contraction of smooth muscle is depends on calcium
influx.
Calcium level within the smooth
muscle increases by various means like depolarisation,
hormones, neurotransmitters which cause Calcium to
enter the cell through the L-type channel located
in the membrane.
Calcium released by L-type
channel or IP3Rs downstream from
Gp-coupled cell surface receptors cause smooth muscle
contraction.
Smooth muscle contraction gets initiated by
calcium.
Calcium binds to calmodulin and activate
myosin light chain kinase enzyme.
These enzyme myosin light chain kinase
pgosphorylates myosin light chain which leads to smooth
muscle contraction.
Calcium may also initiate the contraction of
smooth muscle by binding direct to myosin.