Intracellular pH of Rat Atrial Muscle Fibers Measured by Glass Micropipette Electrodes

Measurements of the intracellular pH of mammalian hearts by means of ordinary sealed electrodes are difficult mainly because of the small diameter of most of these muscle fibres. An open-tip pH micro-electrode was designed. The difference between the measurements with this electrode and measurements with a control pyrex glass electrode of the same resistance, filled with the same medium, and immersed in the same solution, is specific for the pH variations of this solution. The new pH electrode, if filled with 0.5 M KCl, has an electrical resistance of 30 to 100 megohms and a sensitivity of about 30 mv/pH unit. The sensitive head of the device has a diameter of about half a micron and a length of one to two microns. The intracellular pH value of isolated rat atria, beating at 200/min in a Krebs-Ringer solution maintained at 30°C and at a pH value of 7.4, was measured with this method and found to be 6.9.