Regulatory and energetic role of Na+ in amino acid uptake by fertilized sea urchin eggs.
Relationships between the Na+ dependent amino acid uptake displayed by fertilized sea urchin eggs and the electrochemical gradient of Na+ was investigated. The time course of Na+ content and valine or alanine uptake was simultaneously monitored in Na+ loaded eggs [by fertilization in K+-free artificial sea water (OK-ASW), or by using monensin, antimycin, cyanide, or ciguatoxin]. Our results demonstrate that the uphill amino acid uptake follows the "Na+ gradient hypothesis." Subsequent fertilization of eggs Na+ depleted by ammonia for 40 min stimulates to a great extent the development of amino acid uptake as compared with controls eggs. By using simultaneous change of external and intracellular Na+ concentration, we studied the specific role of this ion. An increase in internal Na+ inhibits the uptake through trans inhibitory action while an increase in external Na+ stimulates the efficiency of the uptake system. In eggs fertilized since 30 min, hyperpolarization obtained in K+-free ASW stimulates amino acid uptake while depolarization (transfer from K+ free ASW to ASW) inhibits it. This potential-dependent effect developed after fertilization with a time course similar to that the establishment of K+ conductance described by R. A. Steinhardt, L. Lundin, and D. Mazia (1971, Proc. Natl. Acad. Sci. USA 68, 2426-2430). In conclusion, our results point out that slight modulations in the activity of the Na+ pump can widely affect the amino acid uptake, suggesting that activation of Na+/K+ ATPase has a key role in the stimulation of amino acid transport.
D000596:Amino Acids / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D001692:Biological Transport; D002922:Ciguatoxins / Q000494:pharmacology; D005306:Fertilization; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000187:drug effects; D008564:Membrane Potentials; D008985:Monensin / Q000494:pharmacology; D010063:Ovum / Q000378:metabolism*; D011188:Potassium / Q000502:physiology; D012617:Sea Urchins / Q000196:embryology; D012964:Sodium / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology
D000596:Amino Acids; D007473:Ion Channels; D000643:Ammonium Chloride; D002922:Ciguatoxins; C032456:antimycin; D000968:Antimycin A; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium