title: Characterization of 42K+ and 86Rb+ transport and electrical membrane properties in exponentially growing neuroblastoma cells.
abstract: For measuring K+ efflux from exponentially growing neuroblastoma cells (clone Neuro-2A), two methods were used, a sampling method and a washing method. Both methods indicated that K+ efflux kinetics were as from a two-compartment system, but the two compartments could only be resolved completely using the washing method. A fast compartment, containing 143 +/- 16 nmol K+/10(6) cells, was found to be associated to the cell surface, and a slow compartment, containing 151 +/- 7 nmol K+/10(6) cells, was found to represent the intracellular K+. The rate constant of the slow compartment was 0.0164 +/-0.0005 min-1, and the K+ efflux rate was 2.46 +/- 0.14 nmol K+/10(6) cells per min. Using the appropriate conditions to measure K+ influx, the kinetics of influx were equal to the kinetics of efflux, indicating steady-state conditions. In addition a comparison was made between 42K+ and 86Rb+ as radioactive tracers for K+ flux. It was found that 86Rb+ was specifically bound on both the inside and the outside of the cells, and for this reason was not a suitable tracer for studying K+ flux kinetics in neuro-2A cells. A membrane potential of -42.9 +/- 1.3 mV and intracellular K+ activity of 108.1 +/- 3.0 mM were measured using conventional and ion-selective microelectrodes. A correlation was made between the K+ flux and electrophysiological data, using the equations of electrodiffusion theory. Thus, the permeabilities of K+ and Na+ were calculated as (3.9 +/- 0.4) . 10(-8) cm/s and (0.6 and 0.1) . 10(-8) cm/s respectively, together with K+ conductance of (2.8 +/- 0.3) . 10(-6) omega-1/cm2.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D051379:Mice; D009374:Neoplasms, Experimental / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D012413:Rubidium; D011188:Potassium