Expression of β-adrenergic receptor subtypes in human normal and dilated ureter
The muscular architecture of the upper urinary tract constitutes a functional but no anatomical syncytium, where the cells are coupled by nexus and crosslinking with low electrical resistance. The action potentials are evoked by spontaneous depolarisation of muscle cells. The sites of peak depolarisation could be termed pace-maker cells. They are localized in the calices. Recent studies have, however, described myofilaments capable of contraction in the proximal tubuli already. Volume and pressure loads on the hollow system have been identified as the regulation mechanism. Modulatory function is directly related to evidence of alpha- and beta-adrenergic receptors, of receptor subtypes, of the adenylate cyclase system, of histamine- and possibly prostaglandin- and serotonin-receptors as well.