Discrimination of multiple binding sites for antagonists of the calcium release channel complex of skeletal and cardiac sarcoplasmic reticulum
The mechanisms by which ruthenium red (RR), neomycin and FLA 365 ([2,6-dichloro-4-aminophenyl]isopropylamine) inhibit calcium channels of skeletal and cardiac sarcoplasmic reticulum (SR) are characterized. Neomycin and FLA 365 inhibit ryanodine-enhanced calcium release from skeletal SR vesicles in a...
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Published in | The Journal of pharmacology and experimental therapeutics Vol. 262; no. 3; pp. 1028 - 1037 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Pharmacology and Experimental Therapeutics
01.09.1992
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Subjects | |
Online Access | Get full text |
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Summary: | The mechanisms by which ruthenium red (RR), neomycin and FLA 365 ([2,6-dichloro-4-aminophenyl]isopropylamine) inhibit calcium
channels of skeletal and cardiac sarcoplasmic reticulum (SR) are characterized. Neomycin and FLA 365 inhibit ryanodine-enhanced
calcium release from skeletal SR vesicles in a dose-dependent manner. The apparent affinity of [3H]ryanodine is reduced in
a dose-dependent manner by each inhibitor indicative of competitive mechanisms. Displacement studies with skeletal and cardiac
SR demonstrate that the order of inhibitory potency is RR greater than neomycin greater than FLA 365 and RR greater than FLA
365 greater than neomycin, respectively. Neomycin is 100-fold less potent in cardiac SR and inhibition of [3H]ryanodine binding
is biphasic in both tissues. Neomycin induces a greater proportion of [3H]ryanodine binding states recalcitrant to inhibition
in cardiac SR. The ability of neomycin to increase the apparent affinity of [3H]ryanodine for its binding sites is potentiated
by RR and attenuated by FLA 365. Kinetic binding studies reveal that increasing neomycin concentrations decreases the association
of [3H]ryanodine as predicted for competitive inhibition. However, high (much greater than Kn) neomycin increases [3H]ryanodine
binding affinity by slowing dissociation of the radioligand demonstrating that, like micromolar ryanodine, neomycin induces
allosterism. Studies with combinations of antagonists demonstrate the existence of two non-overlapping inhibitor recognition
sites within the ryanoid site, one polycationic inhibitor site and one FLA 365 inhibitor site. These results suggest that
aminoglycoside-induced muscle paralysis may be mediated by direct block of pre- and postsynaptic calcium release channels
of endoplasmic reticulum. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3565 1521-0103 |