Increase in the resting potassium permeability of crayfish axons by pentachlorophenol and trinitrophenol in the absence of extracellular Ca 2+

Abstract

1. The possibility that the increase in the potassium permeability of resting neural membranes by phenol derivatives could be due to an increase in the influx of extracellular Ca 2+ ions was tested by experiments on crayfish giant axons. The Ca 2+ ions of the physiological solution were replaced with Ba 2+, Co 2+ or La 3+ ions (which are known not to activate calcium-dependent potassium channels), or with Na +. 2. In the absence of divalent or trivalent cations pentachlorophenol (PCP) and 2,4,6-trinitrophenol (TNP) did not increase the resting potassium permeability. 3. An increase in potassium permeability was caused by TNP but not by PCP in the presence of La 3+ and by both compounds in the presence of Co 2+. 4. The delay in the increase in potassium permeability brought about by the divalent-cation ionophore A23187 in the presence of Ca 2+ was longer than that related to the action of the phenols. A23187 had no effect in the presence of Co 2+. 5. It is concluded that calcium-dependent potassium channels are not involved in the increase of the resting potassium permeability of the axon membrane by phenol derivatives.