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Physical Therapy Modalities/education , Congresses as Topic , Exercise Therapy , Physical Therapy Modalities , SportsABSTRACT
The presence of tonoplast ion channels regulated by voltage in the physiological range of transtonoplast electric potential was studied in isolated vacuoles from Acer pseudoplatanus cultured cells. In symmetrical KCl or K-gluconate depolarizing pulses induced instantaneously developing, decaying outward currents, while in symmetrical tetramethylammonium chloride these currents were absent. The outward currents were reduced if the depolarizations were applied from a holding potential of +30 millivolts and increased upon depolarizations from a holding potential of -30 millivolts and even more from a holding potential of -50 millivolts. These results indicate that the outward currents are due to K(+) movement through channels which are open around 0 millivolt and close at positive potentials. These K(+) channels, regulated in the range of the physiological electric potentials reported for the vacuoles in situ, are likely the same K(+) channels activated by hyperpolarizations which we have previously described (R Colombo, R Cerana, P Lado, A Peres [1988] J Membr Biol 103: 227-236).
ABSTRACT
The mechanism of the stimulating effect of lipophilic cations on H(+) extrusion in maize root segments (Zea mays L.) has been investigated. The measurement of the uptake of [(3)H]tributylbenzylammonium ([(3)H]TBBA(+)), the most active lipophilic cation on H(+) extrusion, indicated that although a relevant fraction of TBBA(+) taken up by the tissue is adsorbed to cell surfaces, a fraction of the cation enters the cells. However no correlation was observed between the rate of TBBA(+) uptake and that of H(+) extrusion. On the other hand, the lipophilic cations active on H(+) extrusion (TBBA(+) and dibenzyldimethylammonium (DDA(+))), in the presence of fusicoccin (FC), induced under the same conditions an efflux of Cl(-), while tetramethylammonium (TMA(+)), inactive on H(+) extrusion, did not. The stimulation of Cl(-) efflux by TBBA(+) was independent of the anion present in the medium and was inhibited by Na-orthovanadate, an inhibitor of plasma membrane ATPase and of TBBA(+)-induced H(+) extrusion. These results suggest that the stimulation of H(+) extrusion by TBBA(+) depends on its effect on Cl(-) efflux rather than on its penetration into the cells.
ABSTRACT
Auxin and fusicoccin (FC) stimulate the active uptake of 3-O-methyl glucose (3-O-MG) in those materials in which they have been shown to activate an electrogenic proton extrusion (Pisum sativum L. stems, Zea mays L. coleoptiles and roots). In maize roots the curve relating 3-O-MG influx to external concentrations indicated that the values of the apparent Km increase in the 3-O-MG concentration range between 2×10(-5) mol l(-1) and 2×10(-2) mol l(-1). FC did not alter the Km values and its stimulating effect was nearly constant at all 3-O-MG concentrations tested. Basal and FC-induced uptake of 3-O-MG appeared associated with a transient proton influx suggesting that also in maize roots a sugar-proton contransport occurs. Diethyl stilbestrol, which inhibits proton extrusion, inhibited also basal and FC-induced 3-O-MG uptake. The data support the view that the stimulation by FC of 3-O-MG uptake is closely related to that of proton extrusion. The stimulation by FC of 3-O-MG uptake cannot be replaced by increasing extracellular proton concentration, nor may be explained only by the FC-induced hyperpolarization of transmembrane potential difference. The hypothesis is proposed that the effect of FC on 3-O-MG uptake depends on an increase of cytoplasmic pH, following the activation of the proton extruding system.
ABSTRACT
Analogies and differences between the growth-promoting action of fusicoccin (FC), the toxic agent produced by Fusicoccum amygdali, and of indole-3-acetic acid (IAA) in etiolated pea internode segments were further investigated. It was confirmed that the effect of FC, at optimal concentration, on growth by cell enlargement is markedly higher (ca. 70%) than that of IAA. The lack of an inhibitory effect of FC at high concentrations corresponds to a lack of capacity of the toxin to induce ethylene synthesis. When FC and IAA are present together at suboptimal concentrations, the effects of the two substances are clearly additive. Growth stimulation by a mixture of FC and IAA at optimal concentrations is equal to that by FC alone. NaF, 2,4-DNP, actinomycin D, and cycloheximide strongly depress FC-induced stimulation of cell enlargement. These data are in agreement with the hypothesis that FC promotes growth through some effect on cell-wall extensibility probably identical to the one mediating auxin-induced growth, while the primary site of action of FC is different from that of the natural and synthetic auxins.
