Fig. 1.

Pharmacological effects of pilocarpine and isoproterenol on primary saliva secretion from salivary gland acinar cells. Pilocarpine stimulates M₃ receptors, which induces a rise in the intracellular Ca²⁺ level thereby causing chiefly the activation of luminal Cl^– channels. Cl^– release mediates Na⁺ flow from the interstitium to the lumen, which consequently causes near-isosmolar water transfer through AQP5 and/or tight junctions. Isoproterenol activates β1-adrenergic receptors, causing chiefly the exocytosis of secretory granules containing salivary protein via the cAMP/PKA cascade.