Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle

Autores
Hoya, Arturo; Venosa, Roque Alberto
Año de publicación
1995
Idioma
inglés
Tipo de recurso
artículo
Estado
versión publicada
Descripción
1. Fluxes studies were carried out to investigate the Na⁺-dependent outward movement of Ca²⁺ in intact frog sartorius muscle from Leptodactylus ocellatus, a preparation for which published data on the subject are sparse. 2. Under normal resting conditions the Na⁺-Ca²⁺ exchange was not readily detectable. 3. When muscles were exposed to 4 mM caffeine, the rate of fractional loss of Ca²⁺ (kCa,o) increased by about 50%. Most of this increase exhibits characteristics typical of the Na⁺-Ca²⁺ antiport working in the forward mode found in other cells. 4. The increase in kCa,o promoted by caffeine was decreased by: (a) 72% in the absence of external Na⁺ (Na⁺o); (b) 73% in Na⁺-loaded muscles ([Na⁺]i = 98 mM); (c) 70% when fibres were depolarized to -27 mV ([K⁺]o = 50 mM); and (d) 80% in the presence of 5 mM amiloride. 5. Ni²⁺ (5 mM), an inhibitor of the Na⁺-Ca²⁺ exchanger current, unexpectedly increased the caffeine-promoted rise in kCa,o. This effect of Ni²⁺ was associated with a concomitant caffeine-stimulated Ni²⁺ influx. In the absence of caffeine Ni²⁺ did not affect kCa,o. 6. It was concluded that: (a) under resting conditions the sarcolemmal Ca²⁺ pump suffices to handle the cytosolic calcium concentration ([Ca²⁺]i); (b) Na⁺-Ca²⁺ activity becomes apparent when [Ca²⁺]i is substantially increased by caffeine-induced Ca²⁺ release from the sarcoplasmic reticulum; and (c) the blocking effect of Ni²⁺ on the current generated by a Na⁺-Ca²⁺ exchange with a coupling ratio > 2 might actually represent a shift of the antiport mode toward an electroneutral 1Ni²⁺-1Ca²⁺ exchange.
Facultad de Ciencias Médicas
Materia
Medicina
Frog skeletal muscle
Caffeine
Medicinal chemistry
Na+-Ca2+ exchange
Nivel de accesibilidad
acceso abierto
Condiciones de uso
http://creativecommons.org/licenses/by-nc-sa/4.0/
Repositorio
SEDICI (UNLP)
Institución
Universidad Nacional de La Plata
OAI Identificador
oai:sedici.unlp.edu.ar:10915/123160

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network_name_str SEDICI (UNLP)
spelling Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscleHoya, ArturoVenosa, Roque AlbertoMedicinaFrog skeletal muscleCaffeineMedicinal chemistryNa+-Ca2+ exchange1. Fluxes studies were carried out to investigate the Na⁺-dependent outward movement of Ca²⁺ in intact frog sartorius muscle from <i>Leptodactylus ocellatus</i>, a preparation for which published data on the subject are sparse. 2. Under normal resting conditions the Na⁺-Ca²⁺ exchange was not readily detectable. 3. When muscles were exposed to 4 mM caffeine, the rate of fractional loss of Ca²⁺ (k<sub>Ca,o</sub>) increased by about 50%. Most of this increase exhibits characteristics typical of the Na⁺-Ca²⁺ antiport working in the forward mode found in other cells. 4. The increase in k<sub>Ca,o</sub> promoted by caffeine was decreased by: (a) 72% in the absence of external Na⁺ (Na⁺<sub>o</sub>); (b) 73% in Na⁺-loaded muscles ([Na⁺]<sub>i</sub> = 98 mM); (c) 70% when fibres were depolarized to -27 mV ([K⁺]<sub>o</sub> = 50 mM); and (d) 80% in the presence of 5 mM amiloride. 5. Ni²⁺ (5 mM), an inhibitor of the Na⁺-Ca²⁺ exchanger current, unexpectedly increased the caffeine-promoted rise in k<sub>Ca,o</sub>. This effect of Ni²⁺ was associated with a concomitant caffeine-stimulated Ni²⁺ influx. In the absence of caffeine Ni²⁺ did not affect k<sub>Ca,o</sub>. 6. It was concluded that: (a) under resting conditions the sarcolemmal Ca²⁺ pump suffices to handle the cytosolic calcium concentration ([Ca²⁺]<sub>i</sub>); (b) Na⁺-Ca²⁺ activity becomes apparent when [Ca²⁺]<sub>i</sub> is substantially increased by caffeine-induced Ca²⁺ release from the sarcoplasmic reticulum; and (c) the blocking effect of Ni²⁺ on the current generated by a Na⁺-Ca²⁺ exchange with a coupling ratio > 2 might actually represent a shift of the antiport mode toward an electroneutral 1Ni²⁺-1Ca²⁺ exchange.Facultad de Ciencias Médicas1995-08-01info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionArticulohttp://purl.org/coar/resource_type/c_6501info:ar-repo/semantics/articuloapplication/pdf615-627http://sedici.unlp.edu.ar/handle/10915/123160enginfo:eu-repo/semantics/altIdentifier/issn/0022-3751info:eu-repo/semantics/altIdentifier/doi/10.1113/jphysiol.1995.sp020839info:eu-repo/semantics/openAccesshttp://creativecommons.org/licenses/by-nc-sa/4.0/Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)reponame:SEDICI (UNLP)instname:Universidad Nacional de La Platainstacron:UNLP2025-09-29T11:29:18Zoai:sedici.unlp.edu.ar:10915/123160Institucionalhttp://sedici.unlp.edu.ar/Universidad públicaNo correspondehttp://sedici.unlp.edu.ar/oai/snrdalira@sedici.unlp.edu.arArgentinaNo correspondeNo correspondeNo correspondeopendoar:13292025-09-29 11:29:18.968SEDICI (UNLP) - Universidad Nacional de La Platafalse
dc.title.none.fl_str_mv Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
title Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
spellingShingle Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
Hoya, Arturo
Medicina
Frog skeletal muscle
Caffeine
Medicinal chemistry
Na+-Ca2+ exchange
title_short Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
title_full Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
title_fullStr Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
title_full_unstemmed Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
title_sort Characteristics of Na⁺‐Ca²⁺ exchange in frog skeletal muscle
dc.creator.none.fl_str_mv Hoya, Arturo
Venosa, Roque Alberto
author Hoya, Arturo
author_facet Hoya, Arturo
Venosa, Roque Alberto
author_role author
author2 Venosa, Roque Alberto
author2_role author
dc.subject.none.fl_str_mv Medicina
Frog skeletal muscle
Caffeine
Medicinal chemistry
Na+-Ca2+ exchange
topic Medicina
Frog skeletal muscle
Caffeine
Medicinal chemistry
Na+-Ca2+ exchange
dc.description.none.fl_txt_mv 1. Fluxes studies were carried out to investigate the Na⁺-dependent outward movement of Ca²⁺ in intact frog sartorius muscle from <i>Leptodactylus ocellatus</i>, a preparation for which published data on the subject are sparse. 2. Under normal resting conditions the Na⁺-Ca²⁺ exchange was not readily detectable. 3. When muscles were exposed to 4 mM caffeine, the rate of fractional loss of Ca²⁺ (k<sub>Ca,o</sub>) increased by about 50%. Most of this increase exhibits characteristics typical of the Na⁺-Ca²⁺ antiport working in the forward mode found in other cells. 4. The increase in k<sub>Ca,o</sub> promoted by caffeine was decreased by: (a) 72% in the absence of external Na⁺ (Na⁺<sub>o</sub>); (b) 73% in Na⁺-loaded muscles ([Na⁺]<sub>i</sub> = 98 mM); (c) 70% when fibres were depolarized to -27 mV ([K⁺]<sub>o</sub> = 50 mM); and (d) 80% in the presence of 5 mM amiloride. 5. Ni²⁺ (5 mM), an inhibitor of the Na⁺-Ca²⁺ exchanger current, unexpectedly increased the caffeine-promoted rise in k<sub>Ca,o</sub>. This effect of Ni²⁺ was associated with a concomitant caffeine-stimulated Ni²⁺ influx. In the absence of caffeine Ni²⁺ did not affect k<sub>Ca,o</sub>. 6. It was concluded that: (a) under resting conditions the sarcolemmal Ca²⁺ pump suffices to handle the cytosolic calcium concentration ([Ca²⁺]<sub>i</sub>); (b) Na⁺-Ca²⁺ activity becomes apparent when [Ca²⁺]<sub>i</sub> is substantially increased by caffeine-induced Ca²⁺ release from the sarcoplasmic reticulum; and (c) the blocking effect of Ni²⁺ on the current generated by a Na⁺-Ca²⁺ exchange with a coupling ratio > 2 might actually represent a shift of the antiport mode toward an electroneutral 1Ni²⁺-1Ca²⁺ exchange.
Facultad de Ciencias Médicas
description 1. Fluxes studies were carried out to investigate the Na⁺-dependent outward movement of Ca²⁺ in intact frog sartorius muscle from <i>Leptodactylus ocellatus</i>, a preparation for which published data on the subject are sparse. 2. Under normal resting conditions the Na⁺-Ca²⁺ exchange was not readily detectable. 3. When muscles were exposed to 4 mM caffeine, the rate of fractional loss of Ca²⁺ (k<sub>Ca,o</sub>) increased by about 50%. Most of this increase exhibits characteristics typical of the Na⁺-Ca²⁺ antiport working in the forward mode found in other cells. 4. The increase in k<sub>Ca,o</sub> promoted by caffeine was decreased by: (a) 72% in the absence of external Na⁺ (Na⁺<sub>o</sub>); (b) 73% in Na⁺-loaded muscles ([Na⁺]<sub>i</sub> = 98 mM); (c) 70% when fibres were depolarized to -27 mV ([K⁺]<sub>o</sub> = 50 mM); and (d) 80% in the presence of 5 mM amiloride. 5. Ni²⁺ (5 mM), an inhibitor of the Na⁺-Ca²⁺ exchanger current, unexpectedly increased the caffeine-promoted rise in k<sub>Ca,o</sub>. This effect of Ni²⁺ was associated with a concomitant caffeine-stimulated Ni²⁺ influx. In the absence of caffeine Ni²⁺ did not affect k<sub>Ca,o</sub>. 6. It was concluded that: (a) under resting conditions the sarcolemmal Ca²⁺ pump suffices to handle the cytosolic calcium concentration ([Ca²⁺]<sub>i</sub>); (b) Na⁺-Ca²⁺ activity becomes apparent when [Ca²⁺]<sub>i</sub> is substantially increased by caffeine-induced Ca²⁺ release from the sarcoplasmic reticulum; and (c) the blocking effect of Ni²⁺ on the current generated by a Na⁺-Ca²⁺ exchange with a coupling ratio > 2 might actually represent a shift of the antiport mode toward an electroneutral 1Ni²⁺-1Ca²⁺ exchange.
publishDate 1995
dc.date.none.fl_str_mv 1995-08-01
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
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language eng
dc.relation.none.fl_str_mv info:eu-repo/semantics/altIdentifier/issn/0022-3751
info:eu-repo/semantics/altIdentifier/doi/10.1113/jphysiol.1995.sp020839
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Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
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rights_invalid_str_mv http://creativecommons.org/licenses/by-nc-sa/4.0/
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