Question

** Integrative Question: Describe at least FIVE processes in neurons, myocytes (muscle cells skeletal, smooth, & cardiac), and secretory endocrine glands in which Calcium Ions (Ca++) function as important intracellular secondary messengers. Draw simple diagrams showing how calcium exerts its effect on cells in each of these cases (what cells and molecules does Ca++ act upon, and what is the result?).

Answer 1

Calcium ions are one type of second messengers and are responsible for many important physiological functions including muscle contraction, fertilization, and neurotransmitter release. The ions are normally bound or stored in intracellular components (such as the endoplasmic reticulum(ER)) and can be released during signal transduction.
Muscle Contractions
Contractions of skeletal muscle fiber are caused due to electrical stimulation. This process is caused by the depolarization of the transverse tubular junctions. Once depolarized the sarcoplasmic reticulm (SR) releases Ca2+ into the myoplasm where it will bind to a number of calcium sensitive buffers. The Ca2+ in the myoplasm will diffuse to Ca2+ regulator sites on the thin filaments. This leads to the actual contraction of the muscle
Contractions of smooth muscle fiber are dependent on how a Ca2+ influx occurs. When a Ca2+ influx occurs, cross bridges form between myosin and actin leading to the contraction of the muscle fibers. Influxes may occur from extracellular Ca2+ diffusion via ion channels. This can lead to three different results.
1:uniform increase in the Ca2+ concentration throughout the cell. This is responsible for increases in vascular diameters.
2:rapid time dependent change in the membrane potential which leads to a very quick and uniform increase of Ca2+. This can cause a spontaneous release of neurotransmitters via sympathetic or parasympathetic nerve channels
3:last potential result is a specific and localized subplasmalemmal Ca2+ release. This type of release increases the activation of protein kinase, and is seen in cardiac muscle where it causes excitation-concentration coupling
IP3 Ca2+ release is caused by activation of the IP3 receptor on the SR. These influxes are often spontaneous and localized as seen in the colon and portal vein, but may lead to a global Ca2+ wave as observed in many vascular tissues.
Neuron
In neurons, concomitant increases in cytosolic and mitochondrial Ca2+ are important for the synchronization of neuronal electrical activity with mitochondrial energy metabolism
It is necessary for the activation of isocitrate dehydrogenase, which is one of the key regulatory enzymes of the Krebs cycle.The ER's structural characteristics, ability to act as a Ca2+ sink, and specific Ca2+ releasing proteins, serve to create a system that may produce regenerative waves of Ca2+ release. These may communicate both locally and globally in the cell. These Ca2+ signals integrate extracellular and intracellular fluxes, and have been implicated to play roles in synaptic plasticity, memory, neurotransmitter release, neuronal excitability, and long term changes at the gene transcription level.
In glands
Parathyroid gland regulation
Parathormone:depend low ca level
Calcitonin:depend on high calcium level
Pancreatic enzyme secreation:ca act pancreatic acinar cell for secreation
Salivary gland: ca act on salivary acinar cell and increase fluid secreation
activation of fluid secretion is an increase in [Ca2+]i triggered by inositol 1,4,5‐trisphosphate (IP3)‐induced release of Ca2+ from ER via the IP3 receptor (IP3R).