| Abstract: | Duck red cells exhibit specific volume-sensitive ion transport processes that are inhibited by furosemide, but not by ouabain. Swelling cells in a hypotonic synthetic medium activates a chloride-dependent, but sodium-independent, potassium transport. Shrinking cells in a hypertonic synthetic medium stimulates an electrically neutral co-transport of Na + K + 2 Cl] with an associated 1:1 K/K (or K/Rb) exchange. These shrinkage-induced modes can also be activated in both hypo- and hypertonic solutions by beta-adrenergic catecholamines (e.g., norepinephrine). Freshly drawn cells spontaneously shrink approximately 4-5% when removed from the influence of endogenous plasma catecholamines, either by incubation in a catecholamine-free, plasma-like synthetic medium, or in plasma to which a beta-receptor blocking dose of propranolol has been added. This spontaneous shrinkage resembles the response of hypotonically swollen cells in that it is due to a net loss of KCl with no change in cell sodium. Norepinephrine abolishes the net potassium transport seen in both fresh and hypotonically swollen cells. Moreover, cells swollen in diluted plasma, at physiological pH and extracellular potassium, show no net loss of KCl and water ("volume-regulatory decrease") unless propranolol is added. Examination of the individual cation fluxes in the presence of catecholamines demonstrates that activation of Na + K + 2Cl] co-transport with its associated K/Rb exchange prevents, or overrides, swelling-induced K + Cl] co-transport. These results, therefore, cast doubt on whether the swelling-induced K + Cl] system can serve a volume-regulatory function under in vivo conditions. |
