Effects of Furosemide on the Resting Membrane Potentials and the Transmitter-Induced Responses of the Aplysia Ganglion Cells

Effects of Furosemide (FM) on the ionic channels in the ganglion cells of Aplysia were investigated using a conventional electrophysiological method. Application of 1 mM FM for 30 min did not alter the resting membrane potential ox conductance. Na⁺-dependent responses to acetylcholine (ACh) were slightly depressed but Cl^--dependent responses to ACh and γ-aminobutyric acid (GABA) were markedly depressed by FM. On the other hand, K⁺-dependent responses to ACh and dopamine (DA), and cyclic adenosine-3′, 5′ monophosphate (cAMP)-dependent response to DA were not appreciably altered by 1 mM FM. The depressing effects of FM on both Na⁺-and Cl^--dependent responses were due to the non-competitive inhibition of their receptor activities. It was concluded that 1 mM FM can change neither Na⁺-K⁺-pump nor Cl^--pump mechanisms in the ganglion cells of Aplysia, but it depresses the receptor-operated Na⁺-and Cl^--ehannel activities, the greater effect on the open Cl^--channels. In addition, it was postulated that FM effect may be highly specific to the open state of Cl^--channels regardless of whether the membrane is excitable or not.