Chemical signaling from colonic smooth muscle cells to DRG neurons in culture

Transduction mechanisms between target cells within the intestinal wall and peripheral terminals of extrinsic primary afferent neurons are poorly unde rstood. The purpose of this study was to characterize the interactions betw een smooth muscle cells from the rat distal colon and lumbar dorsal root ga nglion (DRG) neurons in coculture. DRG neurons visually appeared to make co ntact with several myocytes. We show that brief mechanical stimulation of t hese myocytes resulted in intracellular Ca2+ concentration ([Ca2+](i)) tran sients that propagated into 57% of the contacting neurites. Direct mechanic al stimulation of DRG neurites cultured without smooth muscle had no effect . We also show that colonic smooth muscle cells express multiple connexin m RNAs and that these connexins formed functional gap junctions, as evidenced by the intercellular transfer of Lucifer yellow. Furthermore, thapsigargin pretreatment and neuronal heparin injection abolished the increase in neur ite [Ca2+](i), indicating that the neuronal Ca2+ signal was triggered by in ositol 1,4,5-trisphosphate-mediated Ca2+ release from intracellular stores. Our results provide evidence for intercellular chemical communication betw een DRG neurites and intestinal smooth muscle cells that mediates the excha nge of second messenger molecules between different cell types.