This article is related to the #MB1004 module as it discusses how Ca ion concentration is modulated within the cell. There are two ways in which Ca conentration is controlled and this is through primary and secondary active transport. This article disscusses two types of channels which are known as CRAC channels and also SOC channels. Each of these channels are activated in response to a specific physiological change which helps to control the Ca concetration in the cell. - Hamdi Hussain