Membrane potential measurement in cells of the adrenal gland.

1. Recordings of transmembrane potentials have been made in vitro from the cells of the adrenal gland using glass micro-electrodes.2. There was only a small species variation in the mean membrane potential of the cortical cells of the rabbit, rat and kitten; 66.2, 70.5, and 71.4 mV respectively.3. The membrane potential of cortical cells was dependent upon the external potassium concentration, [K](o). Raising [K](o) above the normal concentration of 4.7 mM by addition of KCl decreased the membrane potential; lowering [K](o) from normal increased it. The decrease in membrane potential was still evident when chloride was replaced by sulphate. Increasing [K](o) 10-fold decreased the membrane potential of rabbit cortical cells by 44 mV and of kitten cortical cells by 50 mV.4. The mean membrane potential measured in medullary chromaffin cells was for the rabbit 24.2 mV, rat 20 mV, and kitten 31.7 mV. The potentials of medullary cells were much less affected by changes in [K](o) than were cortical cell potentials.5. Age had little influence upon either cortical or medullary membrane potentials of adrenal glands, at least in early life.