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Journal of the Graduate Research Center

Abstract

Anderson (1964) has observed that migrating plasmodia of the slime mold, Physarum polycephalum, maintain a higher concentration of K+ in the region of the advancing front than in the posterior trailing region. He has also found that most of the Na- but little of the K+ in the posterior region can be removed by flushing water over the organism. Previous work by Anderson (1962) had revealed that alcohol precipitates prepared from plasmodial homogenates contain considerable quantities of K- which cannot be removed by washing. Based on these discoveries he has suggested that K+, but not Na+ is closely associated with some cytoplasmic component. Regarding the elusive problem of protoplasmic streaming, the occurrence of higher K+ concentrations in the advancing front of this organism lends support to the concept that this region plays a dominant role in the generation of ameboid motility (Allen, 1961). Kamiya (1965) has demonstrated that the front is a fibril-containing region and a site of contraction in glycerinated models of slime mold plasmodia. Of perhaps greater importance, Anderson's findings and conclusions challenge certain time-honored concepts which are of general physiological significance. It would appear that most investigators presuppose the cell to be a membrane-bound sac containing ions, particularly monovalent ones, in free solution. Since the movement of these ions across living membranes is frequently against a concentration gradient and cannot be accounted for by free diffusion, it has been necessary to postulate the existence of ion pumps and various schemes of active transport. Such metabolically dependent systems have been demonstrated to be thermodynamically impossible and to contradict experimental data (Ling, 1965; Ling, 1965a). Evidence supporting the view that monovalent cations can be complexed is frequently encountered in the literature (Ling, 1965; Ling, 1965a). The findings of Cope (1967) demonstrate convincingly that large quantities of Na+ are complexed by muscle and other tissues. His data reveal that a gel-like state is necessary for the type of cation-binding studied. Cope concludes that such complexing is a consequence of the low activity of water in gels or concentrated suspensions of anions. According to this concept, much of the interstitial water of such materials would be present in hydration shells and the solubility of small ions correspondingly reduced. It is the purpose of the present study to test severely the K+ binding capacity of dried plasmodial powders by subjecting them to prolonged dialysis. In accordance with Cape's findings the relationship between K+complexing and the concentration of dialyzed material is also explored.

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