Smooth muscle is responsible for the contractility of hollow organs, such as blood vessels, the gastrointestinal tract, the bladder, and the uterus. The human esophagus contains three layers of muscle in its walls, the outer longitudinal and inner circular layers of the main muscular coat and the muscular layer of the mucosa. Visceral smooth muscle cells make up all three layers along the entire organ except for the most rostral few centimeters. Smooth muscle contraction is critical to peristalsis in the human esophagus and the contraction may be mediated by activation of phospholipase through increased intracellular Ca2+, G protein activation, and activation of PKCepsilon-dependent mechanisms. Other in vitro studies have shown that cultured human esophageal smooth muscle cells (HEsSMC) express voltage-dependent Na(+) channels. HEsSMC from ScienCell Research Laboratories are isolated from the human esophagus. HEsSMC are cryopreserved at passage one and delivered frozen. Each vial contains >5 x 105 cells in 1 ml volume. HEsSMC are characterized by immunofluorescence with antibodies specific to α-smooth muscle actin. HEsSMC are negative for HIV-1, HBV, HCV, mycoplasma, bacteria, yeast and fungi. HEsSMC are guaranteed to further expand for 15 population doublings under the conditions provided by ScienCell Research Laboratories Recommended Medium It is recommended to use Smooth Muscle Cell Medium (SMCM, Cat. #1101) for culturing HEsSMC in vitro.