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J Dainty

Publications and source records attributed to J Dainty.

9 recordsLinked to original sources
PubMed1992

Cytoplasmic chloride regulates cation channels in the vacuolar membrane of plant cells.

This study is concerned with the characterization of the ionic currents in the vacuolar membrane (tonoplast) of plant cells. Voltage patch-clamp experiments at the whole vacuole and single channel levels were employed to study the effects of cytoplasmic chloride on the tonoplast inward rectifying currents of sugar beet cultured cells. Whole vacuole experiments showed that removal of cytoplasmic chloride induced a decrease in the level of the inward currents, an effect that was reversed upon returning to control levels of cytoplasmic chloride. Substitution of cytoplasmic chloride by any other anion (organic or inorganic) resulted in a reduction in the level of the inward currents. At a given negative tonoplast potential, the inward currents showed a linear relationship with the concentration of cytoplasmic chloride between 10 and 100 mM, with the slope of these relationships increasing as the potential was made more negative. Single channel experiments showed that reduction of cytoplasmic chloride changed the gating mechanism of the channels without affecting the single channel conductance. Reduction of cytoplasmic chloride caused a decrease in the open probability of the tonoplast cation channels by reducing their mean open time and by inducing the appearance of an additional closed state.

Cells, Cultured↗
PubMed1984

Electrophysiology of a clonal osteoblast-like cell line: evidence for the existence of a Ca2+-activated K+ conductance.

Intracellular microelectrode measurements were made on a well-characterized osteoblast-like clonal cell line isolated from a rat osteosarcoma. In serum-free medium, stable membrane potentials of -42 +/- 9 mV (SD, n = 190) were recorded. Ion substitution experiments suggested that this membrane potential is primarily a Na+/K+ diffusion potential. Input resistance was correlated strongly with colony size, ranging from 49 +/- 18 M omega (SD, n = 14) for colonies of 1-3 cells, to 4 +/- 4 M omega (SD, n = 164) for colonies of 100 or more cells. These results are consistent with the existence of low resistance intercellular junctions. Application of the carboxylic calcium ionophore A23187 by pressure microejection onto the cell surface resulted in a transient hyperpolarization and concomitant decrease in input resistance. Both these effects are consistent with an increased K+ conductance. Ion substitution experiments demonstrated that the degree of hyperpolarization was dependent on the external concentration of both K+ and Ca2+. Quinine, a blocker of Ca2+-activated K+ channels, inhibited the ionophore-induced hyperpolarization in a dose-dependent manner. It was concluded that these cells exhibit a Ca2+-activated K+ conductance.

Animals↗
PubMed1977

Plasmalemma transport of OH- in Chara corallina: dynamics of activation and deactivation.

The light-mediated, time-dependent rise in the pH value at the center of an alkaline band was analyzed using the methods of numerical analysis. From this analysis an expression of the time-dependent build-up of OH- efflux was obtained for these bands. This information can now be employed to determine whether the light-activated transport of OH- and HCO3- influences the electrical properties of the plasmalemma. The dark-induced deactivation of OH- transport was also characterized, revealing a transition from efflux to a transient influx phase during deactivation. Numerical analysis of the steady-state OH- diffusion pattern, established along the surface of an alkaline band, revealed that the OH- efflux width was wider than previously envisaged. It was also found the OH- sink regions exist on either side of the efflux zone. These, and other characteristics revealed by the numerical analysis, enabled us to extend the OH- transport model proposed by Lucas (J. Exp. Bot. 1975, 26:347).

Biological Transport, Active↗
PubMed1966

Unstirred layers in frog skin.

1. Estimates of the magnitudes of the unstirred regions associated with isolated frog skin in sulphate Ringer's solution have been made under different stirring conditions.2. The method of investigation was an analysis of the time course of the p.d. transients which occurred when external sodium concentration and internal potassium concentration changes were made in the bathing solution.3. Making an arbitrary but reasonable assumption about the diffusional coefficient of Na(2)SO(4) in the outer unstirred region, the magnitudes of the outer unstirred layers were found to lie within the ranges 40-60 mu, 30-50 mu and 30-40 mu under stirring conditions of 120, 300 and 500 rev/min, respectively.4. Making an arbitrary but reasonable assumption about the diffusion coefficient of K(2)SO(4) in the inner unstirred region, the magnitudes of the inner unstirred layers were found to lie within the ranges 150-230 mu, 120-200 mu and 100-170 mu under stirring conditions of 120, 300 and 500 rev/min, respectively.

Animals↗
PubMed1966

An examination of the evidence for membrane pores in frog skin.

1. Measurements of the diffusional permeability, P(d), of tritiated water in isolated frog skin bathed in sulphate Ringer have been made under different stirring conditions.2. The mean +/- S.E. values for P(d) were found to be (6.5 +/- 0.3), (7.9 +/- 0.5), (9.7 +/- 0.7) and (11.1 +/- 0.8) x 10(-5) cm sec(-1) at 120, 300, 500 and 1000 rev/min. It is considered that these results indicate the existence of ;unstirred layers' associated with frog skin.3. The hydraulic conductivity, L(p), of the skin in sulphate Ringer was found to be (2.36 +/- 0.07) x 10(-7) cm sec(-1) atm(-1) (+/- S.E. of estimate), and no marked increase in this value for L(p) was found when the stirring rate was increased from 0 to 500 rev/min.4. It is considered that these results show that previous comparisons of the relative magnitudes of L(p)RT/V(w) (where V(w) is the partial molar volume of water) and P(d) for frog skin have been in error because of the presence of ;unstirred layers'.5. The bearing of our results and other evidence on the question of pores in cell membranes has been discussed.

Animals↗
PubMed1965

Osmotic flow.

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Chemical Phenomena↗