Effect of pH alteration on growth and glucose oxidation in myoblast cultures

The growth of chick heart cells in culture declines when the cells reach confluency. The decline in growth rate is associated with both a decrease in the pH of the bicarbonate-CO₂ buffered medium and a reduced capacity for glucose oxidation by the pentose phosphate pathway. The pH of proliferating cultures supplemented with either 14 mM NaHCO₃ or with a mixture of organic buffers (pK 7.4) was increased by 0.3 pH unit over that of the controls. The rate of glucose oxidation by the pentose phosphate pathway in confluent cultures supplemented with NaHCO₃ or organic buffer increased by 60% 24 h after pH correction. This was associated with an increase in glucose uptake from the medium. We conclude that pH elevation in confluent heart cell cultures stimulates both growth and the capacity for glucose oxidation by the pentose phosphate pathway. The data also provide further evidence for a relationship between activity of the pentose phosphate pathway and cell growth.