Junctional communication between animal cells

1. The literature concerning the structure, permeability and function of gap junctions has been reviewed. 2. Aspects of the occurrence, metabolism and biological activities of the family of compounds derived from vitamin A known as retinoids, have been described. 3. A method has been developed by the modification of established procedures for the purification of gap junctions from small numbers of cultured cells (10 cells). 4. The method produces fractions which appear by electron microscopy to be rich in gap junctions. SDS PAGE of these fractions shows only one major protein component which has an apparent of 16,000 (16K). The yield of the 16K component in different isolations has been examined, and is sufficiently reproducible (+/- 5%) to allow the method to be used for estimating junctional area by measuring junctional protein. 5. Further evidence has been obtained for the junctional origin of the 16K protein : a) it is the major (sometimes only detectable) component in junctional preparations from a wide variety (mammalian, amphibian, piscine) of cultured cell types. b) the recovery of the 16K component from Chinese hamster fibroblasts (V79 cells) before, during and after treatment with the tumour promoter, phorbol 12 myristate 13 acetate (TPA) parallels the changes in junctional area measured morphometrically by Yancey et al, (1982) in freeze-fractured samples. It has been shown that trans retinoic acid (10 muM) inhibits junctional communication (assayed by measuring [3H]-uridine nucleotide transfer between cells in culture) between a variety of cell types. 7. An estimate has been made of the rate of inhibition of junctional communication after the addition of retinoic acid to cell cultures. It has been shown to be rapid (half life of the open state = a few minutes or less) and to be fully and rapidly reversible. 8. Evidence has been obtained which indicates that the inhibition of junctional communication between rat liver (BRL) epithelial cells and between Syrian hamster fibroblasts (Cl 3 cells) by 10-4 M trans retinoic acid appears to be caused by a reduction of junctional permeability and not by loss of the gap junction structures. 9. It has been shown that 10-5 trans retinoic acid does not affect junctional communication between BRL cells and between Cl 3 cells but that intermediate concentrations 8*10