ISSN:
1615-6102
Keywords:
Intracellular Ca2+
;
Membrane excitation
;
Membrane potential
;
Membrane resistance
;
Nitellopsis
;
Tonoplast-free cell
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Internodal cells ofNitellopsis obtusa were made tonoplast-free by intracellular perfusion of the vacuole with medium containing 5 mM EGTA. Next, the cells were perfused with media of various Ca2+ concentrations and the plasma membrane potential (Em) and resistance (Rm) were measured by the open-vacuole method. In the presence of ATP, 10−7 M Ca2+ had no effect on Em and Rm but 10−6 M Ca2+ depolarized Em slightly and decreased Rm a little. Ca2+ at more than 10−5 M depolarized Em drastically (Em: about −10 to − 20 mV) and decreased Rm to almost zero. Even when the electrogenic pump was stopped by removing ATP, the Ca2+ effect was almost the same as that observed in its presence. The maximum depolarization level measured in the presence of more than 10−5 M Ca2+ was more positive than the peak of the action potential. Therefore, the intracellular concentration of Ca2+ ([Ca2+]i) should not become more than 10−5 M during excitation. The tonoplast-free cell did not release Cl− to the external medium during depolarization induced by high [Ca2+]i. Since no Cl− efflux was observed on membrane excitation in the tonoplast-free cell, the question remains of whether or not the depolarization accompanying excitation is caused by a transient increase in [Ca2+]i which was demonstrated byWilliamson andAshley (1982).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01284746
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