Search

During nephrogenesis, renin expression shifts from the vessel walls of interlobular arteries to the terminal portions of afferent arterioles in a wavelike pattern. Since the mechanisms responsible for the developmental deactivation of renin expression are as yet unknown, we hypothesized that the developing renin-angiotensin system (RAS) may downregulate itself via negative feedback to prevent overactivity of renin. To test for a possible role of angiotensin II in the developmental deactivation of renin expression, we studied the development of intrarenal renin expression in mice lacking ANG II [AT.sub.1a], [AT.sub.1b], or [AT.sub.2] receptors and in animals with abolished circulating ANG II due to deletion of the gene for angiotensin I-converting enzyme (ACE). The development of intrarenal renin expression was normal in mice lacking ANG II [AT.sub.1b] or [AT.sub.2] receptors. In animals lacking both ANG II [AT.sub.1a] and [AT.sub.1b] receptors, ACE, or ANG II [AT.sub.1a] receptors, renin expression was normal early and renin disappeared from mature vessels until development of cortical interlobular and afferent arterioles began. The development of cortical vessels in these genotypes was accompanied by a markedly increased number of renin-expressing cells, many of which were ectopically located and attached in a grapelike fashion to the outer vessel perimeter. Although the number of renin-expressing cells declined during final maturation of the kidneys, the atypical distribution pattern of renin cells was maintained. These findings suggest that ANG II does not play a central role in the typical developmental shift in renin expression from the arcuate vessels to the afferent arterioles. During postnatal maturation of mouse kidneys, interruption of the RAS causes severe hyperplasia of renin cells via a mechanism that centrally involves [AT.sub.1a] receptors. However, the distribution pattern of renin cells in adult kidneys with an interrupted RAS does not mimic any normal developmental stage since renin expression is frequently found in cells outside the arteriolar vessel walls in RAS mutants. development; angiotensin II doi: 10.1152/ajprenal.00378.2009.

Although L-type voltage-dependent calcium channels play a major role in mediating vascular smooth muscle cell contraction in the renal vasculature, non-L-type calcium entry mechanisms represent a significant component of vasoactive agonist-induced calcium entry in these cells as well. To investigate the role of these non-voltage- dependent calcium entry pathways in the regulation of renal microvascular reactivity, we have characterized the function of store- and receptor-operated channels (SOCs and ROCs) in renal cortical interlobular arteries (ILAs) of rats. Using fura 2-loaded, microdissected ILAs, we find that the L-type channel antagonist nifedipine blocks less than half the rise in intracellular calcium concentration ([Ca2+]i) elicited by norepinephrine. SOCs were activated in these vessels using the sarco/endoplasmic reticulum [Ca.sup.2+] ATPase (SERCA) inhibitors cyclopiazonic acid and thapsigargin and were dose dependently blocked by the SOC antagonists [Gd.sup.3+] and 2-aminoethoxydiphenyl borate (2-APB) and the combined SOC/ROC antagonist SKF-96365. [Gd.sup.3+] had no effect on the non-L- type [Ca.sup.2+] entry activated by 1 [micro]M NE. A low concentration of SKF-96365 that did not affect thapsigargininduced store-operated [Ca.sup.2+] entry blocked 60-70% of the NE-induced [Ca.sup.2+] entry. Two different calmodulin inhibitors (W-7 and trifluoperazine) also blocked the NE-induced [Ca.sup.2+] entry. These data suggest that in addition to L-type channels, NE primarily activates ROCs rather than SOCs in ILAs and that this receptor-operated [Ca.sup.2+] entry mechanism is regulated by calmodulin. Interestingly, 2-APB completely blocked the NE-induced non-L-type [Ca.sup.2+] entry, implying that SOCs and ROCs in preglomerular resistance vessels share a common molecular structure. receptor-operated channel; store-operated channel; vascular smooth muscle

In the resistance vessels of the renal microcirculation, store- and/or receptor-operated calcium entry contribute to the rise in vascular smooth muscle cell (VSMC) intracellular calcium concentration in response to vasoconstrictor hormones. Short transient receptor potential (TRPC) channels are widely expressed in mammalian tissues and are proposed mediators of voltage-independent cation entry in multiple cell types, including VSMCs. The seven members of the TRPC gene family (TRPC1-7) encode subunit proteins that are thought to form homo- and heterotetrameric channels that are differentially regulated depending on their subunit composition. In the present study, we demonstrate the relative abundance of TRPC mRNA and protein in freshly isolated rat renal resistance vessels, glomeruli, and aorta. TRPC1, 3, 4, 5, and 6 mRNA and protein were detected in both renal resistance vessels and aorta, whereas TRPC2 and TRPC7 mRNA were not expressed. TRPC1, 3, 5, and 6 protein was present in glomeruli. TRPC3 and TRPC6 protein levels were significantly greater in the renal resistance vessels, about six- to eightfold higher than in aorta. These data suggest that TRPC3 and TRPC6 may play a role in mediating voltage-independent calcium entry in renal resistance vessels that is functionally distinct from that in aorta. vascular smooth muscle cells; resistance vessels; aorta; store-operated channel; receptor-operated channel

Norepinephrine directly induces growth of the vascular wall, which may involve not only proliferation of smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) but also augmentation of their migration. To test this hypothesis, growth-arrested SMCs and AFBs from rat aorta were exposed to norepinephrine. Norepinephrine caused dose-dependent migration of both cell types that was dependent on chemotaxis. In contrast, platelet-derived growth factor (PDGF)-BB, used as a positive control, stimulated both chemotaxis and chemokinesis. Only [[alpha].sub.1D]-adrenoceptors (AR) and [[alpha].sub.2]-AR antagonists inhibited norepinephrine migration of SMCs, whereas norepinephrine migration of AFBs was only inhibited by [[alpha].sub.1A]-AR and [[alpha].sub.1B]-AR antagonists; [beta]-AR blockade was without effect. Norepinephrine and PDGF-BB were additive for AFB, but not SMC, migration. Stimulation of migration was reversed at high norepinephrine concentrations (10 [Mu]M); this inhibition was mediated by [[alpha].sub.2]- and [beta]-ARs in AFBs but not in SMCs. Thus norepinephrine induces migration of SMCs and AFBs via different [alpha]-ARs. This action may participate in wall remodeling and norepinephrine potentiation of injury-induced intimal lesion growth. artery; adrenergic receptor; growth; remodeling; platelet-derived growth factor