The objective of this proposal is to characterize the properties of smooth muscle cells isolated from the mammalian gut. We have developed techniques for isolation of muscle cells from the stomach (guinea pig, dog and man) and gallbladder (dog and man) and have devised an image-splitting micrometric technique for the direct measurement of contraction and relaxation. We have also applied techniques for the indirect measurement of muscle cell response in terms of cellular intermediates: intracellular levels of cyclic nucleotides; 45Ca ions efflux and the phosphorylated fraction of myosin light chain (using IEF/SDS electrophoresis). The specific aims of the proposal are: 1) to identify and characterize smooth muscle receptors for gut peptides; these are known to be present in nerve fibers of the submucous and myenteric plexuses of the gut and are thought to play a physiological role as neurotransmitters or neuromodulators in the control of smooth muscle activity; the most likely candidates are VIP, the opioid peptides (met- and leu-enkephalin), substance P and bombesin. 2) To define the contractile response to peptides by measurement of 45Ca ions efflux and the phosphorylated fraction of myosin light chain, and 3) To define the role of cyclic AMP in smooth muscle relaxation induced by VIP and its homologues and test the possibility that ATP (the putative 'purinergic' relaxant neurotransmitter) and VIP interact synergistically to modulate neurally-induced relaxation.