General Aspects of Intracellular Measurements of Ions

Abstract

The intracellular space is an extremely complex sample (Fig. 8.1) [Alberts et al. 83]. An idea of the complexity of a typical eucaryotic cell, the liver hepatocyte, is given below:

• the cytosol accounts for only about half (54%) of the total volume of a cell

• mitochondria (22%), rough (9%) and smooth endoplasmic reticulum cisternae including Golgi cisternae (6%), nucleus (6%), peroxisomes (1%) and lysosomes (1%) are important organelles

• a single cell contains about 1700 mitochondria, 300–400 peroxisomes and lysosomes, and 10⁷ ribosomes

• most of the total membrane area is not made up of the plasma membrane itself (2%), but is made up of the internal membranes (e.g. rough endoplasmic reticulum membrane (35%), smooth endoplasmic reticulum membrane (16%), mitochondrial outer (7%) and inner (32%) membrane)

• a single cell contains about 20% proteins, corresponding to about 10¹⁰ protein molecules of approximately 10⁴ different types

• the cytosol consists of a dense network of protein filaments, the cytoskeleton.