What is the major source of calcium in smooth muscle?
In smooth muscle the sarcoplasmic reticulum is the major intracellular source of Ca2+; mitochondria do not play a significant role in the physiological regulation of [Ca2+]i. Under pathological conditions mitochondria can reversibly accumulate large amounts of calcium.
What is the source of calcium in cardiac muscle?
In heart muscle cells, most of the calcium is stored inside a chamber named the sarcoplasmic reticulum. The calcium in the sarcoplasmic reticulum is released during heart muscle contraction and transported back inside the sarcoplasmic reticulum during relaxation.
Where is most of the calcium stored in skeletal muscle?
The sarcoplasmic reticulum within a muscle cells is where many calcium ions are stored and released.
What does calcium bind to in skeletal muscle contraction?
(1) Calcium binds to troponin C, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin. (2) ATP then binds to myosin.
Where does calcium come from in smooth muscle contraction?
Smooth muscle contraction, induced by acetylcholine through the muscarinic M3 receptor, starts with the release of Ca2+ from intracellular stores. Ca2+ binds calmodulin that is complexed with myosin light chain kinase.
Where does calcium-induced calcium release occur?
How are calcium levels increased within cells? Increases in intracellular calcium arise through either calcium influx across the plasma membrane or release from intracellular calcium stores, which is usually either the endoplasmic reticulum (ER) or, in muscle, the sarcoplasmic reticulum (SR).
What causes the release of calcium during skeletal muscle contraction?
When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding sites. The sarcoplasmic reticulum stores calcium ions, which it releases when a muscle cell is stimulated; the calcium ions then enable the cross-bridge muscle contraction cycle.
What causes the calcium to be released from where it is stored?
Calcium is stored in cells in a structure called the reticulum, a series of interconnected tubules and tiny sacs distributed throughout the cells. Small changes in sodium concentration can produce large changes in calcium stores. Increasing sodium increases the amount of calcium that can be released from the stores.
Does calcium bind to troponin or tropomyosin?
If present, calcium ions bind to troponin, causing conformational changes in troponin that allow tropomyosin to move away from the myosin-binding sites on actin.
Which of the following best describes the role of Ca2+ in muscle contraction?
Which of the following best describes the role of Ca2+ in muscle contraction? It binds to troponin, moving tropomyosin, so that myosin heads can bind to actin.
Does skeletal muscle require calcium for contraction?
Muscle contraction is known to be regulated by calcium. Calcium diffusing in the cytoplasm between myosin and actin filaments of the muscle fibrils causes the filaments to slide into each other, triggering the contraction of the entire muscle fiber.
Does calcium-induced calcium release occur in skeletal muscle?
Calcium-induced calcium release (CICR) was first discovered in skeletal muscle. CICR is defined as Ca2+ release by the action of Ca2+ alone without the simultaneous action of other activating processes.
What is the source of calcium for muscle contraction?
In skeletal muscles, intracellular calcium sources (SR) appear to be responsible for the largest elevations in calcium necessary for contraction. There is an initial trigger which is mediated at the plasma membrane and is represented by the physical juxtaposition of L-type voltage gated calcium channels and ryanodine receptors.
What triggers the release of calcium from the SR?
Calcium release from the SR via the RyR1 triggers muscle contraction and multiple cellular effects by binding of Ca 2+ to a variety of other target proteins. Reuptake of Ca 2+ from the cytoplasm into the SR is carried out by the SR calcium pump.
How is Ca2+ released from the skeletal muscle?
In skeletal muscle, activation of Ca 2+ release from the SR is controlled by a voltage sensor in the transverse tubular (tt) membrane ( 459 ). Elementary Ca 2+ signal events have recently been subcellularly localized in the skeletal muscle.
What causes muscle relaxation in calcium transport and storage systems?
VARIATIONS IN CALCIUM TRANSPORT AND STORAGE SYSTEMS 1. Structure and proposed function Skeletal muscle relaxation after a single twitch or a tetanic contraction is initiated by a fall in sarcoplasmic Ca 2+ concentration.