31P NMR reveals increased intracellular pH after fertilization in Xenopus eggs.

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Abstract
31P NMR spectra of mature eggs of the frog (X. laevis) were taken prior to and after both fertilization and activation by a Ca2+/H+ ionophore (A23187; calcemycin). The eggs were constantly perfused with fresh well-buffered solution during the experiments and the intracellular pH (pHi) was determined from the pH-dependent chemical shift of the internal Pi peak. The detection of this Pi peak in the presence of overlapping yolk phosphoprotein signals was accomplished by a T2 experiment which discriminated against the broader yolk phosphoprotein peak. The average pHi of the unfertilized, fertilized and activated eggs was 7.42, 7.66 and 7.64, respectively. A cytoplasmic alkalinization of 0.24 pH unit occurs within 90 min after fertilization. These values are practically identical to pHi measurements made in this laboratory on Xenopus eggs by using pH-sensitive glass microelectrodes. Extracellular pH changes as large as 3 pH units had no effect on pHi. Phosphocreatine levels are very sensitive to metabolic pertubations such as O2 depletion or metabolic inhibitor application. These treatments resulted in a rapid decrease in the phosphocreatine concentration; the ATP concentration declined only slowly after the phosphocreatine peak had disappeared.