Calcium Concentration In Medium Research Articles

Calcium Uptake by Calcicole and Calcifuge Species in the Genus Agrostis L.

The description 'low mineral requirement' has often been applied to a species which has been found to grow satisfactorily on a medium with low concentrations of certain nutrients, upon which another species shows poor growth. While it may be correct to assume that the first species has a lower mineral requirement, the possibility also exists that it is able to exploit the resources of the medium more efficiently, thus satisfying similar requirements from a more restricted source of supply. If, in studies of this type, uptake of nutrients by the plant is considered in conjunction with data on growth responses it may be possible to determine whether one or both of these factors is in operation. The growth responses of calcicole and calcifuge plants to the calcium concentration in the external medium have been shown to differ in experimental studies by Olsen (1942), Bradshaw, Lodge, Jowett & Chadwick (1958) and Jefferies & Willis (1964). Direct comparisons are most easily interpreted where closely related species have been examined. In recent publications by Bradshaw et al. (1958), Snaydon & Bradshaw (1961) and Clymo (1962), related calcicole and calcifuge species were shown to respond to calcium levels in a manner which was closely correlated with the calcium status of the soil in which they normally grew. Olsen (1942), Snaydon & Bradshaw (1961) and Jefferies & Willis (1964) are amongst the few workers who have considered data on both calcium uptake and growth responses when arriving at conclusions concerning the calcium requirements of the species they examined. In sand culture experiments Bradshaw et al. (1958) determined the optimum calcium concentrations for the growth of Agrostis canina, A. stolonifera and A. tenuis. These levels were closely related to the calcium status of the soils in which the species are distributed. In the present work a comparison has been made of the calcium uptake and the growth responses of A. canina, A. setacea, A. stolonifera and A. tenuis to various calcium concentrations. Particular attention has been given to determining whether the wellmarked calcifuge species, A. setacea, grows satisfactorily with low internal concentrations of calcium or whether it is able to take up calcium from soil and water cultures more efficiently than the more mesic and calcicole members of the genus.

A study of the crustacean axon repetitive response. II. The effect of cations, sodium, calcium (magnesium), potassium and hydrogen (pH) in the external medium.

AbstractThe effects of sodium, calcium, potassium (magnesium), potassium, and hydrogen (pH) ion concentration in the external medium on the repetitive response and the transmembrane electrical parameters of the crustacean axon have been investigated. (1) The action potential is reduced with decrease in sodium ion concentration, the relationship is linear if the spike voltage is plotted against the log (Na0). The action potential amplitude does not increase significantly, above 135 mv, attained at Na0 = 452 mM, if Na0 is increased. (2) The repetitive response and oscillatory activity in general disappears as the sodium concentration is reduced to less than 150 mM. (3) The critical firing level increases with decrease in sodium, the relationship linear with respect to log (Nao). (4) The positive after potential amplitude is not affected by the sodium concentration. (5) The membrane resistance is not affected by sodium concentration. (6) Calcium lack results in decreased critical firing level and spontaneous firing, followed by a total and irreversible loss of excitability. The membrane resistance is markedly decreased. Polarizing current, if applied early after the onset of the calcium lack effect, may restore, at least partially, the excitability phenomenon. (7) Calcium excess increases membrane resistance, depresses excitability. Calcium concentration of 150 mM abolishes the repetitive response. (8) There is a 3.3+: 1 ratio Na:Ca for threshold level of repetitive response. Lower ratio figures, by reducing Na or increasing Ca or both, eliminates repetition. Increasing the ratio figure by increasing sodium or decreasing calcium or both augments oscillatory activity. This ratio is constant between the limits 400 mM Na:125, Ca to 90 mM Na:25 mM Ca. (9) Magnesium may substitute for calcium, the Na:Mg ratio for repetitive response threshold is 3.3:2. (10) Repetitive firing may be elicited over a wide range of pH values 4.2–10.5; membrane potential and resistance values decline invariably at pH values above 9.5 and below 4.5. (11) Repetitive firing is enhanced by increasing pH values, depressed by reducing pH values. (12) Effect of excess potassium produces depolarization, reduced membrane resistance, inactivation and abolition of repetitive firing, may be relieved by applied hyperpolarization. (13) Potassium lack results in membrane potential and resistance irreversible decline, permanent inactivation, total loss of excitability. Partial restoration by strong hyperpolarization if applied before effect is complete. Potassium replacement in solution only slows or temporarily arrests the overall membrane deterioration. (14) Conclusions ‐ sodium controls spike, potassium controls after potential, calcium (magnesium) controls membrane permeability, pH controls amount of available ionized calcium. Repetitive firing requires proper ratio 3.3/1 of (Nao)/(Ca0), pH above 7.6 and potassium at 15 mM in solution.

On the integrative synaptic potentials of Onchidium nerve cell.

1. Excitatory postsynaptic potentials (e. p.s. p.'s) of the giant nerve cell system of Onchidium verruculatum were investigated by intracellular electrode technique.2. An impulse of a single presynaptic fibre was usually too small to initiate a postsynaptic spike and spacial and temporal summation was necessary to produce the postsynaptic spike.3. The increase of calcium or magnesium concentration in the external medium increased or decreased the amplitude of the e. p.s. p.respectively but the maximum amplitude of the synaptic potential reached by repetitive presynaptic stimulation was practically unchanged.4. From the above results the temporal facilitation is produced by increasing the active area of the synaptic membrane innervated by a single presynaptic fibre.