title: Evidence that a Na+/Ca2+ antiport system regulates murine erythroleukemia cell differentiation.
abstract: The Na+ and Ca2+ transport properties of cultured murine erythroleukemia (MEL) cells have been investigated. We have previously shown that amiloride prevents dimethyl sulfoxide-induced MEL cell differentiation via inhibition of an essential Ca2+ influx (levenson, R., Housman, D., and Cantley, L. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 5948-5952). Here we show that external Na+ inhibits Ca2+ influx and stimulates Ca2+ efflux from uninduced MEL cells. Increasing the internal Na+ concentration by a brief incubation of cells with ouabain stimulates the rate of 45Ca2+ influx. Amiloride (40 microM) completely blocks the external Na+-stimulated 45Ca2+ efflux and external Na+-inhibitable 45Ca2+ influx. The same concentration of amiloride had no significant effect on net Na+ uptake. These results suggest that a significant fraction of Ca2+ flux across the MEL cell plasma membrane occurs via a Na+/Ca2+ antiport system and that amiloride prevents differentiation by blocking Ca2+ influx through this system. The importance of a Na+/Ca2+ antiport system for MEL cell differentiation is supported by the following observation: increasing the cellular Na+ level by a brief treatment with ouabain plus monensin accelerates MEL cell commitment as effectively as adding the Ca2+ ionophore A23187. We suggest that dimethyl sulfoxide induces MEL cell differentiation by inhibiting the Na+ pump and consequently allowing Ca2+ influx through the Na+/Ca2+ antiport.
mesh_terms: D000584:Amiloride / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology*; D002454:Cell Differentiation; D007700:Kinetics; D007942:Leukemia, Experimental / Q000503:physiopathology*; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008985:Monensin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D012413:Rubidium; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D019831:Sodium-Calcium Exchanger; D010042:Ouabain; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D012413:Rubidium; D002118:Calcium