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Escorting the Sensor to the Channel
Receptors that trigger the release of calcium from the endoplasmic reticulum (ER) regulate various physiological processes, including fluid secretion from salivary glands. This type of calcium signaling requires calcium influx stimulated by depletion of calcium, stored in the ER, through a process involving calcium sensor protein STIM1 in the ER and the channel Orai1 at the plasma membrane. Ong et al. found that STIM2, a protein related to STIM1, helped traffic STIM1 to the junctions where the ER and plasma membrane are closely apposed, so that calcium entry through Orai1 is initiated in response to lower amounts of stimulation. The researchers showed that mice lacking STIM2 had reduced fluid secretion from their salivary glands.
