MEMBRANE E X P A N S I O N OF INTACT E R Y T H R O C Y T E S BY A N E S T H E T I C S

SUMMARY I. Low concentrations of the alcohol and phenothiazine anesthetics protected human erythrocytes from hypotonic hemolysis. 2. The reduction in osmotic fragility amounted to a shift of 0.03 g/Ioo ml NaC1 in the presence of a concentration of anesthetic which reduced osmotic hemolysis b y 50%. 3. The anesthetics protected erythrocytes against hypotonic hemolysis over a iooo-fold range in the rate of hemolysis. The drugs do not act b y changing the rate of hemolysis. 4. Albumin up to 5.6 % did not reduce the amount of the osmotic hemolysis. Albumin did shift the dose-response curve for chlorpromazine to higher concentrations but only slightly reduced the m a x i m u m amount of protection. 5. Low concentrations of the anesthetics did not affect the volumes of the cells in isotonic and moderately hypotonic solutions (down to 0.35 % NaC1). 6 The critical hemolytic relative volume, Ve, was measured b y the GUEST AND WING technique. The Vc obtained b y a Coulter counter and computer method agreed with the Ve obtained using Van Allen hematocrit tubes. The value for Ve in the absence of a n y anesthetics was 1.825 and the membrane area of the prehemolytic sphere was about 136/~2. 7. The anesthetics increased the Vc. At an anesthetic concentration which reduced osmotic hemolysis by 5o %, the Vc increased to 1.925 ; at 95 % reduction in hypotonic hemolysis the Ve went up to around 2.02. The corresponding membrane areas were around 141 and 149 tz z, respectively. At 5 ° % protection, therefore, the membrane area of the intact erythrocyte expanded b y approx. 3 %.