The influence of the chloride gradient across red cell membranes on sodium and potassium movements

Abstract

SUMMARY1. A study has been made to see whether active and passive movements of sodium and potassium in human red blood cells are influenced by changing the chloride gradient and hence the potential difference across the cell membrane.2. Chloride distribution was measured between red cells and isotonic solutions with a range of concentrations of chloride and non-penetrating anions (EDTA, citrate, gluconate). The cell chloride concentration was greater than that outside with low external chloride, suggesting that the sign of the membrane potential was reversed. The chloride ratio (internal/ external) was approximately equal to the inverse of the hydrogen ion ratio at normal and low external chloride, and inversely proportional to external pH. These results show that chloride is passively distributed, making it valid to calculate the membrane potential from the chloride ratio.3. Ouabain-sensitive (pump) potassium influx and sodium efflux were decreased by not more than 20 and 40 % respectively on reversing the chloride gradient, corresponding to a change in membrane potential from -9 to +30 mV. In contrast, passive (ouabain-insensitive) movements were reversibly altered -potassium influx was decreased about 60 % and potassium efflux was increased some tenfold. Sodium influx was unaffected by the nature of the anion and depended only on the external sodium concentration, whereas ouabain-insensitive sodium efflux was increased about threefold. When external sodium was replaced by potassium there was a decrease in ouabain-insensitive sodium efflux with normal chloride, but an increase in low-chloride medium.4. Net movements of sodium and potassium were roughly in accord with the unidirectional fluxes.5. The results suggest that reversing the chloride

Mechanism of the increase in cation permeability of human erythrocytes in low-chloride media. Involvement of the anion transport protein capnophorin.

“…The Gardos effect involves Ca 2+ and specifically increases K+ and Rb+ permeabilty (Gardos, 1956;Lew, 1974;Romero, 1976). In contrast, the low-Cl,, leak can be observed in the presence of the Ca 2+ chelator EDTA (Cotterrell and Whittam, 1971) and allows the passage of Na', as well as K+ and Rb+.…”

Influence of loop diuretics and anions on passive potassium influx into human red cells.

“…Unlike the' other anions tested, gluconate is impermeable and this causes the membrane potential (Em) to be reversed to inside positive (Cotterrell &;Whittam, 1971). Despite the opposing Em, gluconate increases the piretanide-insensitive influx (Fig.…”

“…The effects of five different anion substitutions on passive K influx were examined in the presence and absence of piretanide (Table 6). Amongst the anions tested, NO , SCN and I are interesting because Funder & Wieth (1967) studied them previously, SO4 and SCN because they are commonly employed in work on plasma membrane vesicles, and gluconate because it is impermeable and has been useful in work on r.b.c.s and Madin-Darby canine kidney (MDCK) cells (Cotterrell & Whittam, 1971;McRoberts, Erlinger, Rindler & Saier, 1982). except S04 (see below), 8 mM-KCl (or NO3 etc., except S04), 10 mM-glucose, 10 mM-Tris-MOPS pH 7-5, 0-1 mM-ouabain and 1-6 ,Ci 86Rb ml-' plus 10-4 M-piretanide as shown.…”

Characterization of the electrogenic sodium pump in cardiac Purkinje fibres

“…The Na pump rate has been shown to be independent of membrane potential in a variety of tissues including the squid giant axon (Hodgkin & Keynes, 1955;Brinley & Mullins, 1974), skeletal muscle (Beauge & Sjodin, 1976), red blood cells (Cotterrell & Whittam, 1971), mammalian C fibres (Den Hertog, 1973) and the giant neurones of Helix Aspersa (Lambert, Kerkut & Walker, 1974) and Anisodoris (Marmor, 1971). We have shown that, in the Purkinje fibre, stimulation of the Na pump by Rb or Cs simply lifts the I-V relationship on the current axis.…”