Intracellular pH changes induced by exposure to weak acids and bases in submandibular cells of early postnatal rats

Enhancement of delta aminolevulinic acid-photodynamic therapy in vivo by decreasing tumor pH with glucose and amiloride

OBJECTIVES/HYPOTHESIS

Delta aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) is a fluorescent sensitizer that permits detection and treatment of squamous cell carcinoma of the oral cavity. An exogenously induced decrease in tissue pH was evaluated for its effect in enhancing cellular uptake of ALA and facilitating its transformation into PpIX.

STUDY DESIGN

Mice grafted with HT29 colonic cancers had been given glucose and amiloride to modify the pH of tissues. Influence of pH changes has been evaluated on ALA-induced PPIX fluorescence by optic fiber spectrofluorimetry as well as on tumor growth.

METHODS

RESULTS

The pH in HT 29 tumor decreased from 7.1 to 6.67 (P < .05) after intraperitoneal injection of glucose and amiloride. The PpIX fluorescence ratios in tumor or muscle before, between, and 2 hours after glucose and amiloride injection were not higher than control ratios. Aminolevulinic acid-photodynamic therapy was more efficient on HT 29 tumor-bearing mice when the pH value was decreased with glucose and amiloride, showing a difference in the tumor growth index ratio from the 1st to 14th day of 22% between amiloride-glucose aminolevulinic acid-photodynamic therapy and aminolevulinic acid-photodynamic therapy alone (P < .05).

CONCLUSIONS

Glucose and amiloride did not change PpIX fluorescence in HT 29 tumor after intraperitoneal injection of aminolevulinic acid but enhanced aminolevulinic acid-photodynamic therapy efficacy. This was probably a result of mechanisms other than an increase in aminolevulinic acid cellular penetration and PpIX production, such as susceptibility to free radical toxicity or alteration of cellular repair enzymes under acidotic conditions. If a decrease of pH induces a more efficient photodynamic therapy as suggested by our results, an easier way to obtain this decrease than glucose and amiloride would be necessary for clinical applications.

Influenza M2 proton channel activity selectively inhibits trans-Golgi network release of apical membrane and secreted proteins in polarized Madin-Darby canine kidney cells

The function of acidification in protein sorting along the biosynthetic pathway has been difficult to elucidate, in part because reagents used to alter organelle pH affect all acidified compartments and are poorly reversible. We have used a novel approach to examine the role of acidification in protein sorting in polarized Madin-Darby canine kidney (MDCK) cells. We expressed the influenza virus M2 protein, an acid-activated ion channel that equilibrates lumenal and cytosolic pH, in polarized MDCK cells and examined the consequences on the targeting and delivery of apical and basolateral proteins. M2 activity affects the pH of only a subset of acidified organelles, and its activity can be rapidly reversed using ion channel blockers (Henkel, J.R., G. Apodaca, Y. Altschuler, S. Hardy, and O.A. Weisz. 1998. Mol. Biol. Cell. 8:2477-2490; Henkel, J.R., J.L. Popovich, G.A. Gibson, S.C. Watkins, and O.A. Weisz. 1999. J. Biol. Chem. 274:9854-9860). M2 expression significantly decreased the kinetics of cell surface delivery of the apical membrane protein influenza hemagglutinin, but not of the basolaterally delivered polymeric immunoglobulin receptor. Similarly, the kinetics of apical secretion of a soluble form of gamma-glutamyltranspeptidase were reduced with no effect on the basolaterally secreted fraction. Interestingly, M2 activity had no effect on the rate of secretion of a nonglycosylated protein (human growth hormone [hGH]) that was secreted equally from both surfaces. However, M2 slowed apical secretion of a glycosylated mutant of hGH that was secreted predominantly apically. Our results suggest a role for acidic trans-Golgi network pH in signal-mediated loading of apical cargo into forming vesicles.

Responses of salivary acinar cells to intracellular alkalinization

Responses of rat submandibular acini to intracellular alkalinization were investigated. Intracellular alkalinization was induced by addition of NH4Cl or methyl amines, or by prepulse with Na butyrate. Only partial recovery occurred following Na butyrate prepulse or methylated amine addition, but full recovery was observed following addition of NH4Cl. The latter recovery was DIDS and dimethylamiloride-insensitive but was inhibited by bumetanide or high [K+] and stimulated in Na(+)-free buffer and by ouabain. Acetylcholine stimulated recovery from NH4Cl- or Na butyrate pre-pulse-induced alkalinization and reduced the extent of alkalinization induced by methylated amines. Acetylcholine-stimulated recovery from NH4Cl-induced alkalinization was mimicked by substance P or ionomycin and was partially Ca(2+)-dependent. This stimulated recovery was bumetanide-insensitive but was partially sensitive to charybdotoxin. Taken together, these data indicate that in unstimulated cells, recovery from alkalinization induced by NH4Cl occurs by bumetanide-sensitive transport of the NH4+ ion, that DIDS-inhibitable anion transport contributes little to this recovery, and that acetylcholine and other Ca(2+)-elevating agents accelerate recovery from NH4Cl-induced alkaline challenge by a mechanism insensitive to bumetanide, DIDS, ouabain, and dimethylamiloride but sensitive to extracellular Ca2+ and to charybdotoxin. Partial recovery from alkaline challenge can also occur in the absence of NH4+ ions, and acetylcholine also stimulates this mode of recovery. Together, these data suggest that these cells have little intrinsic ability to recover from intracellular alkalinization and that the NH4+ ion may be a surrogate for K+ in at least two ion transport pathways.