It is not a particularly rewarding task to engage in writing a book on a
subject which is undergoing a rapid and potentially revolutionary
develop- ment, but, on the other hand, the investigation of transport of
substances into and out of cells has reached a stage of maturity or at
least of self- realization and this fact alone warrants a closer
examination of the subject. No one will doubt at present that the
movement-mostly by selective translocation-of substances, ranging from
hydrogen ions to deoxyribo- nucleic acids, across the cell-surrounding
barriers represents one of the salient features of a living cell and
that, if we are permitted to go so far, the cessation of the selective
transport processes might be considered as the equivalent of cell death.
Hardly anybody will question the premise that cell and tissue
differentiation within the ontogenetic development of an organism is
closely associated with properties of the outer cell face. Perhaps no
serious scholar will attempt to refute the concept that mem- branes with
characteristic morphology and composition represent the ar- chitectural
framework for the whole cell. And probably no experienced biologist will
raise objections to the belief that many physiological processes, like
nervous impulse conduction and other electrical phenomena of cells and
tissues or their volume changes, are associated with membrane-regulated
shifts of ions and molecules.
