pH Heterogeneity in Skeletal Muscle Extracellular Fluid

Abstract

Oxygen and carbon dioxide are known to be heterogeneously distributed in tissues. Extracellular skeletal muscle tissue pH (pH_t) also exhibits a spatial variability in vitro, but this has not been examined in vivo. pH_t distributions in resting skeletal muscle and the effect of the dispersion of pH_t on ischemia and normoxic hypercarbia was therefore studied in an animal model with a multichannel pH microelectrode. Under resting conditions and spontaneous breathing, local pH_t (from all animals, n = 10) was found to vary between 6.96 and 7.68 (range), and 70% of the values were within a pH of 7.00-7.32. In each animal the maximum pH_t differences (maximum range between the 6 channels of the microelectrode) found were 0.32 ± 0.11 pH units (mean ± SD). During tissue acidosis, induced by ischemia, no significant change in the local pH_t differences in each animal was seen. During normoxic hypercarbia a 2-fold increase in pH_t variability within each animal was noticed (p < 0.01), which suggests that carbon dioxide and buffering effects of the blood are significant factors for the pH_t distribution. The pH_t distribution range found is of similar magnitude as previously described in in vitro studies on skeletal muscle. Locally varying pH_t levels may be of importance as they will affect cellular H⁺ extrusion, membrane potential and volume control of different cell populations differently.

Dual mode antimony electrode for simultaneous measurements of PO2 and pH

“…The pH sensitivity in the P mode was similar to that presented in several previous studies ( 7, 8, 10). At oxygen concentrations above 5% the sensitivity was characteristic.…”

“…However, this solution also did not exclude oxygen ( 9). Furthermore, in tissues during ischaemic conditions we found a normal P pH sensitivity, which suggests that the electrode corrosion process operates at extremely low oxygen tensions ( 8). This is probably a minor problem as, from a practical and clinical point of view, it is extremely unusual for oxygen to be totally absent.…”

“…The sensitivity of the antimony electrode, for both oxygen and pH, has limited the biomedical use of this sensor although the stability and reproducibility of the electrode signal for potentiometric measurements, particularly of pH, is acknowledged to be favourable when the electrode is made of COMA ( 7–10). In previous experimental models other techniques such as manipulating the oxygen tension of the preparation have been used to identify the pH component of the signal ( 8). The dual mode measurement technique (amperometric and potentiometric) allows the separation of the two parts of the composite electrode signal.…”

“…The introduction of crystallographically orientated monocrystalline antimony (COMA), by Edwall in 1978 eliminated the shortcomings resulting from drift and instability of this sensor for pH measurements ( 7). The remaining problem has been the double sensitivity of the electrode which excludes its use in the usual conditions in which both oxygen and pH vary, if the oxygen and pH components of the composite electrode signal are not separable ( 8, 9).…”

“…As a solid state sensor it has several inherent advantages that makes it interesting for biomedical applications. It is sturdy and therefore easy to miniaturise ( 8), less expensive, non‐toxic, and in the potentiometric mode has a very small oxygen consumption in the measuring area of the electrode ( 10).…”