Cell-to-Cell Communication

Grau. teurer Freund. ist aUe Theorie Und griln des Lebens goldner Baum All theory. dear friend. is gray But the golden tree of actual life springs ever green -Goethe Progress achieved in the last 25 years indicates that the establishment of inter cellular junctions at the area of cell contact represents an important mechanism of intercellular communication. Evidence is available that intercellular channels are essential for electrical synchronization in excitable tissues and for the diffusion of molecules from cell to cell. This process of cell-to-cell communication is so reliable that it was pre served throughout the evolutionary scale. As evolution generates diversity it is not surprising that gap junctions are not the same in all systems. It is known, for 2 instance, that junctional permeability is reduced by high free [Ca +]j in some cells or by a fall in pHi in others, or enhanced by cAMP. Our knowledge of the physiological modulators of junctional permeability is still scanty. Moreover, the compartmentalization of the intracellular milieu represents an additional complication in the interpretation of many studies of cell-to-cell communication. The present volume represents an effort to provide the reader with an actualized view of the mechanisms of cell communication and of the physiologi cal and pathological implications of junctional and nonjunctional communica tion. Let us hope that the content of this book helps future studies in establishing a better picture of the cellular and molecular mechanisms involved in the process of intercellular communication.

Inhalt
1 Gap Junction Structure.- 1. Introduction.- 2. Classification of Gap Junctions.- 3. Morphological Characterization of Type I Gap Junctions.- 4. Morphological Characterization of Type II Gap Junctions.- 5. Morphological Characterization of Type III Gap Junctions.- 6. Conclusions.- 7. References.- 2 Modulation of Junctional Permeability.- 1. Introduction: Physiological Considerations.- 2. Are Gap Junctions Really Involved in Cell-to-Cell Communication?.- 3. Junctional Permeability.- 4. Synaptic Transmission and Cell-to-Cell Coupling.- 5. Voltage Dependence.- 6. Antibodies.- 7. Influence of Temperature on gj.- 8. Pathological Implications of Junctional Conductance.- 9. Conclusions.- 10. References.- 3 Permeability and Regulation of Gap Junction Channels in Cells and in Artificial Lipid Bilayers.- 1. Introduction.- 2. Evidence for Cell-to-Cell Channels at Gap Junctions.- 3. Cell-to-Cell Channel Gating and Permeability Modulation.- 4. References.- 4 Electrotonic Coupling in the Nervous System.- 1. Introduction.- 2. Electrotonic Inhibition.- 3. Modulation of Electrotonic Coupling.- 4. Experimental Determination of Electrotonic Coupling.- 5. Conclusion.- 6. References.- 5 Gap Junctions in Smooth Muscle.- 1. Introduction.- 2. Cell-to-Cell Junctions in Smooth Muscle.- 3. Do All Smooth Muscle Cells Have Gap Junctions?.- 4. Regulation of Gap Junctions in Smooth Muscle.- 5. Conclusions.- 6. References.- 6 Cell Communication and Growth.- 1. Introduction.- 2. Basic Principles.- 3. Possible Effects of Gap Junctions on Different Phases of the Cycle.- 4. Evidence for Gap Junction Involvement in Control of Proliferation.- 5. Conclusions and Future Considerations.- 6. References.- 7 Intercellular Communication in Embryos.- 1. Introduction.- 2. The Oocyte.- 3. Early Cleavage Stages.- 4. Early Events in Development.- 5. Compartments, Gradients, and Gap Junctions.- 6. Restriction of Communication Later in Development.- 7. Using Antibodies to Explore the Role of Junctions in Development.- 8. Conclusions.- 9. References.- 8 Mechanisms of Cell-to-Cell Communication Not Involving Gap Junctions.- 1. Chemical Communication between Cells.- 2. On the Release of Neurotransmitters.- 3. Cell-to-Cell Communication through the Extracellular Space.- 4. References.- 9 Cell-to-Cell Communication in Salivary Glands.- 1. Introduction.- 2. Anatomy.- 3. Electrical Evidence.- 4. Diffusional Evidence.- 5. Pharmacology.- 6. Physiological Role of Intercellular Coupling.- 7. Conclusions.- 8. References.- 10 Intercellular Communication in Arthropods: Biophysical, Ultrastructural, and Biochemical Approaches.- 1. Introduction.- 2. Detection and Analysis of Low-Resistance Pathways.- 3. Junctional Permeability to Molecular Tracers.- 4. Ultrastructure of Arthropod Gap Junctions.- 5. Isolation and Biochemical Characterization of Gap Junctions.- 6. Summary and Prospectives.- 7. References.