The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum

X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release...

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Main Authors:	Scarpa, Antonio, Baldassare, Judith, Inesi, Giuseppe
Format:	Online
Language:	English
Published:	The Rockefeller University Press 1972
Online Access:	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2226096/

id	pubmed-2226096
recordtype	oai_dc
spelling	pubmed-22260962008-04-23 The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum Scarpa, Antonio Baldassare, Judith Inesi, Giuseppe Article X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release of calcium. Furthermore, net calcium accumulation by SR is prevented, when the ionophores are added to the reaction mixture before ATP. On the contrary, ATP-independent calcium binding to SR is not inhibited. This effect is specific for the two antibiotics and could not be reproduced, either by inactive derivatives, or by other known ionophores. Neither ionophore produces alterations of the electron microscopic appearance of SR membranes or inhibition of the calcium-dependent ATPase. In fact, the burst of ATP hydrolysis obtained on addition of calcium, is prolonged in the presence of the ionophores. Lanthanum inhibits ATP-independent calcium binding to SR, ATP-dependent calcium accumulation and calcium-dependent ATPase. However, addition of lanthanum to SR preloaded in the presence of ATP, does not cause calcium release. The reported experiments indicated that: (a) ATP-dependent calcium accumulation by SR results in primary formation of calcium ion gradients across the membrane. (b) Most of the accumulated calcium is not available for displacement by lanthanum on the outer surface of the membrane. (c) Calcium ionophores induce rapid equilibration of the gradients, by facilitating cation diffusion across the membrane. The Rockefeller University Press 1972-12-01 /pmc/articles/PMC2226096/ /pubmed/4264855 Text en Copyright © 1972 by The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
repository_type	Open Access Journal
institution_category	Foreign Institution
institution	US National Center for Biotechnology Information
building	NCBI PubMed
collection	Online Access
language	English
format	Online
author	Scarpa, Antonio Baldassare, Judith Inesi, Giuseppe
spellingShingle	Scarpa, Antonio Baldassare, Judith Inesi, Giuseppe The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
author_facet	Scarpa, Antonio Baldassare, Judith Inesi, Giuseppe
author_sort	Scarpa, Antonio
title	The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
title_short	The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
title_full	The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
title_fullStr	The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
title_full_unstemmed	The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum
title_sort	effect of calcium ionophores on fragmented sarcoplasmic reticulum
description	X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release of calcium. Furthermore, net calcium accumulation by SR is prevented, when the ionophores are added to the reaction mixture before ATP. On the contrary, ATP-independent calcium binding to SR is not inhibited. This effect is specific for the two antibiotics and could not be reproduced, either by inactive derivatives, or by other known ionophores. Neither ionophore produces alterations of the electron microscopic appearance of SR membranes or inhibition of the calcium-dependent ATPase. In fact, the burst of ATP hydrolysis obtained on addition of calcium, is prolonged in the presence of the ionophores. Lanthanum inhibits ATP-independent calcium binding to SR, ATP-dependent calcium accumulation and calcium-dependent ATPase. However, addition of lanthanum to SR preloaded in the presence of ATP, does not cause calcium release. The reported experiments indicated that: (a) ATP-dependent calcium accumulation by SR results in primary formation of calcium ion gradients across the membrane. (b) Most of the accumulated calcium is not available for displacement by lanthanum on the outer surface of the membrane. (c) Calcium ionophores induce rapid equilibration of the gradients, by facilitating cation diffusion across the membrane.
publisher	The Rockefeller University Press
publishDate	1972
url	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2226096/
_version_	1611436983959158784

The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum

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