Ca 2+ signatures: The role of Ca 2+ -ATPases

FEBS Journal, 2009

Calcium ions (Ca 2+) control and influence a diverse array of cellular processes such as muscle contraction, gene expression, energy metabolism, proliferation and cell death. In order to extensively control cellular activity, it is necessary to regulate Ca 2+ signals (changes in Ca 2+ concentration) in 3D space, time and amplitude. Cells normally maintain a low resting 'free' Ca 2+ concentration in the cytosol ([Ca 2+ ] c) of 100 nm. This contrasts with 1 mm in the extracellular fluid of terrestrial animals and 10 mm in seawater. In order to achieve this low resting [Ca 2+ ] c , cells remove Ca 2+ using two energy-dependent mechanisms. First, plasma membrane Ca 2+ ATPases (PMCA) pump Ca 2+ out of the cell against a concentration gradient, consuming ATP in the process. Second, the Na +-Ca 2+ exchanger (NCX) uses the electrochemical Na + gradient; one Ca 2+ being extruded for every three Na + ions entering. In addition, eukaryotic cells can sequester Ca 2+ into intracellular organelles, in particular the endoplasmic reticulum (ER). Organellar Ca 2+ sequestration requires either ATP hydrolysis or a favourable electrochemical gradient. Ca 2+ channels in the plasma membrane or release channels on Ca 2+-containing organelles help deliver Ca 2+ to the required cellular location. This enables the generation of Ca 2+ signals that can be small or large in amplitude, restricted to a small microdomain or global across the cell. Ca 2+ signals can be of variable duration lasting from a few milliseconds to many hours (Fig. 1A). They can either be simple Ca 2+ elevations or

In the plants being exposed to environmental stresses, ion channels are likely activated to convert these external stimuli into intracellular signals. Among the ions taken up by the plant cells, Ca2+ plays an essential role as an intracellular secondary messenger in plants and thus the cytoplasmic free Ca2+ concentration ([Ca2+]c) is strictly regulated. Signal transduction pathways mediated by the changes in the [Ca2+]c is termed Ca2+ signaling, and are mainly initiated by the activation of Ca2+-permeable channels. When Ca2+ channels are activated in response to a variety stimuli, a drastic increase in the [Ca2+]c is induced and the entered free Ca2+ binds to the sets of Ca2+-regulated proteins such as calmodulin and calcium dependent protein kinases to modify the activities or affinities of these proteins in binding to specific targets. To date, a large body of electro-physiological and molecular biological studies has revealed that plants possess several Ca2+ channels belonging to distinct types with different gating mechanisms, and a variety of genes for Ca2+-permeable channels have been isolated and functionally characterized. In this chapter, the topics covered include (1) the characteristics of molecularly cloned Ca2+-permeable channels including voltage-dependent Ca2+-permeable channels, cyclic nucleotide-gated cation channel, and ionotropic glutamate receptor; (2) the roles of Ca2+ at the key steps during environmental responses and regulations of growth and developments (eg. stomatal movements, tropisms, nutrient allocations, flowering, pollination, fertilization, and etc.); (3) the Ca2+-dependent metabolic regulation of reactive oxygen species levels; and (4) the Ca2+-mediated response during plant defense mechanism against pathogenic microorganisms.

Floriculture, Ornamental and Plant Biotechnology: Advances and Topical Issues Vol. III, 2006

