Impaired platelet-derived growth factor receptor expression and function in cultured lower esophageal sphincter circular smooth muscle cells from W/Wv mutant mice

We have previously demonstrated that lower esophageal sphincter (LES) circular smooth muscle (CSM) is functionally impaired in W/W-v mutant mice that lack interstitial cells of Cajal, and speculated that this could be due to altered smooth muscle differentiation. Platelet-derived growth factor (PDGF) is involved in the maturation and differentiation of smooth muscle. To determine whether PDGF expression and (or) function is altered in W/W-v mutant mice, PDGF-R beta expression was measured using RT-PCR, qPCR, and immunocytochemistry, and Ca2+ imaging and perforated patch clamp recordings performed in isolated LES CSM cells. RT-PCR and immunocytochemistry showed significantly reduced PDGF-R beta expression in the LES from mutant as opposed to wild-type mice. Quantitative comparison of CSM cell numbers in histological specimens revealed a significantly increased average cell size in the mutant tissue. The specific PDGF-R beta ligand, PDGF-BB, caused a significant increase in intracellular Ca2+ in cells from the wild-type mice compared with the mutants. Using a ramp protocol, PDGF-BB caused a 2-fold increase in outward K+ currents in cells from the wild-type mice, whereas no significant increase was measured in the cells from the mutants. We conclude that the expression and function of PDGF-R beta in LES CSM from W/W-v mice is impaired, providing further evidence that LES CSM is abnormal in W/W-v mutants.