Role of Nitrite, a Nitric Oxide Derivative, in K-Cl Cotransport Activation of Low-Potassium Sheep Red Blood Cells

Abstract.

K-Cl cotransport (COT) is the coupled movement of K and Cl, present in most cells, associated with regulatory volume decrease, susceptible to oxidation and functionally overexpressed in sickle cell anemia. The aim of this study was to characterize the effect of the oxidant nitrite (NO₂ ⁻) on K-Cl COT. NO₂ ⁻ is a stable metabolic end product of the short-lived highly reactive free radical nitric oxide (NO), an oxidant and modulator of ion channels, and a vasodilator. In some systems, the response to NO₂ ⁻ is identical to that of NO. We hypothesized that NO₂ ⁻ activates K-Cl COT. Low potassium (LK) sheep red blood cells (SRBCs) were used as a model. The effect of various concentrations (10⁻⁶ to 10⁻¹ m) of NaNO₂ was studied on K efflux in hypotonic Cl and NO₃ media, Cl-dependent K efflux (K-Cl COT), glutathione (GSH), and methemoglobin (MetHb) formation. In support of our hypothesis, K efflux and K-Cl COT were stimulated by increasing concentrations of NaNO₂. Stimulation of K efflux was dependent upon external Cl and exhibited a lag phase, consistent with activation of K-Cl COT through a regulatory mechanism. Exposure of LK SRBCs to NaNO₂ decreased GSH, an effect characteristic of a thiol-oxidizing agent, and induced MetHb formation. K-Cl COT activity was positively correlated with Methb formation. N-ethyl-maleimide (NEM), a potent activator of K-Cl COT, was used to assess the mechanism of NO₂ ⁻ action. The results suggest that NEM and NO₂ ⁻ utilize at least one common pathway for K-Cl COT activation. Since NaNO₂ is also a well known vasodilator, the present findings suggest a role of K-Cl COT in vasodilation.