Fig. 8

Schematic illustration for pH_i regulation during HCO₃ ⁻ secretion in rat parotid intralobular ducts. Sympathetic β-adrenergic stimulation induces activation of the carbonic anhydrase (CA) rather than the Na⁺–H⁺ exchanger (NHE), whereas parasympathetic muscarinic stimulation activates NHE on the basolateral membrane at least partially via Ca²⁺-calmodulin. Both mechanisms facilitate HCO₃ ⁻ secretion through the Cl⁻ channels activated by the stimulations. Thick arrows indicate the rate-limiting activation