MEMBRANE-POTENTIAL OF RAT HEPATOMA-CELLS IN CULTURE - INFLUENCE OF FACTORS AFFECTING AMINO-ACID-TRANSPORT

The effect has been studied of various media, hormones and of amino ac ids on the membrane potential of rat hepatoma cells in culture measure d by microelectrode impalement. Cells in Eagle's minimal essential med ium plus 5% serum had a value which varied daily from about 5-8 mV, in side negative. The membrane potential of rat hepatocytes was measured to be 8.7+/-0.2mV, inside negative. The membrane potential of the hepa toma cells was decreased by insulin and increased by glucagon. Membran e potential was unaffected by change of medium to Hanks' or Earle's ba lanced salt solutions or deprivation of serum. It was, however, reduce d in cells in phosphate-buffered saline and by reduction of pH. The fo rmer effect was shown to be due to the higher [Na+] of phosphate-buffe red saline as opposed to the other media. Addition of alanine, glycine , serine, proline and methylaminoisobutyrate all reduced membrane pote ntial by 2-3 mV. Smaller decreases were seen with methionine, leucine and phenylalanine, but none with glutamine, threonine, BCH (2-aminonor borane-2-carboxylic acid) and D-alanine. The results are compared with the effects of similar conditions on aminoisobutyrate uptake. Whilst there was a correlation under some conditions there was not under othe rs. It is concluded that for the hepatoma cells factors additional to the membrane potential must exert some influence on the capacity for a mino acid transport.