Calcium-binding of synaptosomes isolated from rat brain cortex
Tóm tắt
Ca++ concentration in the synaptosomal suspension was measured to determine the liberation from and binding to isolated brain cortex synaptosomes by utilizing a dual wavelength spectrophotometer to monitor the absorbance changes of murexide raised by Ca++. When synaptosomes were suspended in isotonic solutions of a NaCl−KCl mixture containing more than 30 to 40mM of KCl, a marked liberation of calcium ion was observed in proportion to the rise in KCl concentration, whereas there was rarely any significant release of Ca++ observed with an external KCl concentration of less than 20mM. Titration of the synaptosomal suspension with Ca++ revealed that, in the absence of external K+, a part of added Ca++ was almost instantaneously bound to the synaptosomal particles so far as these particles had not been saturated with Ca++. Such a Ca++-binding was markedly depressed by a higher external K+ concentration. Ouabain and cyanide did not have that effect on such a K+-induced inhibition of Ca++-binding. The present results indicate that the inhibition of Ca++-binding by high external K+ concentration probably results from a change in synaptosomal membrane which is of a cooperative nature.
Tài liệu tham khảo
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