The secretory mechanism in adrenal chromaffin cells by nitrophenol compounds: possible involvement of the change in the surface potentials

The rabbit adrenal gland was perfused with a modified Locke's medium and the mechanism of adrenaline secretion induced by nitrophenol compound was investigated. The secretory response to 2,4-dinitrophenol (DNP) or trinitrophenol (TNP) showed the following peculiar features. (1) Prolonged exposure to DNP or TNP caused an immediate, and long-lasting increase of secretion only in the presence of Ca. (2) The response to DNP depended on the concentration of Ca, but that to TNP was largest in the presence of 0.5 mM Ca. (3) Re-addition of 2 mM Ca during prolonged exposure to DNP or TNP produced a larger response than did the simultaneous addition of Ca and either DNP or TNP. (4) The response to DNP in the presence of 2 mM Ca was markedly reduced by removal of external Na, but the Na dependency became less marked in the presence of 0.1 mM Ca. The response to TNP in the presence of 0.5 mM Ca was slightly reduced in the absence of Na. (5) DNP or TNP caused a much larger response during depolarization with a high K, Rb, or Cs medium than that with a 5 mM KCl medium. (6) The response to DNP was largely potentiated in the absence of most ions in the presence of only 0.1 mM Ca and that to TNP was potentiated in the presence of only 0.5 mM Ca under the same condition. (7) Re-addition of Ca 5 min after the removal DNP or TNP still caused substantial secretion. These results suggest that nitrophenol compounds stimulate secretion by two independent mechanisms: one is related to its effect on the surface potentials of the plasma membrane and the other unknown except for the possible dependence of Na and Ca.