The effects of CO 2 and pH on the spontaneous activity of the Taenia coli of guinea-pig.

Abstract

Mechanical and electrical activity of the isolated guinea-pig taenia coli were recorded in bicarbonate-, Tris- or phosphate-buffered test solutions. In normal solution (pCO2 5%, pH 7.4), typical minute-rhythmical fluctuations of activity occurred, whereby activity was present for approximately 40% of the total time (active time), the other 60% being activity-free intervals. At constant extracellular pH, low CO2 content increased active time, high CO2 content reduced it. Extracellular alkalinization at constantpCO2 also diminished active time, even in CO2-free medium, whereas acidification raised it, sometimes causing continuous activity. At constant bicarbonate-buffer, changes of CO2 content, i.e. accompanied by corresponding changes in pH, affected the active time much less than did CO2 alterations in an isohydric medium. The test solutions had no major effect on frequency of synchronized spike discharges, in contrast to their actions on the minuterhythmical activity. Since CO2 can pass through the cell membrane more easily than ions regulating intra- and extracellular pH, the observed effects are best explained by changes in the transmembrane pH-gradient. A drop in active time would be due to a relative intracellular acidification; continuous activity, on the other hand, due to an opposite change in transmembrane pH-gradient, i.e. a relative intracellular alkalinization.