The use of microelectrodes for measurement of local H+ activity in the cortical subarachnoidal space of cats

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Abstract
Summary pH microelectrodes with pointed tip (Hinketype) were constructed for the continuous measurement of the local pH in the perivascular space of pial arteries in the feline cerebral cortex. The sensitive tip had a length of 20–60 μ and a base diameter of 10–25 μ. As reference electrode, a micropipette (tip diameter 2 μ), filled with 150 mM KCl was used. Calibration curves were linear and showed a sensitivity of 54.5–57.5 mV/pH unit at 38°C. Advantages of such electrodes are the easy penetration of the subarachnoid membrane, the long life span, the quick response, and a minimal drift.—The electrodes were tested in vivo during hyper- and hypoventilation and during local perivascular injection of mock spinal fluid at varying pH. A close correlation was observed between the change in perivascular pH and the corresponding change in pial arterial diameter.