The Membrane Potential of <i>Acetabularia mediterranea </i>

Saddler, Hugh

doi:10.1085/jgp.55.6.802

Cited by 99 publications

(36 citation statements)

References 28 publications

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“…The Valonia plasmalemma potential of about -70 mv found here is of similar magnitude to the value in other marine algae (12,15), with the exceptions of Nitellopsis obtusa, where it is -130 mv (21), and Acetabularia mediterranea, where it is -170 mv (26). The values of E,, in freshwater algae and in higher plants are usually somewhat higher than in Valonia and range from about -I10 to about -200 mv (18).…”

Section: Effects Of Concentration Changes Of Other Ions In Aswsupporting

confidence: 77%

Electrical Properties of the Plasmalemma and Tonoplast in Valonia ventricosa

Davis¹

1981

Plant Physiol.

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Studies were made on the electric potentials of the plasmalemma (Em.) and tonoplast (E,) in small cells (1-3 mm diameter) of Valonia ventricosa.To measure E,,,, microelectrodes with long tapers were inserted into the vacuole with the path of electrode entry off-center. The microelectrode then was pushed across the vacuole and into the cytoplasm on the opposite side of the cell. A reference electrode was placed in the artificial seawater bathing the cell. A similar method was used to measure E, except that the reference electrode was placed in the vacuole.Both E,, and E,,, were influenced by light. In the light, E¢o was -70 millivolts and it changed to -60 millivolts in the dark (cytoplasm-negative to outside). For E,,,, the potentials were +86 millivolts in the light and +69 millivolts in the dark (vacuole-positive to cytoplasm). The vacuole potential (E,.) was demonstrated to be the algebraic sum of E". and E,,,> For example, in the light, the sum of the means (±SE) for E>o (= -70 ± 1) and E,,, (= +86± ) is +16 millivolts, which is comparable to the measured E>o of +17 ± 2 millivolts. In the dark, the sum of E,. (= -60 ± 3) and E, (+69 ± 6) is +9 millivolts and the measured value of E"o is +9 ± 4 millivolts.The external K+ concentration had a controlling effect on both E". and the direct current resistance of the plasmalemma, which suggests that E,.. is largely a K+ diffusion potential. The tonoplast electrical properties were affected only slightly by external K+.The data presented are indicative of a K+ electrogenic influx pump in the tonoplast. It is also considered possible that H+ might be electrogenically pumped from the cytoplasm both into the vacuole and to the cell exterior.In 1924, Osterhout (25)

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Section: Effects Of Concentration Changes Of Other Ions In Aswsupporting

confidence: 77%

Electrical Properties of the Plasmalemma and Tonoplast in Valonia ventricosa

Davis¹

1981

Plant Physiol.

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“…The CI-pump in AcetabuIaria is strongly electrogenic and produces about -80 mV of the -170 mV PD, the remaining -90 mV being produced by a predominantly K § diffusion potential (Saddler, 1970;Gradmann, 1970). The pump-generated PD of -55mV in internally perfused H. parvula is superimposed on a diffusion potential of 0 mV, and this accounts for the difference in total PD, which is the most conspicuous difference between the electrical properties of these two organisms.…”

Section: Comparisons With Acetabulariamentioning

confidence: 99%

Current-voltage relationships and voltage sensitivity of the Cl− pump inHalicystis parvula

