<prompt> Source of calcium for smooth muscle contractionInflux into intracellular store through IP3 receptor Ca2 channelEfflux through voltage - gated Ca2 channelEfflux through ligand - gated Ca2 channelCombination of influx of Ca2 through voltage - gated, ligand gated Ca2channel  <response>: Ca2 plays a prominent role in the initiation of contraction of smooth muscle. Depending on the activating stimulus, Ca2increase can be due to influx through voltage- or ligand-gated plasma membrane channels, efflux from intracellular stores through the RyR, efflux from intracellular stores through the inositol trisphosphate receptor IP3R Ca2channel, or a combination of these channels. 