Examples of voltage-dependent calcium channels in the following topics:
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- Upon the arrival of an action potential at the presynaptic neuron terminal, voltage-dependent calcium channels open and Ca2+ ions flow from the extracellular fluid into the presynaptic neuron's cytosol.
- The depolarization activates L-type, voltage-dependent calcium channels (dihydropyridine receptors) in the T-tubule membrane, which are in close proximity to calcium-release channels (ryanodine receptors) in the adjacent sarcoplasmic reticulum.
- As intracellular calcium levels rise, the motor proteins responsible for the contractile response are able to interact, as shown in Figure 3, to form cross-bridges and undergo shortening.
- The binding of acetylcholine at the motor end plate leads to intracellular calcium release and interactions between myofibrils to elicit contraction.
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- Voltage-gated sodium ion channels contribute to the "spike" of a neuron's action potential.
- For example, ion channels can be voltage-sensitive in that they open and close in response to the voltage across the membrane.
- Voltage-gated ion channels, also known as voltage-dependent ion channels, are channels whose permeability is influenced by the membrane potential.
- They form another very large group, with each member having a particular ion selectivity and a particular voltage dependence.
- Many are also time-dependent—in other words, they do not respond immediately to a voltage change, but only after a delay.
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- 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.
- 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.
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- The depolarization, also called the rising phase, is caused when positively charged sodium ions (Na+) suddenly rush through open voltage-gated sodium channels into a neuron.
- The repolarization or falling phase is caused by the slow closing of sodium channels and the opening of voltage-gated potassium channels.
- As the sodium ion entry declines, the slow voltage-gated potassium channels open and potassium ions rush out of the cell.
- Hyperpolarization is a phase where some potassium channels remain open and sodium channels reset.
- The propagation of action potential is independent of stimulus strength but dependent on refractory periods.
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- Membrane potential (also transmembrane potential or membrane voltage) is the difference in electrical potential between the interior and the exterior of a biological cell.
- The opening and closing of ion channels can induce a departure from the resting potential.
- This is called a depolarization if the interior voltage becomes more positive (say from –70 mV to –60 mV), or a hyperpolarization if the interior voltage becomes more negative (say from –70 mV to –80 mV).
- The changes in membrane potential can be small or larger (graded potentials) depending on how many ion channels are activated and what type they are.
- Action potentials are generated by the activation of certain voltage-gated ion channels.
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- Each gap junction channel is
made up of two half channels (hemichannels), one in each cell’s membrane.
- Each of these half
channels is called a connexon.
- Examples of
this includes calcium ions and cAMP (cyclic adenosine monophosphate).
- Depending on the type of gap junction in
question, molecules can pass evenly in both directions, or asymmetrically, so in some gap junctions the molecules
will move in one direction faster than in the other direction.
- The ability of the channel to open or close is made possible in
part to calcium ions, which induce a reversible conformational change in the
connexin molecules, which leads to the closure of a channel at its extracellular
surface.
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- Gene PKD-1 is located on chromosome 16, and codes for a protein involved in regulation of cell cycle and intracellular calcium transport in epithelial cells; it is responsible for 85% of the cases of ADPKD.
- PKD-2, on chromosome 4, codes for a group of voltage-linked calcium channels.
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- Which diuretic is best for you depends on your health and the condition being treated.
- Aldosterone normally adds sodium channels in the principal cells of the collecting duct and late distal tubule of the nephron.
- The term "calcium-sparing diuretic" is sometimes used to identify agents that result in a relatively low rate of excretion of calcium.
- The reduced concentration of calcium in the urine can lead to an increased rate of calcium in serum.
- The sparing effect on calcium can be beneficial in hypocalcemia and unwanted in hypercalcemia.
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- The composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood.
- The composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood.
- The cell membrane separates cytosol from extracellular fluid, but can pass through the membrane via specialized channels and pumps during passive and active transport.
- The cations include: sodium (Na+ = 136-145 mEq/L), potassium (K+ = 3.5-5.5 mEq/L) and calcium (Ca2+ = 8.4-10.5 mEq/L).
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- Downstream effectors of cAMP include the cAMP-dependent protein, kinase (PKA), which mediates some of the intracellular events following hormone binding.
- Smooth muscle behavior is variable depending on anatomical location.
- The former interacts with calcium channels of the endoplasmic and sarcoplasmic reticulum, thus changing the calcium content in a cell.