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The distribution of small ions during the early development of Xenopus laevis and Ambystoma mexicanum embryos.
Author(s) -
Gillespie J I
Publication year - 1983
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1983.sp014945
Subject(s) - blastula , intracellular , xenopus , embryo , neurula , gastrulation , biophysics , biology , neurulation , anatomy , embryogenesis , chemistry , microbiology and biotechnology , biochemistry , gene
The free ion concentrations of Na+, K+ and Cl‐ have been measured in the cells and intercellular spaces of developing amphibian embryos using ion‐sensitive microelectrodes. Ca2+, H+ and buffering capacity have also been measured in the intercellular spaces. The free intracellular Na+ and K+ concentrations in the early cleavage stages remain approximately constant at 21 mM and 90 mM respectively. The free intracellular Cl‐ concentration, approximately 60 mM during the egg to 4‐cell stage, falls during development to around 30 mM by the 128‐cell stage. Embryos from different batches show a wide variation in intracellular free ion content. A strong correlation was observed between the ion content, particularly of K+, and the viability of the embryo. If the intracellular K+ concentration was less than 60 mM, embryos invariably died between late blastula and early gastrula stages; if greater than 80 mM the embryo generally survived. The intercellular free Na+, K+, Cl‐ and Ca2+ concentrations in Xenopus mid‐blastula embryos are 91 mM, 4 mM, 59 mM and 1.5 mM respectively. The intercellular potential at late neurula stages is +3.5 mV when the embryo is bathed in 5% Ringer solution; changing to Ringer solution reduced the potential to ‐4 mV. Before gastrulation the intercellular Ca2+ concentration in Xenopus falls to approximately 0.5 mM, where it remains throughout gastrulation before returning to its mid‐blastula value during neurulation. In Xenopus, the intercellular Na+ concentration falls to around 75 mM and the intercellular K+ concentration rises to around 17 mM at the end of gastrulation. These changes are not maintained and both Na+ and K+ concentrations return to their earlier values. In Ambystoma, the intercellular K+ concentration falls steadily from 7 mM at the mid‐blastula stage to 2 mM at the end of neurulation. The Na+ concentration is constant at approximately 93 mM up to stage 14; between stages 14 and 16 the measurements show some scatter (minimum value 60 mM, maximum value 100 mM), and beyond stage 16 the Na+ concentration increases to 123 mM.