Summary
The relationship between the rate of Cl− transport and the electrical properties ofHalicystis parvula was investigated. Three metabolic inhibitors-darkness, cyanide (2mm), and low temperature (4°C)-all rapidly and reversibly reduce both the short circuit current (SCC), which is a measure of net Cl− transport, and the vacuole electrical potential (PD). Plotting thePD vs. SCC for inhibited cells yields a linear regression with ay-intercept of zero. ThePD is also greatly reduced when the [Cl−] of the external medium is lowered. Raising the external [K+] produces an appreciable, but less than Nernstian, depolarization, while increasing the external [H+] tenfold has no net effect on thePD. Decreasing the external [Na+] by tenfold produces only a slight depolarization. Thus, the outer plasma membrane appears to be moderately selective for K+ over Na+ or H+. The effects of ion substitutions in the vacuolar perfusing solutions on thePD reveal that the vacuolar membrane does not discriminate electrically between Cl− and the much larger anions, isethionate and benzenesulfonate, or between Na+ and K+. The data suggest that in internally perfused cells ofH. parvula generation of thePD of −50 to −60 mV by a transport system involving only electroneutral pumps is unlikely and that most of thisPD is generated by an electrogenic Cl− pump.
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Graves, J.S., Gutknecht, J. Chloride transport and the membrane potential in the marine alga,Halicystis parvula . J. Membrain Biol. 36, 65–81 (1977). https://doi.org/10.1007/BF01868144
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DOI: https://doi.org/10.1007/BF01868144