The cultured cell lines HeLa (human cervical carcinoma) and MDCK (renal epithelial) possess a trans-membrane K+ transport that can be pharmacologically divided into ouabain-sensitive, diuretic-sensitive and ouabain- and diuretic-insensitive components. The K+ transport of primary interest in this thesis is that sensitive to "loop" diuretic. Analysis of the cation and anion dependencies and "loop" diuretic sensitivity of this K+ transport indicates that it is mediated via a Na+ K+ Cl- "cotransporter" as has already been reported in other cell types. Cell shrinkage stimulated the diuretic-sensitive K+ transport in both HeLa and MDCK cells. Analysis of the Na+ K+ and Cl- dependency of this K+ flux demonstrated that this stimulation is principally due to an increase in the maximal velocity (Vmax) of this K+ transport. This stimulated K+ flux was not regulated by cAMP nor was the response modified by elevated cellular cAMP or by low extracellular Ca2+ (+ EGTA) media. The increased maximal velocity for K+ transport cannot simply be considered to be an absolute increase in the number of Na+ K+ Cl- cotransport units in the membrane. However, a possible regulation of the Na+ K+ Cl- "cotransport" turnover rate (molecules/site. second) may be Involved. In this study the Na+ K+ Cl- "cotransport" of both HeLa and MDCK cells was inhibited in metabolically depleted cells (metabolic inhibition induced by the limited-metabolisable sugar 2 deoxy-D-glucose). This effect may be considered a secondary response of cell swelling however, since exposure of metabolically depleted cells to hyperosmolar media re-activates the Na+ K+ C1- "cotransport" in both HeLa and MDCK cells.