Role of Ca2+ ions in mechanisms of cell signaling

molarity and mass, after Na, Cl, Mn, S.

Melting point 1115 K ​(842 °C, ​1548 °F)
Boiling point 1757 K ​(1484 °C, ​2703 °F)
Density near r.t. 1.55 g/cm3
when liquid, at m.p.1.378 g/cm3

Calcium is a soft grayish-yellow alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust.

In skin 7-dehydrocholesterol is converted (not enzymatically) into cholecalciferol (vitamin D3);

– in kidney the formation of calcitriol is catalyzed by 1α-hydroxylase.

In the cells of intestine, calcitriol induce the synthesis of Са2+-transporting proteins, which provide absorption of calcium ions and transport to the blood.
In kidneys, calcitriol stimulate reabsorption of calcium and phosphate ions.

and is immediately bound to calbindin. Calbindin transfers the calcium directly into the epithelial cell's ER, through which the calcium is transferred to the basal membrane on the opposite side of the cell, without entering its cytosol.

From there TRPV6 (transient receptor potential cation channel) and calcium pumps (PMCA1- Plasma membrane Ca2+ ATPase ) actively
transport calcium into the body. Active transport of calcium occurs primarily in the duodenum portion of the intestine when calcium intake is low; and through passive paracellular transport in the jejunum and ileum parts when calcium intake is high, independently of Vitamin D level.

calcium composition)

Functioning of heart

Blood clotting

Apoptosis

Regulation of enzyme activity

Activation of hormone synthesis

molecules (Protein kinases)
Са2+ binds with inactive cytoplasmic modulators of effector molecules and activates them.

are the effectors of phosphorylation is a phosphotransferase enzyme that catalyzes the interconversion of adenine nucleotides, and plays an important role in cellular energy homeostasis (Protein kinase C).

Co factors -> nitric oxide synthase, protein phosphatases (Calcinevrin-Phosphatase IIB), and adenylate kinase, but calcium activates these enzymes in allosteric regulation in a complex with calmodulin

a hinge region:
*C1 domain, present in all of the isoforms of PKC has a binding site for DAG
*C2 domain acts as a Ca2+ sensor
*Catalytic Region brings about phosphorylation Ser/Thr a.a. of proteins
*Upon activation, translocated to the plasma membrane

C1 domain

C2 domain

Ca2+

DAG

located on the cytosolic face of the plasma membrane. Annexin A1 protein has an apparent relative molecular mass of 40 kDa with phospholipase A2 inhibitory activity.

*In other words, glucocorticoids not only suppress immune response, but also inhibit the two main products of inflammation, prostaglandins and leukotrienes.

Annexin

Glucocorticoids (such as budesonide, cortisol, and beclomethasone)

Glucocorticoid Receptor

Synthesis of annexin A1

annexin

Ca2+

Phospholipase A2

Eicosanoid production

Inflammatory events (epithelial adhesion, emigration, chemotaxis, phagocytosis, etc.)

the pre-synaptic terminal. Most neurons contain at least two types of synaptic vesicles, small (about 50 nm diameter) and large (70-200 nm diameter). Neurotransmitters are released in quantal units as each vesicle contains a given amount of transmitter. The vesicles are concentrated near "active zones," dense bodies along the pre-synaptic membrane where neurotransmitter release occurs. At rest, only a small number of vesicles are actually positioned at the active zones. Rather, most are held near the active zones by the proteins synapsin I and actin. Synapsin I, a protein associated with the vesicle membrane, binds to actin, a cytoskeletal filament holding the vesicles in place.

release; when Ca2+ channels are blocked, neurotransmitter release is inhibited. When the action potential reaches the nerve terminal, voltage-dependent Ca2+ channels open and Ca2+ rushes into the neuron terminal due to a greater extracellular concentration.
Ca2+ channels appear to be localized near the active zones of the vesicular membrane. In the giant squid neuron, it has been found that Ca2+ influx is ten times greater in the area of the active zone than elsewhere in the neuron. Furthermore, during an action potential Ca2+ concentration at the active zone can rise one-thousand fold, from 100 nM (nano-molar concentration) to 100 micro-M within a few hundred microseconds. The observation of intramembranous proteins thought to be Ca2+ channels near active zones is consistent with rapid neurotransmitter release following Ca2+ influx.

been appreciated for decades. For example, it is well accepted that intracellular calcium release from the sarcoplasmic reticulum (SR) is required for cardiac muscle contraction. Indeed, with each heart beat the calcium concentration in the cytosol of cardiac myocytes is elevated approximately 10-fold from a resting level of ∼100 nM to ∼1 μM.
Presumably, a defect in signaling that prevents effective elevation of cytosolic calcium would impair contractility as the contraction of heart muscle is directly determined by the level of calcium elevation during systole. Similarly, a defect in the removal of calcium from the cytosol during diastole would impair cardiac relaxation, which is critically important in that it allows the heart chambers to refill with blood in preparation for the next beat.

