pH distributions in transplanted neural tumors and normal tissues of BDIX rats as measured with pH microelectrodes.

The distribution of pH values was measured in transplanted neuroectodermal TV1A tumors and in brain and kidney of BDIX rats in vivo. Tissue damage during pH measurements could be minimized by the use of Hinke-type pH glass microelectrodes with maximum diameters of the pH-sensitive tips of less than or equal to 10 micrometers (sensitivity, 58 to 60 mV/pH unit at 37 degrees; response time (95%), less than or equal to 3 sec; drift, less than or equal to 0.01 pH unit/hr). The advantages and limitations of this technique are discussed in relation to other methods for the analysis of extracellular pH. In tumors weighing 1.0 to 2.5 g, pH values ranged from 6.8 to 7.1 (mean, 7.0). The pH distribution in tumors weighing 4 to 6 g was shifted to slightly lower values, with an average pH of 6.9 (range, 6.7 to 7.1). No marked pH differences were found between the tumors and normal tissues. The pH values measured in brain and kidney ranged from 6.6 to 7.3 (mean, 7.0) and 6.7 to 7.3 (mean, 7.1), respectively. Within single tumors, local pH variations in the range of 0.2 to 0.3 pH unit were observed. The local pH values measured in certain tumor areas are, however, sufficiently low to partially inhibit proliferation and colony formation in cultured malignant cells.