ISSN:
1432-2048
Keywords:
ATP
;
Electrogenic ion pump
;
Membrane excitability
;
Membrane potential
;
Nitellopsis
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The membrane potential of tonoplast-free cells of Nitellopsis obtusa Graves in relation to the intracellulcar concentration of ATP ([ATP])i was measured using either the ordinary microelectrode method or the open-vacuole method (M. Tazawa, M. Kikuyama and S. Nakagawa, 1975, Plant Cell Physiol. 16, 611). The intracellular ATP concentration was modified in the microelectrode method by introducing into the cell ATP-regenerating media composed of phosphoenolpyruvate and pyruvate kinase, and in the open-vacuole method by continuously perfusing the cell interior with media of known ATP concentrations. Plots of the membrane potential against the [ATP]i follow a rectangular hyperbola. Using the microelectrode method, the maximum ATP-dependent potential was about-120–130 mV and the apparent K m about 10–30 μM. When the openvacuole method was used, the maximum ATP-dependent potential was about 100 mV and the apparent K m about 100 μM. The membrane was still excitable when the [ATP]i was 10 μM but not at 1.7 μM [ATP]i. The membrane resistance increased in parallel with a decrease in [ATP]i or membrane depolarization, but decreased again at a very low [ATP]i (1.7 μM).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00393642
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