Role Of Ca Ions Research Articles

The role of Ca ions in changes induced by excess Cu2+ in bean plants. Growth parameters

The effect of Ca on Cu toxicity in runner bean plants (Phaseolus coccineus L. cv. Piěkny Jaś) grown hydroponically in nutrient solution was studied. The toxic effect of excess Cu on plants depends on their age and Ca content in the medium. Copper applied in excess to the plants at the early phase of leaf development strongly limits the uptake of Ca ions from the nutrient solution, particularly their translocation to leaves. Increased Ca content limits the inhibitory effect of Cu on leaf growth and decreases the content of chloroplast pigments to the level approximate to that of control. At this growth stage the effect of excess Cu is at least partially connected with limited Ca transport to leaves. At the intermediate leaf phase Cu-treated plants react slightly to changed Ca content. At the end of the primary leaf development increased Ca concentration in the medium intensifies senescence processes induced by excess Cu. The changes are partially connected with intensified water deficit. Increased Ca content in the nutrient solution limits Cu accumulation in the individual organs of Cu-treated plants. However, Cu accumulation in leaves is not decreased at a high level of Ca. Copper generally decreases Ca content in the youngest plants, whereas in the oldest ones only in the case of a low level of Ca in the nutrient solution.

Possible role of Ca ions in the vestibular system.

The Ca++ messenger system is nearly universally present in the control of cell functions by extracellular messengers. It elicits different kinds of responses: either brief, as in neurotransmission and in skeletal muscle contraction, or sustained, as in smooth muscle contraction and in the regulation of transepithelial transport systems. In this latter function the Ca++ messenger system interacts with other cellular modulation systems such as cAMP production and arachidonic acid cascade. In the vestibular apparatus, the Ca++ messenger system is involved in the transduction processes in that it controls both the release of neurotransmitter at the basal pole of the hair cell and the electrical resonance of the cell. It also figures in the contractile properties of cochlear outer hair cells. The Ca++ messenger system as well as adenylate cyclase and prostaglandins may play an important role in the modulation of endolymph secretion.

Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.

The possible role of Ca ions in mediating the drop in sensitivity associated with light adaptation in Limulus ventral photoreceptors was assessed by simultaneously measuring the sensitivity to light and the intracellular free Ca concentration (Cai); the latter was measured by using Ca-selective microelectrodes. In dark-adapted photoreceptors, the mean resting Cai was 3.5 +/- 2.5 microM SD (n = 31). No correlation was found between resting Cai and absolute sensitivity from cell to cell. Typically, photoreceptors are not uniformly sensitive to light; the Cai rise evoked by uniform illumination was 20-40 times larger and faster in the most sensitive region of the cell (the rhabdomeral lobe) than it was away from it. In response to a brief flash, the Cai rise was barely detectable when 10(2) photons were absorbed, and it was saturated when approximately 10(5) photons were absorbed. During maintained illumination, starting near the threshold of light adaptation, steady Cai increases were associated with steady desensitizations over several log units of light intensity: a 100-fold desensitization was associated with a 2.5-fold increase in Cai. After a bright flash, sensitivity and Cai recovered with different time courses: the cell was still desensitized by approximately 0.5 log units when Cai had already recovered to the prestimulus level, which suggests that under those conditions Cai is not the rate-limiting step of dark adaptation. Ionophoretic injection of EGTA markedly decreased the light-induced Cai rise and increased the time to peak of the light response, but did not alter the resting Cai, which suggests that the time to peak is affected by a change in the capacity to bind Ca2+ and not by resting Cai. Lowering the extracellular Ca2+ concentration (Cao) first decreased Cai and increased sensitivity. Longer exposure to low Cao resulted in a further decrease of Cai but decreased rather than increased sensitivity, which suggests that under certain conditions it is possible to uncouple Cai and sensitivity.

Role of Calcium and Calmodulin in Plant Growth and Development

Abstract The role of Ca as an intracellular messenger is beginning to be unraveled as a result of recent research on calmodulin, a ubiquitous protein that binds Ca ions and regulates various biochemical processes in plants. Experimental evidence suggests that certain cell functions in plants are regulated, in part, by Ca and calmodulin. Changes in cell wall rigidity, membrane permeability, and enzyme activation are known to influence various aspects of cell physiology and have a significant influence on the growth and development of plants. Deficiency of Ca is known to induce physiological disorders in fruit and vegetables. We hope that this article will stimulate further studies and provide new insights into how these problems may be controlled. The role of Ca ions in signal transduction and cell function is beginning to be understood at the molecular level, and we have embarked on a new phase of the old subject of mineral nutrition, especially as it applies to Ca and plant growth and development.

