The electrophysiological properties of the membrane ofNicotiana tabacumvar. Sarnsun cultured cells were determined using a microelectrode technique in standard medium containing 1 mMKC1, 1 mMNaCl and 1 mu CaCl2at pH 7. Tobacco callus was derived from the pith (Em=−104.416.2 mV). The membrane potentials of the callus cells did not show a symmetrical Gaussian distribution but were scattered over a wide range. The percentage of high membrane potential cells increased as the subculture was continued until about 11 months and then decreased. The response of the membrane potential to electric stimulus, ionic composition, metabolic inhibitors, sugars and amino acids was characteristic of high (Em=−˜−160 220 mV; H-cells) and low (Em=−80˜−90 mV; L-cells) membrane potential cells. The membrane potential of H-cells was largely depolarized by addition of CN−, carbonium cyanidem-chlorophenylhydrazone, decyclohexylcarbodiimide, and triphenyltin chloride and transiently depolarized by addition of glucose, galactose, mannose or sucrose, and D-alanine, L-alanine or Llysine, but the membrane potential of L-
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