P2X7 subunit-like immunoreactivity in the nucleus of visceral smooth muscle cells of the guinea pig

P2X receptors are adenosine 5′-triphosphate (ATP)-gated cation-selective channels. Seven cloned subunits (P2X1–7) are found in the plasma membrane of many cells in the brain and periphery. ATP-dependent opening of nuclear membrane channels, which resemble P2X7 receptors, has been reported previously. Therefore, the aim of this study was to use specific antisera to examine P2X7 receptor subunit expression in the nucleus of cells in visceral organs. In sections of the guinea pig vas deferens and bladder, widespread nuclear immunoreactivity was observed in smooth muscle, epithelial, and lamina propria cells using two antisera raised against different sequences within the P2X7 subunit. Nuclear immunostaining was also seen in a variety of cell types in the myocardium, lung, stomach, ileum, and colon of the guinea pig. In all tissues, omission of the primary antisera or preincubation of the primary antisera with the antigenic peptide resulted in the loss of specific immunostaining, as did dilution of the antisera beyond 1:32000 or omitting antigen retrieval. Western blot analysis revealed that the anti-P2X7 antiserum recognised a protein in membrane preparations from both guinea pig vas deferens nuclei and HEK-293 cells transfected with P2X7 subunits. Thus, the nuclear expression of P2X7 receptors appears to be widespread in smooth muscle and epithelial cells of visceral organs.