title: Relations between intracellular ion activities and extracellular osmolarity in Necturus gallbladder epithelium.
abstract: The interactions between ion and water fluxes have an important bearing on osmoregulation and transepithelial water transport in epithelial cells. Some of these interactions were investigated using ion-selective microelectrodes in the Necturus gallbladder. The intracellular activities of K+ and Cl- in epithelial cells change when the epithelium is adapted to transport in solutions of a low osmolarity. In order to achieve new steady states at low osmolarities, cells lost K+, Cl- and some unidentified anions. Surprisingly, the apparent K+ concentration remained high: at an external osmolarity of 64 mOsm the intracellular K+ concentration averaged 95 mM. This imbalance was sensitive to anoxia and ouabain. The effects of abrupt changes in the external osmolarities on the intracellular activities of Na+, K+ and Cl- were also investigated. The gradients were effectuated by mannitol. The initial relative rates of change of the intracellular activities of Na+ and Cl- were equal. The data were consistent with Na+ and Cl- ions initially remaining inside the cell and a cell membrane Lp of 10(-3) cm sec-1 osm-1, which is close to the values determined by Spring and co-workers (K.R. Spring, A. Hope & B.E. Persson, 1981. In: Water Transport Across Epithelia. Alfred Benzon Symposium 15. pp. 190-200. Munskgaard, Copenhagen). The initial rate of change of the intracellular activity of K+ was only 0.1-0.2 times the change observed in Na+ and Cl- activities, and suggests that K+ ions leave the cell during the osmotically induced H2O efflux and enter with an induced H2O influx. The coupling is between 98 and 102 mmoles liter-1. Various explanations for the anomalous behavior of intracellular K+ ions are considered. A discussion of the apparent coupling between K+ and H2O, observed in nonsteady states, and its effects on the distribution of K+ and H2O across the cell membrane in the steady states, is presented.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002712:Chlorides / Q000378:metabolism; D004848:Epithelium / Q000502:physiology; D005704:Gallbladder / Q000502:physiology*; D007700:Kinetics; D008839:Microelectrodes; D009092:Mucous Membrane / Q000502:physiology; D009337:Necturus; D009994:Osmolar Concentration; D010477:Perfusion; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium