ויסות משוב של ריכוז סידן

In an unstimulated cell, calcium concentration in the ER lumen and  the extracellular space is much higher than in the cytosol.

Activated GPCR stimulates phospholipase C-beta to produce IP3, which opens IP3-gated calcium channels on the ER membrane.

An efflux of calcium induces the opening of adjacent calcium channels by positive feedback. This increases calcium concentration and generates a calcium wave that rapidly moves through the cytosol. The spikes in calcium levels are translated into cellular responses such as hormone secretion, platelet aggregation, and zygote division.

If the calcium levels get too high, these channels close, halting calcium release by negative feedback. Calcium pumps on the plasma membrane drive out excess calcium, restoring them to the resting state.

As cytosolic calcium levels drop, the calcium channels open, triggering another cycle of calcium release.

Such repeated rise and fall in cytosolic calcium levels results in calcium oscillation. The oscillating calcium induces repetitive cellular actions such as contraction and relaxation of muscles during exercise.