Graves

Gutknecht

1977

J. Membrain Biol.

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Summary. The current-voltage (I-V) relationships for internally perfused and nonperfused cells of Halieystis parvula were determined. In both types of cells the I-V curve shows a conspicuous region of negative slope, beginning at vacuole potentials around -30 mV and continuing to values of +20 to + 40inV. The negative slope in perfused cells is abolished by the metabolic inhibitors, darkness and low temperature. In order to determine the origin of this negative slope, we measured the voltage sensitivity of the unidirectional fluxes of CI-, Na + and K + in perfused cells. The results show that the C1-influx, which is mediated primarily by a C1-pump, increases as the vacuole potential is clamped at increasingly more negative values up to -50mV, while the other fluxes measured changed in the directions predicted by the change in electrical driving force. The voltage sensitivity of the C1-pump quantitatively accounts for the negative slope of the I-V curve. Also, we observed a large transient outward current of 10-20-sec duration following an abrupt depolarization by voltage clamping. This transient current was reduced or abolished by low temperature, which suggests that it may be due to the voltage-sensitive C1-pump. Finally, we found an inverse relationship between the transprotoplasm resistance (Rm) and the PD under standard conditions, which suggests that the activity of the electrogenic C1-pump lowers Rm, i.e., it is a conductive pump.An electrogenic pump is an active transport system which transports net ionic current and thus generates an electrical potential difference (PD) across a membrane. In separate theoretical models Finkelstein (1964) and Rapoport (1970) proposed that an electrogenic pump may be voltage sensitive and consequently contribute to the membrane conductance. There is experimental evidence for the existence of voltagesensitive, electrogenic pumps in the marine alga, Acetabularia (Gradmann, 1975), the freshwater alga, Nitella (Spanswick, 1972), a molluscan nerve (Kostyuk, Krishtal & Pidoplichko, 1972) & Curran, 1973). In the frog skin direct flux measurements have been made to support this hypothesis, but the direction of voltage sensitivity and the anatomical complexity of the skin make the interpretation equivocal.In the marine alga, Halicystis parvula, the inwardly directed C1-pump appears to be strongly electrogenic, accounting for nearly all of the -50 to -60 mV potential difference (PD) in internally perfused cells (Graves & Gutknecht, 1977). When connected to a voltage clamp device, the perfused cells of H. parvula allow the investigation of both the current-voltage relationships and the voltage dependence of the unidirectional fluxes of various ions. The existence of a negative slope region in the I-V curve of H. parvula suggested that the electrogenic C1-pump might be voltage sensitive, and we have investigated this possibility with direct determination of the voltage-dependent changes in direction and magnitude of the fluxes of CI-, Na + and K +. In addition, the effects of metab...

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“…Saddler (1970) has shown that a PD of similar magnitude (i.e., -70 to -80 mV) is generated by an electrogenic CI-pump in Acetabularia mediterranea. While electrogenic pumps appear to play an appreciable role in generating the PD in several other plant cells, the ion(s) which is transported electrogenically is usually not known (Higinbotham, 1973).…”

Section: Relationship Between Pd and Sccmentioning

confidence: 99%

Chloride transport and the membrane potential in the marine alga,Halicystis parvula

Graves

Gutknecht

1977

J. Membrain Biol.

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Summary.The relationship between the rate of C1-transport and the electrical properties of Halicystis parvula was investigated. Three metabolic inhibitors-darkness, cyanide (2 raM), and low temperature (4 ~ -all rapidly and reversibly reduce both the short circuit current (SCC), which is a measure of net C1-transport, and the vacuole electrical potential (PD). Plotting the PD vs. SCC for inhibited cells yields a linear regression with a yintercept of zero. The PD is also greatly reduced when the [C1-] 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 the PD. 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 the PD reveal that the vacuolar membrane does "not discriminate electrically between C1-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 the PD of -50 to -60 mV by a transport system involving only electroneutral pumps is unlikely and that most of this PD is generated by an electrogenic C1-pump.An unusual feature of the giant-celled marine alga, Halicystis parvula, is that the Na +, K + and C1-concentrations in the vacuolar sap are similar to those in the seawater in which the cell is growing (Graves & Gutknecht, 1976). The electrical potential difference (PD) between the vacuole and external solution is -82 mV (inside negative) in nonperfused cells. This PD cannot be generated by any combination of diffusion potentials for these ions between the vacuole and external medium, because each of these ions has an equilibrium potential near zero. Thus the origin of the PD in H. parvula presents an intriguing question.In their early investigations on the bioelectric properties of Halicystis, Blinks and co-workers made several interesting observations which were

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The Membrane Potential of Acetabularia mediterranea

Cited by 99 publications

References 28 publications

Electrical Properties of the Plasmalemma and Tonoplast in Valonia ventricosa

Electrical Properties of the Plasmalemma and Tonoplast in Valonia ventricosa

Current-voltage relationships and voltage sensitivity of the Cl− pump inHalicystis parvula

Chloride transport and the membrane potential in the marine alga,Halicystis parvula

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