Ducts of acinar salivary glands in the cockroach Periplaneta americana are innervated by dopaminergic fibers and modify the NaCl-rich primary saliva by Na⁺ reabsorption and K⁺ secretion. An apical V-H⁺-ATPase seems to be crucial for saliva modification. We studied how dopamine (DA) affects intracellular pH (pH_i) and the contribution of the V-H⁺-ATPase in the regulation of pH_i using BCECF for ratiometric imaging. Results: DA causes a reversible maintained drop in pH_i. Its initial rapid phase can be isolated with bumetanide or in Ca²⁺-free saline. This phase is suppressed in Cl^--free saline and reduced by DIDS and acetazolamide. The later maintained acidification requires extracellular Ca²⁺ because a DA-induced depolarisation and massive [Na⁺]_i elevation causes Na⁺-Ca²⁺-exchanger (NCE)mediated Ca²⁺-entry. Ionomycin mimicks the DA-induced maintained acidification and can be blocked by La³⁺. Both findings suggest that Ca²⁺ extrusion via Ca²⁺/H⁺-ATPase (PMCA) activity maintains pH_i low. Recovery from DA-induced acidification is fully blocked in Na⁺-free saline combined with VH⁺-ATPase inhibition by concanamycin.

Conclusions: The DA-modulatable saliva modification (Na⁺ reabsorption) is accompanied by a large [Na⁺]_i elevation causing a pH_i drop by parallel NCE and PMCA activity. The V-H⁺ATPase contributes to pH_i homeostasis.