Passive transmembrane redistributions of phospholipids as a determinant oferythrocyte shape change. Studies on electroporated cells

Echinocytes formed from discocytic erythrocytes by electric field pulses at 0 degrees C return to the discoytic shape upon incubation at 37 degrees C and subsequently turn into stomatocytes. Active and passive components of p hospholipid translocation are involved in this shape recovery. Following lo w-field-strength pulses (5 kV cm(-1)), shape recovery is fully suppressed b y ATPase inhibitors, such as vanadate. When vanadate is only added after st omatocyte formation has been completed, the cells return to the stage of ec hinocytosis prevailing before recovery. At higher field strength (7 kV cm(- 1)) and in particular after repetitive field pulses, the subsequent incubat ion at 37 degrees C results in partial shape recovery even in the presence of vanadate. On the basis of the enhanced passive transmembrane mobilities of phospholipid probes observed previously following electroporation, the s hape changes in the presence of vanadate are proposed to be due to a passiv e net movement of phospholipids from the outer to the inner membrane leafle t, as a consequence of the different mobilities of the various membrane pho spholipids. Repetitive pulses at higher field strengths lead to a progressi vely more discocytic stationary shape during subsequent resealing. This phe nomenon is explained by the progressively increased transbilayer mobility o f the normally almost immobile phospholipid sphingomyelin and a consecutive progressive symmetrization of all membrane phospholipds.