Abstract
The mechanism for extrusion of Na+ from Scenedesmus cells is characterized physiologically. It is stimulated by phosphate but oxygen is not necessary. Rb+ and Cs+ may also be extruded, but in the presence of Na+ they cannot compete for the sites on the inside of the transport system. When Na+ is extruded, Rb+ and, by inference, K+ seems to be transported as counter ion from the outside, and sodium ions compete only weakly for this external site. The parallelism between these findings and the Na+-K+-activated adenosine triphosphatases known from animal tissues is pointed out.
With low additions of phosphate, the extrusion mechanism can keep the cells practically free from Na+. Increasing the concentrations of external phosphate stimulates uptake more than extrusion, and a net uptake occurs. As for Rb+ and Cs+, they are taken up in the absence of external phosphate, but additions of P will greatly enhance the amounts absorbed. Two different ways of uptake are indicated.
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Selected References
These references are in PubMed. This may not be the complete list of references from this article.
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