A hypothesis of the disc-sphere transformation of the erythrocytes between glass surfaces and of related observations

Erythrocytes suspended at a low hematocrit in a non-buffered isotonic saline change from biconcave discs to spheres between glass surfaces of a slide and of a coverslip with the echinocyte as an intermediate. A pH increase is a major factor responsible for this disc-sphere transformation or glass effect. It is also observed between surfaces made of various polymers and of mica provided that the distance between them is controlled (0.1 mm). The glass effect is antagonized by serum, plasma, serum albumin, ammonium salts and CO2. It is not observed above a 1-2% hematocrit, but is enhanced by γ-globulins. The sites of reappearance of the spicules are the same and the order of their disappearance is the inverse of the order of their reappearance during the repetitive cycle of the disc-sphere transformation and reversal when a small glass rod is alternatively approached near a site on the erythrocyte surface and withdrawn. A mechanism of erythrocyte shape control has been previously hypothesized in which Band 3 (AE1), the anion exchange protein, plays a central role. Specifically, decrease and increase of the ratio of its outward-facing conformation (Band 3o) and inward-facing conformation (Band 3i) contract and relax the membrane skeleton, promoting the echinocytosis and stomatocytosis, respectively. The Band 3o/Band 3i equilibrium ratio is determined by the Donnan equilibrium ratio of Cl−, HCO3- and H+ (r=Cli-/Clo-=HCO3i-/HCO3o-=Ho+/Hi+), increasing with it. The mechanism could explain by a change of the Donnan ratio the above observations with the assumptions that polymers are permeable to CO2 and that an unstirred layer slows the propagation of the change occurring at the site of approach of the glass rod to peripheral sites. The presence of HCO3- in serum or plasma may be the basis for the absence of the glass effect in these fluids.