Potassium transport in Neurospora

• 1.

  1. Wild-type Neurospora crassa, growing logarithmically in minimal medium, contains 180 ± 16 mM intracellular K⁺ and 14 ± 2 mM Na⁺. It requires K⁺ but not Na⁺ for growth. Over a wide range of extracellular K⁺ concentrations (0.3 to 100 mM), the cells maintain a constant, high level of intracellular K⁺ (180 mM) and rapid growth occurs. Below 0.3 mM, the internal K⁺ concentration falls and growth is inhibited.

• 2.

  2. When cells are harvested from logarithmic growth and resuspended in distilled water or in 1 mM sodium azide, they show no significant loss of internal K⁺ for at least 1 h. Exposure to the polyene antibiotic nystatin (30 μg/ml) or the decapeptide antibiotic tyrocidine (20 μg/ml) causes most of the internal K⁺ to be lost within 2 min. Both antibiotics are thought to attack the plasma membrane of sensitive organisms.

• 3.

  3. Neurospora exchanges its intracellular K⁺ quite rapidly for extracellular K⁺ or Rb⁺, but only slowly for Na⁺.

• 4.

  4. These experiments were undertaken to provide a backgroun for microelectrode studies with Neurospora and for the isolation of a K⁺-transport mutant.