Translational diffusion in the plasma membrane of single cells as studied by fluorescence microphotolysis

The imagination has been fired by the idea that biological mem- branes might be Z-dimensional fluid. Provided, for instance, that membrane viscosity was not much larger than that of the cytoplasm, the reduction of dimensionality would shorten diffusion times and thus enhance reaction rates in membranes over those in the cytoplasm (Adam and Delbrück, 1968). Translational diffusion in membranes could be crucial for the propagation of information in the plane of the membrane, a case which might apply for fertilization and differentiation, and across the membrane as in hormonal regulation (Cuatrecasas, 1974). Furthermore, diffusion in membranes potentially could channel energy, metabolites and electrons through the cell body possibly involving carrier proteins specialized in lateral membrane transport (Skulachev, 1980)