Transfer of potassium. A new measure of cell-cell coupling.

Abstract

Mammalian cells of different species [human HF foreskin fibroblasts; Lesch-Nyhan LN fibroblasts; SV/HF transformed fibroblasts; human cervical cancer HeLa cells; Chinese hamster ovary CHO cells; baby hamster kidney BHK cells; mouse neoplastic L cells, 3T3 fibroblasts; mouse Terato Cl-25 ascites tumor cells] differ in sensitivity to ouabain. This sensitivity is expressed as reduced intracellular K+ content, reduced rates of protein synthesis and cessation of cell multiplication. Using 86Rb+ as a measure of intracelluar K+, higher levels of radioactivity were found in mixtures of ouabain-sensitive and -resistant cells cultured in the presence of ouabain than predicted from pure cultures of the 2 component cell types. The simplest explanation is that K+ and 86Rb+ are being transferred from ouabain-resistant to ouabain-sensitive cells, enhancing the total intracellular 86Rb+ in the culture. A function, index of cooperation, expresses this enhancement as a number ranging 0-1 and permits comparisons under various culture conditions and using various cell types. An index of cooperation > 0 requires cell contact, since no enhancement occurs when contact between 2 cell types in the same culture is prevented. The index of cooperation for a number of different cell combinations agrees with other measures of cell-cell interaction associated with gap junctions, i.e., electrical coupling and metabolic cooperation. Co-culture of ouabain-sensitive and ouabain-resistant cells in the presence of ouabain also leads to restoration of the capacity for protein synthesis. Autoradiography shows that this restoration occurs in the sensitive cell type and is dependent upon contact with ouabain-resistant cells. Sensitive cells multiply in the presence of ouabain when co-cultured with resistant cells. Thus K+, presumably transferred to sensitive cells through gap junctions, is able to counteract the toxic effects of ouabain on intracellular K+ levels and protein synthesis and to restore growth.