AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 542-R548, Copyright © 1994 by American Physiological Society
Control of red cell function of late chick embryos: role of extracellular ATP/AMP and egg size
M. Koller, S. Dragon and R. Baumann
Physiologisches Institut, Universitat Regensburg, Germany.
Hypoxia is the alleged stimulus for initiation of increase of carbonic
anhydrase II (CAII) and 2,3-diphosphoglycerate (2,3-DPG) synthesis of red
blood cells from late chick embryos. The PO2-dependent regulation of red
cell metabolism is mediated by unknown humoral factors [Million et al., Am.
J. Physiol. 261 (Regulatory Integrative Comp. Physiol. 30): R1188-R1196,
1991]. In the present investigation we have analyzed whether
interindividual differences in egg size (which result in different surface
area-to-mass ratios) affect the timing of initiation of 2,3-DPG and CAII
synthesis in late chick embryos. We also investigated the effect of
extracellular adenine nucleotides on red cell organic phosphate pattern and
O2 affinity to test whether the inhibitory effect of normal or elevated PO2
on 2,3-DPG synthesis and the concomitant increase of ATP (and O2
half-saturation pressure) can be mimicked by these agents. The results show
that differences in egg size affect the timing of CAII and 2,3-DPG
synthesis, indicating that PO2-dependent regulation of red cell function
allows adjustment to the properties of the individual egg. We also found
that extracellular ATP, which is rapidly degraded to AMP by red cell
ectoenzymes, can alter the red cell phosphate pattern and O2 affinity,
i.e., significantly increase red cell ATP, decrease red cell 2,3-DPG and O2
affinity, and thus mimic the effect of normoxia and hyperoxia. These
findings suggest that extracellular adenine nucleotides may be involved in
the PO2-dependent regulation of embryonic red cell metabolism.
