Differential lateral mobility of IgM and IgG receptors in mouse B lymphocyte membranes.

Anti-Ig induced redistribution of different Ig subclasses was studied as a function of temperature and correlated with membrane phase transitions as revealed by electron spin resonance spectroscopy. Fluorescein isothiocyanate-coupled anti-IgG2 and anti-IgM antibodies induced patching and capping that proceeded with increasing rates from 2 degrees to 40 degrees (measured at 2 degrees intervals). Characteristic temperatures marked the onset of discontinuities in such rate changes. IgG2-bearing lymphocytes displayed discontinuities at 14 degrees , 22 degrees , 28 degrees , and 36 degrees , whereas IgM-bearing lymphocytes displayed discontinuities at 18 degrees , 24 degrees , 32 degrees , and 38 degrees . Electron spin resonance spectroscopy studies using the spin label 2,2-dimethyl-4-butyl-4-penty-N-oxyloxazolidine, a nitroxide-substituted decane, indicated that these temperatures are a function of hydrocarbon phase separations in the B lymphocyte membrane. With a glucosamine-derivative [2-(10-carboxydecyl)-2-hexyl-4,4-dimethyl-3-oxazolidinyloxyl glucosamide] as a probe restricted to the outer monolayer of the plasma membrane, the temperatures 14 degrees and 28 degrees denoted the onset and end, respectively, of a fluidizing process in the outer monolayers of IgG2-bearing lymphocytes. Temperatures of 18 degrees and 32 degrees denoted these boundaries in IgM-bearing lymphocytes. Inner monolayer transitions are associated with the remaining temperatures. We conclude that membranes of IgM-bearing lymphocytes are less fluid than those of IgG2-bearing lymphocytes.