Effects of furosemide on the resting membrane potentials and the transmitter-induced responses of the Aplysia ganglion cells.

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Abstract
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 or conductance. Na+-dependent responses to acetylcholine (ACh) were slightly depressed but Cl--dependent responses to ACh and .gamma.-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--channel activities, the greater effect on the open Cl--channels. In addition, its 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.