Erythrocytes possess a Cl-dependent, Na-independent K transport system cotransporting K and Cl in a 1:1 stoichiometry that is membrane potential independent. This K-Cl cotransporter is stimulated by cell swelling, acidification, Mg depletion, and thiol modification. Cell shrinkage, elevation of cellular divalent ions, thiol alkylation, phosphatase inhibitors, and derivatives of certain loop diuretics and stilbenes are inhibitory. Thus regulation of K-Cl cotransport at the membrane and cytoplasmic levels is highly complex. Basal K-Cl cotransport decreases with cellular maturation, whereas its modes of stimulation and inhibition are variable between species. The physiological inactivation appears to be prevented in low-K animal erythrocytes. In certain human hemoglobinopathies, K-Cl cotransport may be the cause of cellular dehydration and volume decrease. K-Cl cotransport occurs also in nonerythroid cells, such as in epithelial and liver cells of other species. At the threshold of molecular characterization, this comprehensive review places our present understanding of the mechanisms modulating K-Cl cotransport physiologically and pathophysiologically into kinetic and thermodynamic perspectives.

This is the first report describing cell movements of a repetitive character during hypotonic lysis of erythrocytes (haemolysis). A new, simply constructed chamber is described for microscopy of freely suspended cells, for example, blood cells, during the inflow of a new medium. Hypotonic haemolysis of individual red blood cells was studied. During the first phase of haemolysis discontinuities were found: the cells made between zero and seven sudden movements or ‘jumps’, interpreted as caused by an ejection of cytoplasm due to excess intracellular hydraulic pressure and the formation of a hole. After pressure equilibration the hole resealed spontaneously. When, after one or two jumps, the inflow of hypotonic medium was stopped, the haemolytic process was interrupted but continued after restarting the flow. Inhibition of haemoglobin (Hb) release by 80% by external Ficoll® did not affect the number of ‘jumps’. Since the optical contrast was reduced owing to Hb release after the last jump, less than 20% of the Hb loss can be associated with the jumps. Ejections of faint clouds of Hb were observed mainly in the presence of Ficoll®, but only after the last jump.

Recently we proposed that cytoplasmic acidification of low K+ (LK) sheep erythrocytes may stimulate ouabain-resistant Cl(-)-dependent K+ flux (K+: Cl- contransport), also known to be activated by cell swelling, treatment with N-ethylmaleimide (NEM), or removal of cellular bivalent cations. Here we studied the dependence of K+ transport on intracellular and extracellular pH (pHi, pHo) varied either simultaneously or independently using the Cl-/HCO3- exchange inhibitor 4,4, diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). In both control and NEM-treated LK cells volumes were kept near normal by varying extracellular sucrose. Using DIDS as an effective pH clamp, both K+ efflux and influx of Rb+ used as K+ congener were strongly activated at acid pHi and alkaline pHo. A small stimulation of K+ (Rb+) flux was also seen at acid pHi in the absence of DIDS, i.e., when pHi approximately pHo. Anti-Ll serum, known to inhibit K+: Cl-cotransport, prevented the pHi-stimulated K+ (Rb+) fluxes. Subsequent to NEM treatment at pH 6, K+ (Rb+) fluxes were activated only by raising pH, and thus were similar to the pH activation profile of K+ (Rb+) fluxes in DIDS-treated cells with pHo varied at constant physiologic pHi. Anti-Ll, which inhibited NEM-stimulated K+ (Rb+) fluxes, failed to do so in NEM-plus DIDS-treated cells. Thus, NEM treatment interferes with the internal but not with the external pH-sensitive site.

Three neutral polymers, ficoll, dextran and polyethyleneglycol, all inhibit hemoglobin liberation in hypotonic electrolyte solutions. If red cells are suspended in a hypotonic solution which, in the absence of a polymer, would hemolyse all the cells, only a part of the hemoglobin is liberated. The polymer does not alter the fragility but only the amount of hemoglobin liberated from the individual cells. The inhibitory effect is proportional to the weight concentration of the polymer and independent of the mol. wt. within wide limits. The inhibitor molecules must presumably have a critical minimal size since the trisaccharide raffinose did not inhibit hemoglobin liberation under similar conditions. From the data on the lowest molecular weight dextran fraction it was concluded that the lower limit for dextran was below a molecular weight of about 1700. Complete inhibition of hemoglobin liberation was never obtained and from the evidence available it is suggested that the first 20 per cent, at least, of the hemoglobin may escape with a bulk outflow. The colloid osmotic relationships of the cell during and after hemolysis are discussed and it is concluded that cannot be decided whether the polymer effect is colloid osmotic in nature.