The effect of pH on the respiration of brain tissue; the pH of tissue slices.

With slices of various guinea pig tissues suspended in bicarbonate-free horse serum adjusted to various pH values, Canzanelli et al. (1) found that maximum rates of oxygen uptake occurred in all cases in media with pH values well above 7.4. With brain slices, the curve relating respiration rate to the pH of the medium rose with increasing pH, rapidly up’to pH 6, less rapidly from 6 to 8, and then rapidly again to give a marked maximum at pH 9 to 9.5. It finally fell sharply with further increase in pH. Canzanelli et al. summarized previous work on the effects of pH on tissue respiration. Much of it was unsatisfactory with regard to pH control and measurement and for other reasons. The surprisingly high optimum found by Canzanelli et al. suggested that the question should be studied further. As a result of the studies here reported we conclude that the true optimum pH for the respiration of brain tissue is in the usual physiological range and that the actual pH within slices is usually appreciably different from that of the medium in which they are immersed.