Fig. 4. Microfluorometric measurements of oxygen content in the lumen of isolated salivary gland tubules injected with polystyrene beads containing the O₂-sensitive luminescent dye PtPFPP. 100% O₂ concentration in A–C corresponds to the O₂ content in the bath PS, which is in equilibrium with ambient air. (A) 10 nmol l^–1 5-HT stimulates cellular respiration and a drop in luminal O₂ concentration that is not significantly reduced in the presence of concanamycin A (A,D). The 8-CPT-cAMP-induced drop in luminal O₂ concentration is significantly reduced by concanamycin A (B,D). Application of 1 µmol l^–1 thapsigargin in Ca²⁺-free PS causes an increase in luminal O₂ concentration, and the 5-HT-induced drop in luminal O₂ concentration is significantly reduced under these conditions (C,D). Data in D are means ± s.e.m.; the number of experiments is given in parentheses; ^*P<0.05.