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We describe a new method for calibrating intracellular pH (pH1) measurements by flow cytometry, based on the null point method proposed originally by Eisner et al. (Pflügers Arch 413:553-558, 1989). The method involves suspending cells loaded with pH-sensitive dyes, such as SNARF-1 or BCECF, in defined mixtures of the weak acid butyric acid and the weak base trimethylamine. Only the uncharged forms of these agents freely permeate the plasma membrane. The weak acid donates protons intracellularly, whereas the weak base accepts them. In accordance with the Henderson-Hasselbalch equation, when cells are exposed to these mixtures, the steady-state pHi is displaced, and the fluorescence signal reflects this new pHi. The null point method described by Eisner et al. derives pHi by determining the molar ratio of acid to base that produces no change in fluorescence signal. In this paper, we show that it is not necessary to obtain the true null point, because a calibration curve can be derived from "pseudo null" values whose pHi is defined by the equation pHi = pHe -0.5 log [(AT)/(BT)], where pHe is the extracellular pH, and (AT) and (BT) are the total concentrations of weak acid and base in the suspension. We refer to this as the "pseudo null calibration method." It is rapid, technically simple, and reproducible. Compared with the widely used nigericin calibration method, it is not influenced by the intracellular potassium concentration; therefore, it may give a more reliable estimate of the absolute value of pHi.

The present study was designed to assess the preferred methods of treatment of breast cancer by American oncologists, and the impact of clinical trials on their practice. We mailed 465 questionnaires to surgical, radiation, or medical oncologists. The questionnaire described five hypothetic patients with breast cancer, and respondents were asked to select their preferred treatment for each patient. For primary breast cancer, most physicians would offer the choice of local excision followed by radiation therapy or modified radical mastectomy. About 80% of physicians would prescribe adjuvant chemotherapy for a premenopausal woman with estrogen receptor-negative, axillary node negative breast cancer, and for a postmenopausal woman with estrogen receptor-negative, node-positive disease. This policy was favored by male and female physicians of each specialty. Almost all respondents would treat a young woman with inflammatory breast cancer with initial chemotherapy followed by radiation and/or surgery, and about 60% would recommend chemotherapy to a postmenopausal patient with estrogen receptor-negative disease and minimally symptomatic bone metastases. Clinical trials have compared treatment strategies that could be applied to patients described in our questionnaire. Preferred treatments for primary breast cancer, and for inflammatory breast cancer are supported by the results of clinical trials. Recommendation of adjuvant chemotherapy for node-negative breast cancer is not based on a consistent demonstration of improvement in survival, although randomized trials with short follow-up have shown delay to recurrence. Recommendation of adjuvant chemotherapy for a postmenopausal woman with node-positive breast cancer is contrary to the results of large randomized controlled trials (and to a meta-analysis), which have shown that this policy does not lead to improved survival. Our report suggests that even large randomized clinical trials may have a minimal impact on practice if their results run counter to belief in the value of the treatment.

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