Volume-regulatory responses of Amphiuma red cells in anisotonic media. The effect of amiloride

• Published in: The Journal of general physiology Vol. 86; no. 4; pp. 527 - 564
• Main Authors: SIEBENS, A. W, KREGENOW, F. M
• Format: Journal Article
• Language: English
• Published: New York, NY Rockefeller University Press 01.10.1985; The Rockefeller University Press
• Subjects: amiloride; Amiloride - pharmacology; Amphiuma; Animals; Biological and medical sciences; Cell physiology; Culture Media; erythrocytes; Erythrocytes - drug effects; Erythrocytes - physiology; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Kinetics; Miscellaneous; Molecular and cellular biology; Osmolar Concentration; Ouabain - pharmacology; potassium; Potassium - blood; sodium; Sodium - blood; Urodela; Vertebrata; Blood cell; Regulation(control); Volume; Amphibia; Red blood cell; Osmotic pressure
• ISSN: 0022-1295; 1540-7748
• DOI: 10.1085/jgp.86.4.527

Amphiuma red cells were incubated for several hours in hypotonic or hypertonic media. They regulate their volume in both media by using ouabain-insensitive salt transport mechanisms. After initially enlarging osmotically, cells in hypotonic media return toward their original size by losing K, Cl, and H2O. During this volume-regulatory decrease (VRD) response, K loss results from a greater than 10-fold increase in K efflux. Cells in hypertonic media initially shrink osmotically, but then return toward their original volume by gaining Na, Cl, and H2O. The volume-regulatory increase (VRI) response involves a large (greater than 100-fold) increase in Na uptake that is entirely blocked by the diuretic amiloride (10(-3) M). Na transport in the VRI response shares many of the characteristics of amiloride-sensitive transport in epithelia: (a) amiloride inhibition is reversible; (b) removal of amiloride from cells pretreated with amiloride enhances Na uptake relative to untreated controls; (c) amiloride appears to act as a competitive inhibitor (Ki = 1-3 microM) of Na uptake; (d) Na uptake is a saturable function of external Na (Km approximately 29 mM); (e) Li can substitute for Na but K cannot. Anomalous Na/K pump behavior is observed in both the VRD and the VRI responses. In the VRD response, pump activity increases 3-fold despite a decrease in intracellular Na concentration, while in the VRI response, a 10-fold increase in pump activity is observed when only a doubling is predicted from increases in intracellular Na.