Calcium levels must be maintained within certain limits in cells. Calcium is often considered a life or death signal in that, use of Calcium can be the difference between cell survival or cell death.

Extracellular Calcium levels range between 2-5 mM.
Intracellular Calcium levels range between 100-200 nM.

The Endoplasmic Reticulum and Nucleus can act as Intracellular stores of Calcium.

Homeostasis of Calcium is achieved by a delicate balance of multiple factors.

Calcium entry is essential for Calcium Homeostasis.

Voltage operated receptors:
L type - HIGH voltage, long lasting effects. BAYK is an agonist, DHPs is an antagonist.

N type - HIGH voltage, Fast inactivation

T type - LOW voltage, fast inactivation.

Receptor Operated Calcium Channels:

NMDA Receptor - Glutamate activated Calcium channel. Depolarising of cell is neccessary to remove Magnesium block to get Calcium flow

AMPA Receptor - Allows Calcium entry into cell

M2 receptor decides Calcium permeability.

Q - Glutamine form is permeable while the

R - Arginine form is impermeable to Calcium

Calcium can be used in a cell to effect Potassium hyperpolarisation of a cell, Chloride depolarisation of a cell.

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Hows does Calcium enter a cell and through what channels