[Gap junctions in the human urinary bladder]

Gap junctions are intercellular contacts important for the synchronization of muscle cell activity through electrical coupling. Since the role of gap junctions for the function of smooth bladder muscle is still a matter of debate, we investigated the occurrence of gap junctions and the gap junctional protein connexin (Cx) 45 in the detrusor of the nonobstructed stable human bladder.Detrusor biopsies from 6 patients aged 64 (55-72) years with stable nonobstructed bladders were investigated for the occurrence of gap junctions by electron microscopy, molecular biological techniques and immunohistochemistry.Transmission electron microscopy and freeze fracture showed the presence of gap junction at plasma membranes of detrusor smooth muscle cells. By reverse transcriptase (RT) polymerase chain reaction (PCR) and in situ hybridization, we found an expression of Cx45 in the detrusor. These data were confirmed by immunolocalization of Cx45 on smooth muscle cells.This study provides morphological as well as molecular biological and immunohistochemical evidence that bladder smooth muscle cells are electrically coupled.