Differential gene expression of adenosine A1, A2a, A2b, and A3 receptors in the human enteric nervous system

Adenosine receptors (ADORs) in the enteric nervous system may be of importa nce in the control of motor and secretomotor functions. Gene expression and distribution of neural adenosine Al, A2a, A2b, or A3 receptors (Rs) in the human intestine was investigated using immunochemical, Western blotting, R T-PCR, and short-circuit current (I,,) studies. Adenosine A1R, A2aR, A2bR, or A3R mRNAs were differentially expressed in neural and nonneural layers o f the jejunum, ileum, colon, and cecum and in HT-29, T-84, T98G, and Bon ce ll lines. A1R, A2aR, A2bR, and A3R immunoreactivities (IRs) were differenti ally expressed in PGP 9.5-immunoreactive neurons. A2bR IR occurs exclusivel y in 50% of submucosal vasoactive intestinal peptide (VIP) neurons (interne urons, secretomotor or motor neurons) in jejunum, but not colon; A2aR is al so found in other neurons. A3R IR occurs in 57%, of substance P-positive je junal submucosal neurons (putative intrinsic primary afferent neurons) and less than 10% of VIP neurons. Western blots revealed bands for A3R at 44 kD a, 52 kDa, and 66 kDa. A2aR and A2bR are coexpressed in enteric neurons and epithelial cells. 5'-N-methylcarboxamidoadenosine or carbachol evoked an i ncrease in I-sc. A2bR IR is more prominent than A2aR IR in myenteric neuron s, nerve fibers, or glia. A1R is expressed in jejunal myenteric neurons and colonic submucosal neurons. Regional differences also exist in smooth musc le expression of ADOR IR(s). It is concluded that neural and nonneural Al, A2a, A2b, and A3Rs may participate in the regulation of neural reflexes in the human gut. Clear cell and regional differences exist in ADOR gene expre ssion, distribution, localization, and coexpression. (C) 2001 Wiley-Liss, I nc.