mechanism unique to cardiac muscle called calcium-induced calcium release. CICR is A process whereby calcium can trigger release of further calcium from the muscle sarcoplasmic reticulum.

releases the neurotransmitter acetylcholine, which then binds to a post-synaptic nicotinic acetylcholine receptor. The inward flow of calcium from the L-type calcium channels activates ryanodine receptors to release calcium ions from the sarcoplasmic reticulum.

stimulus (action potential) into a mechanical response (muscle contraction).
Calcium-induced calcium release involves the conduction of calcium ions into the cardiomyocyte, triggering further release of ions into the cytoplasm. Calcium prolongs the duration of muscle cell depolarization before repolarization occurs. Contraction in cardiac muscle occurs due to the binding of the myosin head to adenosine triphosphate (ATP), which then pulls the actin filaments to the center of the sarcomere, the mechanical force of contraction. In the sliding filament model, myosin filaments slide along actin filaments to shorten or lengthen the muscle fiber for contraction and relaxation

steps: An action potential, induced by the pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes, is conducted to contractile cardiomyocytes through gap junctions. As the action potential travels between sarcomeres, it activates the calcium channels in the T-tubules, resulting in an influx of calcium ions into the cardiomyocyte. Calcium in the cytoplasm then binds to cardiac troponin-C, which moves the troponin complex away from the actin binding site. This removal of the troponin complex frees the actin to be bound by myosin and initiates contraction. The myosin head binds to ATP and pulls the actin filaments toward the center of the sarcomere, contracting the muscle.
Intracellular calcium is then removed by the sarcoplasmic reticulum, dropping intracellular calcium concentration, returning the troponin complex to its inhibiting position on the active site of actin, and effectively ending contraction as the actin filaments return to their initial position, relaxing the muscle

protein that separates the actin monomers;
*G-proteins, rupturing actin filaments-> gelglin, vorsin, sverinin, adzeverin, destrin and cofilin;
*Protein-> GCap39, blocking the ends of actin filaments;
*A-actinin, protein, cross-linking actin filaments.

PIP2
Phosphoinozitoldiphosphate

Polymerization

Ca2+

Depolymerization

of Ca2 + in the blood are parathyroid hormone, calcitriol and calcitonin.
Parathyroid hormone
Parathyroid hormone (PTH) is a single-chain polypeptide consisting of 84 amino acid residues (about 9.5 kD), whose action is aimed at increasing the concentration of calcium ions and reducing the concentration of phosphates in the blood plasma.

peptide (25a.a) is cleaved

Pro-hormone

Pro-hormone

GA

Hormone maturation (84 a.a.)

N-terminal peptides containing 34 amino acid residues have complete biological activity and are secreted by glands along with mature parathyroid hormone. It is the N-terminal peptide that is responsible for binding to the receptors on the target cells. The role of the C-terminal fragment is not exactly established. The rate of hormone degradation decreases with a low concentration of calcium ions and increases if the concentration of calcium ions is high.
The secretion of PTH is regulated by the level of calcium ions in the plasma: the hormone is secreted in response to a decrease in the concentration of calcium in the blood

stimulates the mobilization of calcium from bones
2 – stimulate reabsorption of calcium ions in distal tubules of the kidneys;
3 - Activates the formation of calcitriol, 1,25 (OH) 2D3 in the kidneys, which leads to stimulation of absorption of Ca2 + in the intestine;
4 - increases the concentration of calcium in the intercellular fluid, inhibits the secretion of PTH. (МКЖ - межклеточная жидкость)

32 amino acid residues with one disulfide bond. The hormone is secreted by parafollicular K-cells of the thyroid gland or C-cells of parathyroid glands in the form of a high-molecular precursor protein. Secretion of calcitonin increases with increasing concentration of Ca2 + and decreases with decreasing Ca2 + concentration in the blood.
Calcitonin is a parathyroid hormone antagonist.
It inhibits: 1) the release of Ca2 + from the bone, reducing the activity of osteoclasts.
2) inhibits tubular reabsorption calcium ions, stimulating their excretion by kidneys with urea.
*The rate of secretion of calcitonin in women strongly depends on the level of estrogens. With a lack of estrogens, the secretion of calcitonin decreases. This causes an acceleration of the mobilization of calcium from bone tissue, which leads to the development of osteoporosis.