Bidirectional regulation of renal cortical Na+,K+-ATPase by protein kinase C.

We examined the role of protein kinase C (PKC) in the regulation of Na+,K+- ATPase activity in the renal cortex. Male Wistar rats were anaesthetized and the investigated reagents were infused into the abdominal aorta proximally to the renal arteries. A PKC-activating phorbol ester, phorbol 12,13-dibutyrate (PDBu), had a dose-dependent effect on cortical Na+,K+-ATPase activity. Low dose of PDBu (10(-11) mol/kg per min) increased cortical Na+,K+-ATPase activity by 34.2%, whereas high doses (10(-9) and 10(-8) mol/kg per min) reduced this activity by 22.7% and 35.0%, respectively. PDBu administration caused changes in Na+,K+-ATPase Vmax without affecting K(0.5) for Na+, K+ and ATP as well as Ki for ouabain. The effects of PDBu were abolished by PKC inhibitors, staurosporine, GF109203X, and Gö 6976. The inhibitory effect of PDBu was reversed by pretreatment with inhibitors of cytochrome P450-dependent arachidonate metabolism, ethoxyresorufin and 17-octadecynoic acid, inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and LY294002, and by actin depolymerizing agents, cytochalasin D and latrunculin B. These results suggest that PKC may either stimulate or inhibit renal cortical Na+,K+-ATPase. The inhibitory effect is mediated by cytochrome P450-dependent arachidonate metabolites and PI3K, and is caused by redistribution of the sodium pump from the plasma membrane to the inactive intracellular pool.

Is Survival Possible Without Arachidonate Metabolites in the Brain During Systemic Infection?

The central nervous system mediates a coordinated set of biological responses during systemic immune stimuli. These responses are essential for the organism to eliminate invading pathogens and restore health. Coincidentally, centrally produced prostaglandins play a determinant role in activating the neuronal circuits involved in the control of autonomic functions.

Role of cytochrome P-450 arachidonate metabolites in endothelin signaling in rat proximal tubule

We examined the rat proximal tubule (PT) response to endothelin-1 (ET-1) in terms of 20-hydroxyeicosatetraenoic acid (HETE) dependency. Arachidonic acid (AA) (1 μM) decreased ouabain-sensitive 86Rb uptake from 2.1 ± 0.1 to 0.3 ± 0.08 ng Rb · 10 μg protein−1 · 2 min−1( P < 0.05); 20-HETE (1 μM) had similar effects. Dibromododecenoic acid (DBDD) (2 μM), an inhibitor of ω-hydroxylase, abolished the inhibitory action of AA on86Rb uptake whereas the PT response to 20-HETE was unaffected. ET-1 at 0.1, 1, 10, and 100 nM reduced 86Rb uptake from 2.8 ± 0.3 in control PTs to 2.4 ± 0.2, 1.7 ± 0.1, 0.67 ± 0.08, and 0.1 ± 0.03 ng Rb · 10 μg protein−1 · 2 min−1, respectively. DBDD (2 μM) abolished the inhibitory effect of ET-1 on86Rb uptake as did BMS182874 (1 μM), an ETA-selective receptor antagonist. ET-1 (100 nM) significantly increased PT 20-HETE release by ∼50%, an effect prevented by DBDD. N ω-nitro-l-arginine-methyl ester (l-NAME), given for 4 days to inhibit nitric oxide synthase (NOS), increased arterial pressure from 92 ± 12 to 140 ± 8 mmHg and increased endogenous release of 20-HETE from isolated PTs (measured by gas chromatography/mass spectrometry). Inl-NAME-treated PTs, but not in control PTs, 0.1 μM AA inhibited ouabain-sensitive 86Rb uptake by >40%; the response to AA was attenuated by DBDD. We conclude that, in the PTs, 1) 20-HETE is a second messenger for ET-1 and 2) conversion of AA to 20-HETE is augmented when NOS is inhibited.