PubMed · 13358
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H F Rittel, E Waterloh, K Rössmann, F A Schön. 1977. [Computers in lung function tests (author's transl)].. https://pubmed.ncbi.nlm.nih.gov/13358/
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As was shown in our previous work, the intracellular pH (pHi) of cultured human fibroblasts depends on cell density. The pHi is low in single cells, higher in cells, forming small groups and maximal in a sparse monolayer. On the other hand, the pHi is low in areas of confluent monolayers. In the present work, we show that the effects of inhibitors of various pH-controlling mechanisms as well as inhibitors of key enzymes in signal transduction pathways depend on the local cell density. We have found that N-ethylmaleimide and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, known as inhibitors of V-type H+ ATPase, inhibit the elevation of pHi induced by cell-cell contact interactions; meanwhile Cd2+ ions, which inhibit H+ conductive pathway, cause an increase of pHi in a confluent monolayer. Our data revealed also that the Na+/H+ antiporter does not play an essential role in the pHi regulation by intercellular contacts. Inhibitors of phospholipase A2 (4-bromophenacyl-bromide), phospholipase C (neomycin) and protein kinase C (H-7) dramatically change the way the pHi is modulated by local cell density. It is suggested that cell-cell interactions regulate cell activities via modulation of pHi, which is under positive control from phospholipase A2 and under negative control from protein kinase C.
METHOD: Eighteen hospitalized patients with candiduria were treated with oral potassium-sodium-hydrogen citrate to alkalinize the urine. The results obtained were compared with those observed in an untreated retrospective control group. Dosage was adjusted in accordance with the pH of the urine measured immediately before treatment with the aim of achieving a pH of 7 to 7.5. RESULTS: All patients had an indwelling catheter, which is a predisposing factor for candiduria. In 16 out of 18 patients (89%) treatment with potassium-sodium-hydrogen citrate raised pH and resulted in the disappearance of candiduria. Duration of treatment varied between two days and one month (mean: seven days). In four patients the urine became completely sterile; during treatment 12 out of 18 patients developed significant bacteriuria (in eight cases of these the indwelling catheter had been left in place). CONCLUSIONS: Alkalinization of the urine is a simple and effective method of treating candiduria in patients with an indwelling catheter. An additional advantage is the metaphylaxis and prophylaxis of renal stone formation in immobilized patients.
An acid-base chemical mechanism is proposed for Hafnia alvei aspartase in which a proton is abstracted from C-3 of the monoanionic form of L-aspartate by an enzyme general base with a pK of 6.3-6.6 in the absence and presence of Mg2+. The resulting carbanion is presumably stabilized by delocalization of electrons into the beta-carboxyl with the assistance of a protonated enzyme group in the vicinity of the beta-carboxyl. Ammonia is then expelled with the assistance of a general acid group that traps an initially expelled NH3 as the final NH4+ product. In agreement with the function of the general acid group, potassium, an analog of NH4+, binds optimally when the group is unprotonated. The pK for the general acid is about 7 in the absence of Mg2+, but is increased by about a pH unit in the presence of Mg2+. Since the same pK values are observed in the pKi(succinate) and V/K pH profile, both enzyme groups must be in their optimum protonation state for efficient binding of reactant in the presence of Mg2+. At the end of a catalytic cycle, both the general base and general acid groups are in a protonation state opposite that in which they started when aspartate was bound. The presence of Mg2+ causes a pH-dependent activation of aspartase exhibited as a partial change in the V and V/Kasp pH profiles. When the aspartase reaction is run in D2O to greater than 50% completion no deuterium is found in the remaining aspartate, indicating that the site is inaccessible to solvent during the catalytic cycle.