Red blood cell adhesion. II. Interferometric examination of the interaction with hydrocarbon oil and glass.

Using both living and glutaraldehyde-fixed red cells, we have examined adhesion to both oil/saline and glass/saline interfaces by interference reflection microscopy. At low ionic strength, 0.4 mM NaCl, fixed cells adherent to the oil/saline interface show first order whitish yellow zones of closest approach which indicate a separation of similar to or approximately 100 nm. Quantitative interferometry in monochromatic light supports this conclusion. As the salt concentration is increased the separation decreases and the final image shows zero-order black which probably indicates molecular contact with the interface. Similar but less reproducible results were obtained with fixed and unfixed cells on glass. Thes observations show that physical interactions alone can be responsible for adhesion in dilute and concentrated salt solutions. It is not, however, believed that the results necessarily imply the existence of adhesion with a gap in physiological concentrations of salt.