Changes in membrane potential induced by local anesthetic bupivacaine on mitochondria within Ehrlich ascites tumor cells

The effect of the local anesthetic bupivacaine on transmembrane potential of mitochondria within Ehrlich ascites tumor cells has been investigated by the safranine method. The following summarizes the results. 1) When Ehrlich ascites tumor cells were added into a medium containing safranine, a differential spectrum with a decrease at 520 nm appeared. The addition of bupivacaine did not reverse the response but resulted in a spectrum similar to that observed with deenergized mitochondria, with a maximum at 550 nm and a minimum at 495 nm. 2) The addition of glucose to bupivacaine- or rotenone-treated cells also produced a shift in safranine spectrum similar to that observed upon energization of mitochondrial membranes by ATP, thus suggesting that glycolytically generated ATP was responsible for this spectral change. 3) The ability of bupivacaine to decrease the membrane potential in mitochondria within Ehrlich ascites tumor cells was due to two different effects: inhibition of the energy-conserving site I of the respiratory chain and uncoupling by a true protonophoretic mechanisma.