Stereospecific modulation of the calcium channel in human erythrocytes by cholesterol and its oxidized derivatives.

To study the effect of cholesterol and its pathophysiologically important oxidized derivatives (OSC) on the calcium entry channel, the human red blood cell was used as a model system. The calcium ejecting adenosinetriphosphatase (ATPase) was inhibited by vanadate. The cells were loaded with OSC at concentrations between 1.25 X 10(-5) and 25 X 10(-5) mol/l. 22-Hydroxycholesterol, cholestan-3 beta,5 alpha,6 beta-triol, 5 alpha-cholestan-3 beta-ol,3 beta,5 alpha-dihydroxycholestan-6-one and 3 beta-hydroxy-5 alpha-cholestan-7-one stimulated 45Ca2+ influx by up to almost 90%, whereas 25-hydroxycholesterol, 7 beta-hydroxycholesterol, 20 alpha-hydroxycholesterol and 7-oxocholesterol inhibited influx by up to 75%. Both stimulation and inhibition were dependent on the amount of OSC incorporated into the membrane. More than 90% of the total modification of calcium influx by OSC was accounted for by an influence on the nitrendipine-inhibitable part of influx. Enrichment of cholesterol in the membrane greatly stimulated, and cholesterol depletion inhibited, Ca2+ influx. These results demonstrate that cholesterol and its oxidized derivatives are able to modulate the calcium channel in human red blood cells in a highly stereospecific manner.