Effects of extracellular sodium on calcium efflux and membrane current in single muscle cells from the barnacle.
AUTOR(ES)
Lederer, W J
RESUMO
The actions of extracellular sodium (Nao) on membrane potential, membrane current, membrane conductance and Ca efflux were examined in single muscle cells from the giant barnacle, Balanus nubilus. The intracellular compartment was perfused to facilitate the control of intracellular constituents including calcium ions (Ca2i+). Changing Nao has no large effect on Ca efflux when free intracellular calcium activity, [Ca2+]i, is low (about 0.1 microM). However, increasing [Ca2+]i leads to the development of Nao-dependent Ca efflux as well as to an augmentation in Nao-independent Ca efflux. Reducing Nao (using Li+ as a substitute cation) leads to a depolarization of the membrane when [Ca2+]i is low (about 0.1 microM). Increasing [Ca2+]i causes the membrane to depolarize. With [Ca2+]i at about 10.0 microM, reduction of Nao produces a hyperpolarization of the membrane. Significant Nao-dependent inward current is seen when [Ca2+]i is high. This current is large with respect to the Nao-dependent changes in Ca efflux (about 1 microA per p-mole/sec). The Ca2i+-activated, Nao-dependent changes in Ca efflux and membrane current are not sensitive to La3o+. However, Lao3+ does inhibit a fraction of the Cai2+-activated changes in membrane current and Ca efflux which are not dependent on Nao. Over a limited range of membrane potential Ca efflux is not voltage-dependent. Possible relationships between the Nao-dependent changes in Ca efflux and Nao-dependent changes in membrane potential or current are discussed. We find that these changes cannot be readily interpreted in terms of a single transport mechanism.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1195337Documentos Relacionados
- Sodium pump stoicheiometry determined by simultaneous measurements of sodium efflux and membrane current in barnacle.
- Extracellular divalent and trivalent cation effects on sodium current kinetics in single canine cardiac Purkinje cells.
- Further observations on the behaviour of ouabain-insensitive sodium efflux towards proctolin in barnacle muscle fibres.
- Stimulation by injected guanosine triphosphate of the sodium efflux in barnacle muscle fibres.
- Effect of pentachlorophenol on calcium accumulation in barnacle muscle cells.