In the plants being exposed to environmental stresses, ion channels are likely activated to convert these external stimuli into intracellular signals. Among the ions taken up by the plant cells, Ca2+ plays an essential role as an intracellular secondary messenger in plants and thus the cytoplasmic free Ca2+ concentration ([Ca2+]c) is strictly regulated. Signal transduction pathways mediated by the changes in the [Ca2+]c is termed Ca2+ signaling, and are mainly initiated by the activation of Ca2+-permeable channels. When Ca2+ channels are activated in response to a variety stimuli, a drastic increase in the [Ca2+]c is induced and the entered free Ca2+ binds to the sets of Ca2+-regulated proteins such as calmodulin and calcium dependent protein kinases to modify the activities or affinities of these proteins in binding to specific targets. To date, a large body of electro-physiological and molecular biological studies has revealed that plants possess several Ca2+ channels belonging to distinct types with different gating mechanisms, and a variety of genes for Ca2+-permeable channels have been isolated and functionally characterized. In this chapter, the topics covered include (1) the characteristics of molecularly cloned Ca2+-permeable channels including voltage-dependent Ca2+-permeable channels, cyclic nucleotide-gated cation channel, and ionotropic glutamate receptor; (2) the roles of Ca2+ at the key steps during environmental responses and regulations of growth and developments (eg. stomatal movements, tropisms, nutrient allocations, flowering, pollination, fertilization, and etc.); (3) the Ca2+-dependent metabolic regulation of reactive oxygen species levels; and (4) the Ca2+-mediated response during plant defense mechanism against pathogenic microorganisms.

The Plant Journal, 2007

The putative two-pore Ca 2+ channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K +-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca 2+-activated slow vacuolar (SV) currents, which were increased in AtTPC1-overexpressing Arabidopsis compared to the wild-type. A Ca 2+-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA-and CO 2-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K +-, and Ca 2+-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono-and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca 2+ entry into the cytosol. Ca 2+ responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-overexpressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca 2+ signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca 2+ concentration and biotic factors (elf18, flg22). In good agreement, stimulus-and Ca 2+-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca 2+-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca 2+ homeostasis.

Annals of botany, 2003

Calcium ions function as intracellular second messengers in regulating a plethora of cellular processes from acclimative stress responses to survival and programmed cell death. The generation of specificity in Ca2+ signals is dependent on influx and efflux from the extracellular milieu, cytosol and intracellular organelles. One aspect of plant Ca2+ signalling that is currently attracting a great deal of interest is how 'Ca2+-signatures', specific spatio-temporal changes in cytosolic-free Ca2+, encode the necessary information to bring about this range of physiological responses. Here, current information is reviewed on how Ca2+-signatures are generated in plant cells and how stimulus-specific information can be encoded in the form of Ca2+-signatures.

Science Signaling, 2015

cytosolic Ca 2+ is regulated by multiple proteins, including the plasma membrane Ca 2+ -ATPases (PMCAs), which use ATP to transport Ca 2+ out of cells. PMCA isoforms exhibit different kinetic and regulatory properties, thus the presence and relative abundance of individual isoforms may help shape Ca 2+ transients and cellular responses. We studied the effects of three PMCA isoforms (PMCA4a, PMCA4b, PMCA2b) on Ca 2+ transients elicited by conditions that trigger storeoperated Ca 2+ entry (SOCE) and that blocked Ca 2+ uptake into the endoplasmic reticulum in HeLa cells, human embryonic kidney (HEK) 293 cells, or primary endothelial cell isolated from human umbilical cord veins (HUVECs). The slowly activating PMCA4b isoform produced longlasting Ca 2+ oscillations in response to SOCE. The fast-activating isoforms PMCA2b and PMCA4a produced different effects. PMCA2b resulted in rapid and highly PMCA abundancesensitive clearance of SOCE-mediated Ca 2+ transients; whereas PMCA4a reduced cytosolic Ca 2+ resulting in the establishment of a higher than baseline cytosolic Ca 2+ concentration.

Environmental Adaptations and Stress Tolerance of Plants in the Era of Climate Change, 2011

