Gastric emptying is regulated by pressures and resistances across the gastroduodenal junction (GDJ). These factors are produced by the muscular activities of the stomach, pyloric sphincter and proximal small intestine. Motor activities in these regions are determined by intrinsic rhythmic electrical activity that is modulated by hormones and inputs from enteric motor neurons. We will investigate the mechanisms of intrinsic pacemaker activity and the role of interstitial cells of Cajal (ICC) as pacemaker cells. We will also determine the role of ICC in mediating neural inputs to the GDJ. The first part of the study will investigate the hypothesis that certain classes of ICC produce pacemaker activity in the antrum, pylorus and duodenum. Use of c-Kit mutant mice and specific reagents to block the development of ICC will help determine the role of ICC in pacemaking in each region. We will use similar preparations to determine the role of ICC in propagation of slow waves. Isolated and cultured ICC will be used to study the basic ionic mechanisms and pharmacology of pacemaker activity in the stomach and duodenum. We will also study how the frequency of slow waves is regulated in the terminal antrum and what ionic conductances may participate in setting frequency. We hope to determine the specific mechanisms that cause to the abnormal frequencies and arhythmias observed in numerous clinical conditions that are associated with gastric empyting disorders in human patients. Recent studies have also demonstrated an important role for ICC in mediating neural inputs. Experiments proposed will clarify the anatomical relationships between ICC and intrinsic motor neurons and determine the degree of innervation of ICC vs. smooth muscle cells. By removing ICC and testing the effects of these manipulations on neurotransmission, we will also obtain novel information about the importance of ICC in regulating neural inputs to the GDJ. We also intend to find out which ionic conductances are expressed by ICC that allow them to respond in a specialized manner to enteric neurotransmitters. It is also possible that ICC modulate neurotransmssion by release of nitric oxide or by protection of nitric oxide released from neurons. Studies are designed to test the importance of these features. Information from these studies will greatly expand our basic knowledge of the mechansims that regulate gastric emptying. This information will be useful in designing rational therapies for patients that suffer from problems resulting from inappropriate gastric emptying.