In organizing the present volume, we had two intentions. The first was to present the best current understanding of the mechanisms of calcium mobilization during excitation contraction coupling of smooth muscle at a level suited to the needs of professionals interested in smooth muscle pharmacology and pathophysiology, while remaining appreciable by graduate and medical students. The second intention was to provide in sight into present-day controversies, as well as the latest ad vances achieved by researchers in this field. Thus, we have thor oughly discussed both the techniques and the concepts derived from their application. An attempt has also been made here to answer a number of profoundly important questions: What are the mechanisms and agents responsible for the control of contractility? What are the accompanying changes in the state of intracellular calcium ions and the mechanisms responsible for them? How does the regula tion of contractility occur directly at the level of the actomyosin activity? What role do gap junctions play in cell-to-cell coupling? What are the roles of cholinergic, adrenergic, peptidergic, and nonadrenergic noncholinergic interactions in calcium mobiliza tion in smooth muscle? What changes occur in hypertension? The impact of these recent techniques on future research is also reflected upon."

The differentiation between the muscarinic and the nicotinic ef- fects of acetylcholine led to the subdivision of the cholinergic ner- vous system into two categories. Further studies showed that stimu- lating and inhibiting muscarinic effects could be demonstrated in different organs. For instance, gastric secretion and gastrointestinal motility are stimulated, while heart rate and the vascular muscula- ture are inhibited. For decades, it could not be determined whether the various ef- fects were mediated by different subgroups of muscarinic receptors, but eventually, with the availability of agonists and antagonists to muscarinic receptors, and using various techniques, the existence of at least two such subgroups could be ascertained . . Mt receptors are defined by their high affinity for the antagonist pirenzipine in comparison to M2 receptors. This subdivision of muscarinic receptors has since been proved beyond doubt by experi- ments in vivo and in vitro, by receptor binding studies, by histoauto- radiography, and by electrophysiological studies. However, these different classes of muscarinic receptors have not been found to relate to different types of effects; instead both excit- atory and inhibitory effects appear to be linked to each class. For ex- ample, excitation of gut motility and inhibition of cardiac contrac- tile activities both appear to be mediated by M2 receptors, while ex- citation of some nerves in sympathetic ganglia and inhibition of some myenteric nerves may be mediated by M receptors.

In organizing the present volume, we had two intentions. The first was to present the best current understanding of the mechanisms of calcium mobilization during excitation contraction coupling of smooth muscle at a level suited to the needs of professionals interested in smooth muscle pharmacology and pathophysiology, while remaining appreciable by graduate and medical students. The second intention was to provide in sight into present-day controversies, as well as the latest ad vances achieved by researchers in this field. Thus, we have thor oughly discussed both the techniques and the concepts derived from their application. An attempt has also been made here to answer a number of profoundly important questions: What are the mechanisms and agents responsible for the control of contractility? What are the accompanying changes in the state of intracellular calcium ions and the mechanisms responsible for them? How does the regula tion of contractility occur directly at the level of the actomyosin activity? What role do gap junctions play in cell-to-cell coupling? What are the roles of cholinergic, adrenergic, peptidergic, and nonadrenergic noncholinergic interactions in calcium mobiliza tion in smooth muscle? What changes occur in hypertension? The impact of these recent techniques on future research is also reflected upon."