title: Volume-regulatory responses of Amphiuma red cells in anisotonic media. The effect of amiloride.
abstract: 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.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D003470:Culture Media; D004912:Erythrocytes / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood; D014562:Caudata
chemical_list: D003470:Culture Media; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D011188:Potassium