| Unidirectional, proximal-to-distal peristalsis of the renal outflow track is essential for draining urine out of the kidney. Congenital defects that impair this peristaltic process are prevalent, detected in 1 out of 100 births, and are the leading cause of renal failure in children. Despite the high incidence of impaired outflow track function, the mechanisms controlling outflow track development and mature directional contractions remain poorly understood.;The first set of studies described in this thesis elucidate a signaling pathway required for outflow track differentiation. A novel chromagenic substrate that enhances the sensitivity and stability of two-color in situ hybridization, which I have previously developed, is used to show that the signaling molecule, Bone Morphogenic Protein 4 (BMP4), is differentially expressed at the site of outflow track development. Further functional experiments show that outflow track development does not occur in the absence of Bmp signaling, and that Bmp signaling is sufficient for the induction of ectopic outflow track development in cultured embryonic kidneys.;The second set of studies address the mechanisms controlling directional contractions of the mature outflow track. Using a novel adult kidney explant system and newly adapted videomicroscopy and optical mapping techniques, it is shown that electrical and contractile waves of the outflow track muscle initiate at the junction where it joins the connective tissue core of the kidney or the pelvis-kidney junction (PKJ). RT-PCR and immunocytochemical analyses show that hyperpolarization-activated cation (HCN) channels, which are known to be required for initiating electrical activity in the brain and heart, are expressed at the PKJ suggesting that HCN channels may be responsible for triggering myogenic outflow track contractions. Functional studies corroborate this hypothesis as inhibition of HCN channel function cause a loss of electrical activity at the PKJ, randomizing the origin of electric activity in the outflow track, and markedly perturbing contractions. Collectively, these data show that HCN channels play a fundamental role in coordinating outflow track peristalsis, and provide insight into potential causes of common inherited and acquired urinary track disorder. |
