Significance of 2,4-dinitrophenol action on spinal motoneurones.

1. Extracellular iontophoretic applications of DNP lead to an increase in the membrane conductance of cat spinal motoneurones, manifested by a rise in input conductance, a slower rate of rise and fall of action potentials, and occlusion of the afterhyperpolarization. 2. There is also some hyperpolarization, but the reversal potential for the action of DNP is only about 12 mV more negative than the resting potential. 3. These effect of DNP can be abolished or significantly reduced by intracellular injections of EGTA. On the other hand, DNP can partly reverse the decreased conductance and the depression of the slow afterhyperpolarization caused by EGTA. 4. Intracellular injections of DNP also induce a rise in input conductance; when repeated, they tend to have a depolarizing effect, mainly irreversible. 5. It is concluded that DNP acts principally inside the motoneurone, by liberating bound internal Ca, the free Ca ions then raising membrane conductance, especially GK.