Phosphomonoesters in the guinea-pig taenia caeci: pH-dependency of the phosphomonoester peaks in 31P-NMR.

In the smooth muscle of guinea-pig taenia caeci, unlike cardiac and skeletal muscles, two prominent peaks are constantly observed in the phosphomonoester (PME) region (at 6.8 and 6.3 ppm) of 31P-NMR spectra. Tissue extracts, whose pH were adjusted to the intracellular pH of 7.1, also showed such peaks. According to the pH-dependency of the chemical shifts of known PMEs, these peaks were identified as phosphorylethanolamine (PEt) and phosphorylcholine (PCh), the intermediary metabolites of membrane phospholipid turnover. In normal solution, the intracellular pH (pH(i)) which was estimated from the chemical shifts of PMEs (PEt 7.07; PCh 7.17) agreed with that from P(i) (7.10). When preparations were exposed to hypoxia and high-Mg2+ conditions, a reasonable correlation was found between estimations of pH(i) from the PME and P(i) peaks. The chemical shifts of these PME peaks may be used for estimation of pH(i), at least, when there is a need to know relative changes of pH(i), as a complementary purpose, and also whenever the P(i) peak is not clearly observed.