1. Phospholipase C (PLC) Inositol phosphates + Ca2+OH
OPO3 OH HO OH
OPO3 OH OH HO OH
OPO3
INOSITOL
INOSITOL
TRIPHOSPHATE
(IP3)

2. Production of IP3 and DAG
BRADYKININ
Phospholipase C
phosphatidyl
inositol P2
(PIP2)
phosphatidyl
inositol
ATP
phosphatases
IP3
inositol
ATP
DAG
phosphatidic
acid

3. Ca2+ Production PLC PIP2 DAG IP3 Endoplasmic reticulum Ca2+ store Ca2+
INCREASED CONTRACTION
SMOOTH MUSCLE
CARDIAC MUSCLE
INCREASED SECRETION
FLUIDS
HORMONES
TRANSMITTERS
Endoplasmic
reticulum
Ca2+ store
Ca2+

4. Note rise in [Ca2+] may be transient because Ca2+ is rapidly depleted
the response can be sustained if the Ca2+ is refilled directly from the extracellular space
refilling stores may be the job of IP4

5. Ca2+ Release Ca2+ + + Ca2+ PIP2 IP4 IP3
Note - this mechanism is still speculative