1. Basolateral Fluid Secretion Apical endoplasmic reticulum Ca2+ store
nucleus
Fluid
Secretion
secretory vesicles
Introduce polarised salivary acinar cells. (click) Easy to tell which end is which …. nucleus at basolateral pole (click) secretory vesicles at apical pole. (click) Endoplasmic reticulum (mainly) basolateral around nucleus …. also Ca2+ store. (click)
Apical

2. Fluid Secretion M3 muscarinic receptor acetylcholine G-protein
inositol 1,4,5 trisphosphate
IP3
phospholipase C
Fluid
Secretion
muscarinic acetylcholine receptor - 7 membrane domains (click) linked via G-protein to phospholipase C (click) acetylcholine is the physiological ligand (click) Binding to the receptor activates the G protein, the active α subunit dissociates from the β γ subunits and activates phospholipase C (click) adenylate cyclase produces inositol 1,4,5 trisphosphate, IP3 (click) ACh binding leads to IP3 production (click)

3. [Ca2+] Fluid Secretion K+ Na+ Cl- water receptor activation increased
[Ca2+]i
[Ca2+]
ion channel
activation
fluid & electrolyte
secretion
IP3
Fluid
Secretion
IP3 is a cytoplasmic 2nd messenger and diffuses through the cell (click) causing an increase in intracellular Ca2+ activity (click) which activates an apical Cl- channel (click) .. and a basolateral K+ channel (click) The resulting transcellular electrical gradient drags Na+ from the basolateral side of the acinus into the lumen (click) NaCl in the acinus lumen drags water into the lumen by osmosis
Na+
Cl-
water