Increase in cytosolic calcium from intracellular storage, during smooth muscle contraction, is/are due to

In smooth muscle contraction, calcium channels are opened causing an influx of calcium into the cell. In smooth muscle cells, agonists such as neurotransmitters or hormones can induce an increase in (i) a release of intracellular stored calcium or/and an influxof extracellular calcium. ... These channels control phenomena such as smooth musclecells proliferation and/or contraction. (REF: TEXTBOOK OF MEDICAL PHYSIOLOGY GEETHA N 2 EDITION, PAGE NO - 59)