Permeability of dog erythrocytes to lipophilic molecules: solubility and volume effects

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Abstract
Linear diffusion coefficients were determined at 20.degree. C for tritiated water [14C]antipyrine and [14C]alcohols for dog erythrocytes (D), Hb (D2) and plasma (D1). Permeability coefficients (Po) were calculated with the series-parallel pathway model. Analysis of the diffusion coefficients D and D2 indicated that the membrane and Hb provide resistances to diffusion across and through the cell, and that these resistances vary with solute. Po (means .+-. SE) at 20.degree. C were: tritiated water, 554 (.+-. 21) .times. 10-5 cm .cntdot. s-1; methanol, 465 (.+-. 21) .times. 10-5 cm .cntdot. s-1; ethanol, 369 (.+-. 31) .times. 10-5 cm .cntdot. s-1; propanol, 858 (.+-. 89) .times. 10-5 cm .cntdot. s-1; hexanol, 387 (.+-. 20) .times. 10-5 cm .cntdot. s-1 and antipyrine 31 (.+-. 3) .times. 10-5 cm .cntdot. s-1. For the alcohols the Po showed a minimum at ethanol with the values for the lower alcohols close to that for water. The Po of pentanol and hexanol were lower than that of butanol. The alcohols diffused into the erythrocytes about as rapidly as water through lipophilic routes in the plasma membrane. The concept of parallel lipid pathways in the erythrocyte membrane in which molecular size and lipophylicity are factors in determining membrane permeability was supported. In the dog lower permeability to pentanol and hexanol in erythrocytes compared to other isolated cells can be related to the molecular volume of these solutes.