Developmental changes in the management of acid loads during preimplantation mouse development.
Intracellular pH recovery in Quackenbush Swiss mouse preimplantation embryos following acid loading was investigated under conditions of H+-monocarboxylate cotransporter inactivity. Isoform-sensitive inhibitors of Na+-H+ exchange (NHE) were used to block the Na+-dependent component of the response. A biphasic dose-response curve for HOE-694 and N-methylisopropylamiloride (MIA) suggested that two isoforms (putatively NHE1 and NHE3) are active in the oocyte, 1-cell, and 2-cell stages. By the blastocyst stage, loss of one of the MIA-sensitive NHE activities (putatively NHE3) was observed in isolated inner cell masses, and an MIA-resistant component of the recovery was identified. The MIA-resistant component was inhibited by 2 mM amiloride and enhanced by external K+ and by 4,4'-diisothiocyanostilbene-2,2'-disulfonate, suggesting NHE4 activity. However, unlike NHE4 in other tissues, the MIA-resistant component did not transport Li+ in exchange for H+, and reverse transcription-polymerase chain reaction detected NHE4 mRNA in the oocyte but not in later stages. Trophoblast, whether in intact or collapsed blastocysts, did not show measurable NHE activity or MIA-sensitive activity during recovery from acid load. Both trophoblast and pluriblast manifested an H+ conductance in response to acid load. This H+ conductance was first detected at the 8-cell stage and was blocked by zinc in the isolated inner cell mass but not in trophoblast. No other effective inhibitors of its activity were found.
Harding
E A
EA
Department of Physiology, University of Sydney, New South Wales 2006, Australia.
Gibb
C A
CA
Johnson
M H
MH
Cook
D I
DI
Day
M L
ML
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000143:Acids / Q000378:metabolism*; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001755:Blastocyst / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D006146:Guanidines / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008094:Lithium / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D011247:Pregnancy; D020033:Protein Isoforms / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D014327:Trophoblasts / Q000187:drug effects / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
D000143:Acids; D006146:Guanidines; D020033:Protein Isoforms; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C048793:methylisopropylamiloride; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; D000584:Amiloride; D006859:Hydrogen; D008094:Lithium; D015032:Zinc; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid