An investigation of the ionic mechanism of intracellular pH regulation in mouse soleus muscle fibres

• Published in: The Journal of physiology 1977-12, Vol.273 (1), p.295-316
• Main Authors: Aickin, C. Claire, Thomas, R. C.
• Format: Article
• Language: English
• Subjects: Amiloride - pharmacology; Animals; Biological Transport, Active - drug effects; Calcium - pharmacology; Carbon Dioxide - pharmacology; Hydrogen-Ion Concentration; In Vitro Techniques; Intracellular Fluid - metabolism; Mice; Muscles - cytology; Muscles - metabolism; Ouabain - pharmacology; Potassium - pharmacology; Sodium - metabolism; Sodium - pharmacology; Temperature
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1977.sp012095

1. Intracellular pH (pH i ) of surface fibres of the mouse soleus muscle was measured in vitro by recessed-tip pH-sensitive micro-electrodes. pH i was displaced in an acid direction by removal of external (NH 4 ) 2 SO 4 after a short exposure, and the mechanism of recovery from this acidification was investigated. 2. Removal of external K caused a very slow acidification (probably due to the decreasing Na gradient) but had no effect on the rate of pH i recovery following acidification. This indicates that K + —H + exchange is not involved in the pH i regulating system. 3. Short applications of 10 -4 M ouabain had no obvious effect on pH i and did not alter the rate of pH i recovery following acidification. This suggests that there is no direct connexion between the regulation of pH i and the Na pump. 4. Reduction of external Ca from 10 to 1 m M caused a transient fall in pH i , but the rate of pH i recovery following acidification was unaffected. This suggests that Ca 2+ —H + exchange is not involved in the pH i regulating system. 5. An 11% reduction in external Na caused a significant slowing of pH i recovery following acidification. 90% or complete removal of external Na almost stopped pH i recovery. This suggests that Na + —H + exchange is involved in pH i regulation. 6. Amiloride (10 -4 M ) reversibly reduced the rate of pH i recovery to much the same extent as removal of external Na. Its effect was not additive to that of removal of external Na. 7. Internal Na ion concentration ([Na + ] i ), measured using Na + -sensitive micro-electrodes, fell on application of (NH 4 ) 2 SO 4 and increased on its removal. The increase transiently raised [Na + ] i above the level recorded before (NH 4 ) 2 SO 4 application. This overshoot of [Na + ] i was almost completely inhibited by amiloride. This is consistent with the involvement of Na + —H + exchange in the pH i regulating system. 8. Removal of external CO 2 or application of SITS (10 -4 M ) caused some slowing of the rate of pH i recovery following acidification by removal of (NH 4 ) 2 SO 4 . The effect of SITS was additive to that of Na-free Ringer or amiloride. These results suggest that Cl - —HCO 3 - exchange is also involved in the pH i regulating system and that it is a separate mechanism. Under the conditions used, Cl - —HCO 3 - exchange formed about 20% of the pH i regulating system. 9. Decreasing the temperature from 37 to 28 °C not only caused an increase in pH i , but also considerably sl