The role of Ca ions and cAMP in ACTH lipolysis

Ca ions and cAMP are known to be involved in the action of hormones. In this study, the actions of Ca ions and cAMP in ACTH lipolysis were investigated by comparing ACTH1-24, ACTH1-10 and ACTH11-24 with regard to: lipolytic activity, binding affinity to the fat cell membrane, changes in Ca ion binding to the fat cell membrane and cAMP formation. Rat adipocytes were used. Lipolytic activity was measured in terms of the amount of FFA released from fat cells into the medium after incubation with the ACTH analogs at 37 degrees C for 30 minutes. Binding affinity to the fat cell membrane was expressed as competitive binding affinity, determined by simultaneously incubating fat cell ghosts with 125I-ACTH1-24 and unlabelled ACTH analogs at 4 degrees for 40 minutes. Changes in Ca ion binding to the fat cell membrane was expressed as Ca binding capacity, measured by simultaneously incubating fat cell ghosts with 45Ca and ACTH analogs at 24 degrees C for 20 minutes. CAMP formation was measured by RIA as the amount of cAMP formed in fat cells incubated with 10(-6)M ACTH analogs at 37 degrees C for 0, 3, 5 and 10 minutes. FFA release after incubation with each of the ACTH analogs at 10(-6) M was 1.17 mEq/L/tube for ACTH1-24, 0.26 mEq/L/tube for ACTH1-10 and 0.25 mEq/L/tube for ACTH11-24, showing a high value only for ACTH1-24. The binding affinity to the fat cell membrane (high affinity constant) was 4.4 X 10(-8) M for ACTH1-24, 4.6 X 10(-8) M for ACTH1-10 and 4.6 X 10(-8) M for ACTH11-24. There were no significant differences among the binding affinities of these ACTH analogs. The binding capacity of 45Ca++ to the fat cell membrane (high affinity constant) was 3.64 X 10(-6) M for ACTH1-24, 4.49 X 10(-6) M for ACTH1-10 and 5.46 X 10(-6) M for ACTH11-24. There were no significant differences among these ACTH analogs. The increase in cAMP formation during the first 3 minutes of incubation was 35.5 fmol/mg dry weight of fat cells for ACTH1-24, 2.2 fmol/mg for ACTH1-10 and 1.8 fmol/mg for ACTH11-24. An increase was only observed for ACTH1-24. The fact that FFA release and cAMP formation were high only with ACTH1-24 among the ACTH analogs tested indicates that cAMP formation plays an important role in the lipolytic activity of ACTH in fat cells and that the three-dimensional structure of ACTH is important for cAMP formation.

Reduction in rat thymocyte interphase death by calcium depletion.

Role of Ca ion in development of radiation damage of rat thymocytes was examined. Free DNA release, an expression of chromatin degradation, and the percentage of erythrosin B stained (dead) cells were increased after incubation of 1000 R X-irradiated thymocytes with normal Ca-containing medium. Incubation of the irradiated cells with Ca ion-depleted medium resulted in marked depression of free DNA release as well as of development of cell death. It was concluded from these results that Ca-dependent process(es) was involved in rat thymocyte interphase death.

The role of calcium ions in tetanic and post‐tetanic increase of miniature end‐plate potential frequency.

1. The role of Ca ions in transmitter release changes, during and after high frequency stimulation of the motor nerve (10--100 Hz), was examined at the frog neuromuscular junction. 2. The stimulation-induced changes in miniature end-plate potential frequency (f) resembled the changes in end-plate potential amplitude recently described by Magleby and Zengel (1975, 1976). 3. The effects of tetanic stimulation on f under inward electrochemical gradient for Ca ions were compared with those under reversed gradient and four differences were found: (a) The increase in f during the tetanus under reversed Ca gradient conditions is much smaller than with an inward Ca gradient. (b) The increase in f under reversed Ca gradient is preceded by a small decrease in f, whereas with an inward Ca gradient an immediate increase in f is observed. (c) After the termination of the tetanus with a reversed Ca gradient, there is a further increase in f, compared to a decrease with an inward Ca gradient. (d) The augmentation phase of post-tetanic potentiation was practically abolished. 4. The experimental results are explained by assuming that high frequency nerve stimulation causes an increase in transmitter release by at least two distinct processes: influx of Ca ions through the presynaptic membrane and release of Ca ions from intracellular stores. It is suggested that Na ions couple nerve activity to intracellular release of Ca.

