calcium-induced calcium release (CICR)

Examples of calcium-induced calcium release (CICR) in the following topics:

• Regulatory Proteins

  • During stimulation of the muscle cell, the motor neuron 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.
  • This mechanism is called calcium-induced calcium release (CICR).
  • It is not understood whether the physical opening of the L-type calcium channels or the presence of calcium causes the ryanodine receptors to open.
  • Calcium remains in the sarcoplasmic reticulum until released by a stimulus.

• Mechanism and Contraction Events of Cardiac Muscle Fibers

  • Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release conducted through the intercalated discs.
  • In cardiac muscle, ECC is dependent on a phenomenon called calcium-induced calcium release (CICR), which involves the influx of calcium ions into the cell, triggering further release of ions into the cytoplasm.
  • The mechanism for CIRC is receptors within the cardiomyocyte that bind to calcium ions when calcium ion channels open during depolarization, releasing more calcium ions into the cell.
  • CICR creates a "plateau phase" in which the cell's charge stays slightly positive (depolarized) briefly before it becomes more negative as it repolarizes due to potassium ion influx.
  • An action potential, induced by the pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes, is conducted to contractile cardiomyocytes through gap junctions.

• Bone Tissue and the Effects of Aging

  • Bone resorption is the process by which osteoclasts break down bone and release the minerals, resulting in a transfer of calcium from bone to blood.
  • The osteoclast then induces an infolding of its cell membrane and secretes collagenase and other enzymes important in the resorption process.
  • High levels of calcium, magnesium, phosphate, and products of collagen will be released into the extracellular fluid as the osteoclasts tunnel into the mineralized bone.
  • Low levels of calcium stimulates the release of parathyroid hormone (PTH) from chief cells of the parathyroid gland.
  • High levels of calcium in the blood, on the other hand, lead to decreased PTH release from the parathyroid gland.

• Development of the Endocrine System

  • The thyroid also produces and releases the hormone calcitonin (thyrocalcitonin), which contributes to the regulation of blood calcium levels.
  • Thyrocalcitonin decreases the concentration of calcium in the blood.
  • Most of the calcium removed from the blood is stored in the bones.
  • TSH stimulates certain major rate-limiting steps in thyroxine secretion, and thereby alters its rate of release.
  • A variety of bodily defects, either dietary, hereditary, or disease induced, may decrease the amount of thyroxine released into the blood.

• Intracellular Hormone Receptors

  • At the target cell, the hormones are released from the carrier protein and diffuse across the lipid bilayer of the plasma membrane of the target cells.
  • The cell signaling pathways induced by the steroid hormones regulate specific genes within the cell's DNA.
  • The binding of calcitriol to the VDR allows the VDR to act as a transcription factor that modulates the gene expression of transport proteins that are involved in calcium absorption in the intestine.
  • VDR activation in the intestine, bone, kidney, and parathyroid gland cells leads to the maintenance of calcium and phosphorus levels in the blood and to the maintenance of bone content.

• Bacterial Transformation

  • Some species, upon cell death, release their DNA to be taken up by other cells; however, transformation works best with DNA from closely-related species.
  • Artificial competence can be induced in laboratory procedures that involve making the cell passively permeable to DNA, by exposing it to conditions that do not normally occur in nature.
  • Typically, the cells are incubated in a solution containing divalent cations; most commonly, calcium chloride solution under cold condition, which is then exposed to a pulse of heat shock.
  • However, the mechanism of the uptake of DNA via chemically-induced competence in this calcium chloride transformation method is unclear.

• Signaling Molecules

  • The types of molecules that serve as ligands are incredibly varied and range from small proteins to small ions like calcium (Ca2+).
  • It is able to diffuse directly across the plasma membrane; one of its roles is to interact with receptors in smooth muscle and induce relaxation of the tissue.
  • Nitroglycerin, a treatment for heart disease, acts by triggering the release of NO, which causes blood vessels to dilate (expand), thus restoring blood flow to the heart.