[The isomorphism of univalent thallium and potassium in membrane transport processes].
Thallium ions (T1+) are able to isomorphous replacement of K+ in various minerals. The similarity between. T1+ and K+ is based upon the closeness of their crystal radii, hydration energy and mobility in aqueous solutions. Under certain conditions, the behaviour of T1+ can be substantially different from that of K+. As distinguished from K+, thallium ions tend to associate with different anions forming ion pairs and complexes. As a rule, the stability of these compounds is rather low, but in many cases the T(1+)-anion interactions appear to play an important role in discriminating between T1+ and K+ involved in transport processes. T1+/K(+)-selectivity characterizes K(+)-transport mechanisms operating in different kinds of cells membranes. In excitable membranes (muscles, nerves) the rates of passive transport of T1+ and K+ are similar. In non-excitable membranes (epithelial cells, red blood cells, mitochondrial membranes, bacteria) the T1+ passive permeability is about one or two orders of magnitude higher than that of K+. A moderate T1+/K(+)-selectivity was reported for various types of K+ active transport mechanisms.