Ca-induced arrest response in Triton-extracted lateral cilia ofMytilus gill

The role of Ca ions in the ciliary arrest response ofMytilus gill cilia was studied with Triton-extracted models. The cilia continue to beat when the Ca ion concentration is lower than about 10−7 M, but stop beating and incline in the direction of the recovery stroke as in the arrest response observed in the living lateral cilia when Ca ion concentration is raised above 10−7–10−6 M. ATP, Mg and Ca ions are all indispensable for the arrest response in the model system.

Stimulus-secretion coupling in pancreatic acinar cells: inhibitory effects of calcium removal and manganese addition on pancreozymin-induced amylase release.

The role of Ca ions in stimulus-secretion coupling has been analysed in the isolated and perfused rat pancreas. 2. The omission of [Ca2+]O diminished but did not abolish the release of amylase in response to continuous stimulation with 5 m-u. pancreozymin (Pz)/ml. The addition of Mn2+ (1-0 mM) to this Ca-deficient environment abolished the residual release of amylase. This was followed by a complete recovery of amylase output when the control [Ca2+]O was reestablished. 3. The addition of Mn2+ (1-0 mM) to the extracellular environment containing 2-5 mM-Ca2+ reversibly inhibited the Pz-induced release of amylase. 4. A kinetic scheme based on competition of Ca and Mn at a carrier in the acinar cell membrane could quantitatively explain the effects of Ca and Mn upon the Pz-induced amylase release. 5. These results support the view that the Ca2+ influx into the acinar cells is the major contributor to the rise in [Ca2+]i which, in turn, mediates the processes in the stimulus-secretion coupling in the exocrine pancreas, and suggest that the mode of Ca influx is a facilitated diffusion.

A shift of cellular calcium to a more slowly exchangeable fraction during contraction in guinea pig taenia coli.

Abstract It is now generally agreed that Ca ion is essential for the contraction of smooth muscle. On the role of Ca ion in the contraction cycle of smooth muscle, many electrophysiological studies have suggested that the action potential of the muscle cell is associated with an inward movement of Ca ions from anionic sites of cell membrane or from extracellular space and this Ca flow may initiate contractile response (1, 2). It has also been suggested from radioisotope studies (3–6) that contraction in smooth muscle may be triggered and maintained by release of Cellular Ca and/or by influx of extracelluar Ca.

A Shift of Cellular Calcium to A More Slowly Exchangeable Fraction During Contraction in Guinea Pig Taenia Coli

It is now generally agreed that Ca ion is essential for the contraction of smooth muscle. On the role of Ca ion in the contraction cycle of smooth muscle, many electrophysiological studies have suggested that the action potential of the muscle cell is associated with an inward movement of Ca ions from anionic sites of cell membrane or from extracellular space and this Ca flow may initiate contractile response (1, 2). It has also been suggested from radioisotope studies (3–6) that contraction in smooth muscle may be triggered and maintained by release of Cellular Ca and/or by influx of extracelluar Ca.

Possible role of Ca ions in the resting metabolism of frog sartorius muscle during potassium depolarization.

AbstractOxygen consumption and Ca exchangeability at different levels of potassium depolarization were studied in frog sartorius muscle. It was found that the changes in oxygen consumption parallel the changes in Ca exchangeability. Procaine (10−3 M) and CaCl2 (2.10−2 M) suppressed both extra oxygen consumption and Ca exchangeability at low values of depolarization. At higher values of depolarization procaine and CaCl2 differed in their action. Procaine favored inhibition of these processes, CaCl2 caused their activation. The effects of these compounds was not a result of a change in the membrane potential, since their effect on potassium depolarization was found to be small.Relations between oxygen consumption and Ca exchangeability similar to those observed at potassium depolarization seem to exist under conditions where caffeine was applied. It is proposed that the extra oxygen consumption caused by potassium depolarization or on application of caffeine and unaccompanied by mechanical changes is related to the release of Ca from its bound form. Oxygen consumption in isotonic sucrose solution was also studied, but some different data from the above were obtained.