Distinct regional expression of SNARE proteins in the feline oesophagus

Abstract Soluble N-ethylmaleimide-sensitive factors attachment protein receptors (SNAREs), initially found to mediate membrane fusion, have now been shown to also bind and regulate a number of membrane ion channels in neurones and neuroendocrine cells. We recently reported that the SNARE protein SNAP-25 regulates Ca(2+)- activated (K(Ca)) and delays rectifier K(+) channels (K(V)) in oesophageal smooth muscle cells. This raised the possibility that cognate and other SNARE proteins could also be present in the oesophageal smooth muscle cell to regulate these and other functions. Circular muscle tissue sections and single freshly isolated muscle cells from the oesophageal body circular and longitudinal layers, and from lower oesophageal sphincter clasp and sling regions were studied. The subcellular location of SNAP-23, SNAP-25, syntaxins 1 to 4, and vesicle-associated membrane protein (VAMP)-2 were explored using a laser scanning confocal imaging system. Feline oesophageal smooth muscle of all regions examined demonstrated the presence of SNAP-23, SNAP-25, syntaxins 1 to 4, and VAMP-2 on the plasma membrane. The intensity of these syntaxins and SNAP-25/-23 proteins varied between the different muscle groups of the oesophagus. In some regions, some SNARE proteins were also noted in the muscle cell cytoplasm. No differential expression was found for VAMP-2. The differential expression of SNAP-25 and its regulation of K(+) channels indicate the important role of SNAP-25 in regulating the distinct membrane excitability and contractility along the smooth muscle of the oesophagus. This is further contributed by its interactions with the cognate syntaxins, which are also differentially expressed in the muscle groups of the oesophageal body and lower oesophageal sphincter (LOS). These SNARE proteins probably have other functions in the smooth muscle cell, such as regulating vesicular transport processes.