A study of the primary effect of the uncoupler carbonyl cyanide m-chlorophenylhydrazone on membrane potential and conductance in Riccia fluitans

Abstract

1. In the presence of 10(-5) to 10 (-8) M carbonyl cyanide m-chlorophenylhydrazone (CCCP) the membrane potential of thallus cells of the aquatic liverwort Riccia fluitans responds to changes of the external pH between 5.5 and 8.3. This occurs in the light and dark, and also if respiration is abolished by addition of 10(-4) M KCN and 10 (-5) M salicyl-hydroxamic acid. 2. The ATP-level of the thallus is reduced, independently of the external pH, by greter than or equal to 10 (-6) M CCCP to 30--40% of the control level of about 1.1 nmol ATP per mg dryweight within 5 min. 3. Upon addition of 10 (-4) M CCCP at 20 degrees C the ATP-level declines exponentially with a half time of about 20--30 s, whereas the membrane potential declines exponentially with a half time of about 2--3 s. 4. At pH 7.2 the electrical membrane conductance yields a sigmoid curve as a function of the logarithm of the CCCP concentration between 10 (-8) and 3 - 10 (-6) M. On the other hand, at 3 - 10(-7) M M CCCP the gm (electrical slope conductance, muS - cm-2 = 10 (-6)-omega-1-cm-2) versus pH-curve displays an optimum between pH 6.5 and 7.5. 5. We conclude that CCCP acts upon membrane potential and conductance in Riccia predominantly by inducing a passive proton permeability of the cell membrane, i.e. CCCP raises the permeability ratio, PH/PK, more than 100-fold above its control level of about 10.