference Title
The Biophysical Journal
Volume
45
Issue
6
First Page
1135
Last Page
1144
DOI of Original Publication
10.1016/S0006-3495(84)84261-7
Date of Submission
February 2015
Abstract
Unidirectional calcium influx and efflux were evaluated in cardiac sarcoplasmic reticulum (SR) by 45Ca-"0Ca exchange at steady state calcium uptake in the absence of calcium precipitating anions. Calcium efflux was partitioned into a pump-mediated efflux and a parallel passive efflux by separately measuring passive efflux referable to the steady state. Unidirectional and net ATP-ADP fluxes were measured using [3H]-ATP -- ADP and [3H]- ADP -- ATP exchanges. Methods are presented that take into account changing specific activities and sizes of the nucleotide pools during the measurement of nucleotide fluxes. The contribution of competent and incompetent vesicles to the unidirectional and net nucleotide fluxes was evaluated from the specific activity of these fluxes in incompetent vesicles and from the fraction of vesicles that were incompetent. The results indicate that, in cardiac SR, unidirectional calcium fluxes are larger than the unidirectional nucleotide fluxes contributed by competent vesicles. Because the net ATPase rate of competent vesicles is similar to the parallel passive efflux, it appears that cardiac SR Ca-ATPase tightly couples ATP hydrolysis to calcium transport even at static head, with a coupling ratio near 1.0.
Rights
From The Biophysical Journal, Feher, J.J. and Briggs, F.N., Undirectional calcium and nucleotide fluxes in cardiac sarcoplasmic reticulum. II. Experimental results, Vol. 45, Page 1135. Copyright © 1984 The Biophysical Society. Published by Elsevier Inc. Reprinted with permission.
Is Part Of
VCU Physiology and Biophysics Publications
Comments
Originally published at http://dx.doi.org/10.1016/S0006-3495(84)84261-7
Under an Elsevier user license