Cyclooxygenase inhibitors decrease renal blood flow in settings with decreased effective circulating volume. The present study examined the hypothesis that prostaglandins, prostaglandin E 2 (PGE 2 ) and prostacyclin (PGI 2 ), induce relaxation of human intrarenal arteries through PGE 2 -EP and PGI 2 -IP receptors. Intrarenal arteries were microdissected from human nephrectomy samples (n=53, median diameter ≈362 μm, 88% viable, 76% relaxed in response to acetylcholine). Rings were suspended in myographs to record force development. In vessels with K + -induced tension (EC 70 : –log [mol/L]=1.36±0.03), PGE 2 and PGI 2 induced concentration-dependent relaxation (–log EC 50 : PGE 2 =7.1±0.3 and PGI 2 =7.7). The response to PGE 2 displayed endothelium dependence and desensitization. Relaxation by PGE 2 was mimicked by an EP4 receptor agonist (CAY10598, EC 50 =6.7±0.2). The relaxation after PGI 2 was abolished by an IP receptor antagonist (BR5064, 10 –8 mol/L). Pretreatment of quiescent arteries with PGE 2 for 5 minutes (10 –6 mol/L) led to a significant right shift of the concentration–response to norepinephrine (EC 50 from 6.6±0.1–5.9±0.1). In intrarenal arteries with K + -induced tone, PGE 2 and PGI 2 at 10 –5 mol/L elicited increased tension. This was abolished by thromboxane receptor (TP) antagonist (S18886, 10 –6 mol/L). A TP agonist (U46619, n=6) evoked tension (EC 50 =8.1±0.2) that was inhibited by S18886. Polymerase chain reaction and immunoblotting showed EP4, IP, and TP receptors in intrarenal arteries. In conclusion, PGE 2 and PGI 2 may protect renal perfusion by activating cognate IP and EP4 receptors associated with smooth muscle cells and endothelium in human intrarenal arteries and contribute to increased renal vascular resistance at high pathological concentrations mediated by noncognate TP receptor.

The epithelial sodium channel (ENaC) of the kidney is necessary for extracellular volume homeostasis and normal arterial BP. Activity of ENaC is enhanced by proteolytic cleavage of the g-subunit and putative release of a 43-amino acid inhibitory tract from the g-subunit ectodomain. We hypothesized that proteolytic processing of gENaC occurs in the human kidney under physiologic conditions and that proteinuria contributes to aberrant proteolytic activation. Here, we used monoclonal antibodies (mAbs) with specificity to the human 43-mer inhibitory tract (N and C termini, mAb inhibit , and mAb4C11) and the neoepitope generated after proteolytic cleavage at the prostasin/kallikrein cleavage site (K181-V182 and mAb prostasin ) to examine human nephrectomy specimens. By immunoblotting, kidney cortex homogenate from patients treated with angiotensin II type 1 receptor antagonists (n=6) or angiotensin-converting enzyme inhibitors (n=6) exhibited no significant difference in the amount of full-length or furin-cleaved gENaC or the furin-cleaved-to-full-length ratio of gENaC compared with homogenate from patients on no medication (n=5). Patients treated with diuretics (n=4) displayed higher abundance of full-length and furincleaved gENaC, with no significant change in the furin-cleaved-to-full-length gENaC ratio. In patients with proteinuria (n=6), the inhibitory tract was detected only in full-length gENaC by mAb inhibit . Prostasin/ kallikrein-cleaved gENaC was detected consistently only in tissue from patients with proteinuria and observed in collecting ducts. In conclusion, human kidney gENaC is subject to proteolytic cleavage, yielding fragments compatible with furin cleavage, and proteinuria is associated with cleavage at the putative prostasin/kallikrein site and removal of the inhibitory tract within gENaC.

Hansen PB. Differential effect of T-type voltage-gated Ca 2ϩ channel disruption on renal plasma flow and glomerular filtration rate in vivo.