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THE MEASUREMENT OF INTRACELLULAR SODIUM ACTIVITY AND ITS RELATIONSHIP TO THE ACTION OF CALCIUM IONS UPON THE LOW‐SODIUM CONTRACTURE IN FROG ATRIAL TRABECULAE
Author(s) -
Chapman R. A.,
Tunstall J.
Publication year - 1984
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1984.sp002842
Subject(s) - contracture , sodium , chemistry , biophysics , calcium , ion , relaxation (psychology) , intracellular , analytical chemistry (journal) , medicine , surgery , biochemistry , chromatography , biology , organic chemistry
If the Na concentration of the solution bathing a frog atrial trabecula is reduced a contracture rapidly develops and then relaxes spontaneously. If the Ca concentration of the low‐Na solution is raised during this relaxation a further contracture may develop. The amplitude of this Ca‐addition contracture depends in a complex manner upon [Na] o . It also shows a time dependence which is similar to the rate of spontaneous relaxation and the time course of the fall in a i Na as measured by ion‐sensitive micro‐electrodes. These observations are discussed in terms of transmembrane ion movements, the processes occurring during spontaneous relaxation and a possible compartmentalization of both intracellular Ca and Na ions. A relationship between [Na] i and [Na] o is derived from the contracture data that compares well with direct measurements made using ion‐sensitive micro‐electrodes.