Science China Life Sciences, 2012

As a highly versatile intracellular signal, calcium (Ca 2+) regulates many different cellular processes in both animal and plant systems. Disruption of Ca 2+ homeostasis contributes to several human diseases. Owing to the importance of Ca 2+ signalling, its research is now an active field in life science. There are numerous Ca 2+ signalling systems, consisting of a diverse array of signalling units that deliver Ca 2+ signals with different spatial and temporal properties [1,2], playing roles in ubiquitous biological processes including gene regulation, fuel generation, substance transport, hormone and neurotransmitter secretion, cell motility and muscle contraction [3]. Consequently, exquisite homeostasis of Ca 2+ cycling is the key for health of humans, the disruption of which is related to many human diseases such as heart failure, neuron-degeneration, and diabetes [46]. Many remarkable achievements have greatly enhanced our understanding of Ca 2+ signaling, including those from Chinese scientists [710]. The 17th International Symposium on Ca 2+-binding Proteins and Ca 2+ Function in Health and Disease was held in Beijing, China, on July 16-20, 2011 [11], accompany which, a special issue of Science China Life Sciences was published for transducing Ca 2+ signals to effectors. The first part focused on the mechanisms in maintaining a low cytosolic level of Ca 2+ , with two articles reviewing the properties of the plasma membrane calcium ATPases (PMCA) in ejecting Ca 2+ into the extracellular space. First, Carafoli [12] reviewed the role of the plasma membrane calcium pump, PMCA2, in the hearing process. As an im-Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Current biology, 2002

Recent studies have expanded the number of channel types and messengers that lead to Ca 2+ signals within cells. Furthermore, we are beginning to understand the complex interplay between different sources of Ca 2+ .

Metal Ions in Life Sciences, 2012

2000

General Physiology and Biophysics

Postsynaptic potential is only one aspect of extensive communication between neurons and their synapses. Besides generating of potential changes by activation of ionic channels, neurotransmitters may activate receptors linked with the transient concentration changes of one or several intracellular second messengers, including calcium ions (Ca2+). In the neuronal cells calcium triggers and controls specific processes. Transient changes of Ca2+ concentration within the cell play an important signal role by coupling electrical and chemical impulses generated on the plasma membrane with the intracellular systems of responses. Several proteins and/or protein complexes, whose functions are directly controlled by calcium, have been identified in the neuronal cells. Their biochemical properties and physiological importance as well as cellular localization are discussed in this paper.

Planta, 1992

The regulation of cytosolic Ca2+ has been investigated in growing root-hair cells of Sinapis alba L. with special emphasis on the role of the plasmamembrane Ca2+-ATPase. For this purpose, erythrosin B was used to inhibit the Ca2+-ATPase, and the Ca2+ ionophore A23187 was applied to manipulate cytosolic free [Ca2+] which was then measured with Ca2+-selective microelectrodes. (i) At 0.01 μM, A23187 had no effect on the membrane potential but enhanced the Ca2+ permeability of the plasma membrane. Higher concentrations of this ionophore strongly depolarized the cells, also in the presence of cyanide. (ii) Unexpectedly, A23187 first caused a decrease in cytosolic Ca2+ by 0.2 to 0.3 pCa units and a cytosolic acidification by about 0.5 pH units, (iii) The depletion of cytosolic free Ca2+ spontaneously reversed and became an increase, a process which strongly depended on the external Ca2+ concentration, (iv) Upon removal of A23187, the cytosolic free [Ca2+] returned to its steady-state level, a process which was inhibited by erythrosin B. We suggest that the first reaction to the intruding Ca2+ is an activation of Ca2+ transporters (e.g. ATPases at the endoplasmic reticulum and the plasma membrane) which rapidly remove Ca2+ from the cytosol. The two observations that after the addition of A23187, (i) Ca2+ gradients as steep as-600 mV could be maintained and (ii) the cytosolic pH rapidly and immediately decreased without recovery indicate that the Ca2+-exporting plasma-membrane ATPase is physiologically connected to the electrochemical pH gradient, and probably works as an nH+/Ca2+-ATPase. Based on the finding that the Ca2+-ATPase inhibitor erythrosin B had no effect on cytosolic Ca2+, but caused a strong Ca2+ increase after the addion of A23187 we conclude that these cells, at least in the short term, have enough metabolic energy to balance the loss in transport activity caused by inhibition of the primary Ca2+-pump. We further conclude that this ATPase is a major Ca2+ regulator in stress situations where the cytosolic Ca2+ has been shifted from its steady-state level, as may be the case during processes of signal transduction.

Science China-life Sciences, 2011