Selective action of piretanide on primary afferent GABA responses in the frog spinal cord

The effects of piretanide, a drug which blocks active chloride transport in other systems, was examined on amino acid responses and synaptic potentials in the frog spinal cord. It was found that piretanide had no effect on GABA ventral root hyperpolarizing responses, but abolished dorsal root depolarizing responses. Dorsal root glutamate responses were little affected by piretanide. The depression of GABA responses on dorsal root ganglion cells was accompanied by a large decrease in the conductance change elicited by GABA. In addition, there was a small shift of the GABA equilibrium potential toward the resting membrane potential, which is consistent with a reduced inward pumping of chloride ions. Piretanide abolished the dorsal root potential elicited by ventral root stimulation. In addition it reduced the early part of the dorsal root potential evoked by stimulating an adjacent dorsal root but had remarkably little effect on the late phase.