Renal sodium metabolism, a major determinant of blood pressure, is regulated with great precision by a variety of endocrine, autocrine, and neuronal factors. Although these factors are known to regulate sodium metabolism by affecting the rate of tubular sodium reabsorption, the molecular mechanisms by which they act are poorly understood. Na+,K(+)-ATPase plays a pivotal role for sodium reabsorption in all tubular segments. The activity of this enzyme can be dynamically regulated by phosphorylation and dephosphorylation. Here we summarize both old and new evidence that several major substances believed to be involved in the regulation of sodium metabolism and blood pressure, i.e., the antidiuretic agents angiotensin II and norepinephrine, and the diuretic agents dopamine and atrial natriuretic peptide (ANP), may achieve their effects through a common pathway that involves reversible activation/deactivation of renal tubular Na+,K(+)-ATPase. Regulation of Na+,K(+)-ATPase activity was studied using a preparation of single proximal tubule (PT) segments, dissected from rat kidneys. Na+,K(+)-ATPase activity was stimulated by angiotensin II and the alpha-adrenergic agonist, oxymetazoline, at physiological, nonsaturating Na+ concentrations. These stimulatory effects were blocked by dopamine and ANP as well as by their respective second messengers, cAMP and cGMP. They were also blocked by the specific protein phosphatase 2B inhibitor FK506. These results indicate that regulation of sodium excretion by norepinephrine, angiotensin II, dopamine, and ANP can be accounted for by a bidirectionally regulated intracellular protein phosphorylation cascade that modulates the activity of renal tubular Na+,K(+)-ATPase.

In our opinion, a 60 day follow-up is sufficient to catch the majority of deaths in ARF patients treated with CRRT. The patients in the RIFLE-F category had a significantly higher mortality than RIFLE-R and -I patients.

The molecular mechanisms underlying the regulation of sodium excretion are incompletely known. Here we propose a general model for a bi-directional control of tubular sodium transporters by natriuretic and antinatriuretic factors. The model is based on experimental data from studies on the regulation of the activity of Na+,K+-ATPase, the enzyme that provides the electrochemical gradient necessary for tubular reabsorption of electrolytes and solutes in all tubular segments. Regulation is carried out to a large extent by autocrine and paracrine factors. Of particular interest are the two catecholamines, dopamine and norepinephrine. Dopamine is produced in proximal tubular cells and inhibits Na+,K+-ATPase activity in several tubule segments. Renal dopamine availability is regulated by the degrading enzyme, catechol-O-methyl transferase. Renal sympathetic nerve endings contain norepinephrine and neuropeptide Y (NPY). Activation of alpha-adrenergic receptors increase and activation of beta-adrenergic receptors decrease Na+,K+-ATPase activity. alpha-Adrenergic stimulation increases the Na+ affinity of the enzyme and thereby the driving force for transcellular Na+ transport. NPY acts as a master hormone by synergizing the alpha- and antagonizing the beta-adrenergic effects. Dopamine and norepinephrine control Na+,K+-ATPase activity by exerting opposing forces on a common intracellular signaling system of second messengers, protein kinases and protein phosphatases, ultimately determining the phosphorylation state of Na+,K+-ATPase and thereby its activity. Important crossroads in this network are localized and functionally defined. Phosphorylation sites for protein kinase A and C have been identified and their functional significance has been verified.

The cellular localization of DARPP-32, a dopamine-and cAMP-regulated phosphoprotein of Mr 32,000 that appears to mediate certain actions of dopamine in the mammalian brain by acting as an inhibitor of protein phosphatase 1, was studied in the kidney of several species. DARPP-32 mRNA and DARPP-32-like inmunoreactivity were found in the cytoplasm of cells in the thick ascending limb of the loop of Henle. The specific dopamine DA, agonist SKF 82526 caused a dose-dependent inhibition ofNa+,K+-ATPase activity, which could be blocked by SCH 23390, a specific DA, antagonist, and by PKI-(5-24) amide, a specific inhibitor of cAMP-dependent protein kinase. The results indicate that DA1 dopamine receptors and DARPP-32, an intracellular third messenger for dopamine, are part of the signal-transduction process for dopamine acting on renal tubule cells.The neurotransmitter dopamine may play an important role in control of renal function. Dopamine is synthesized within the kidney (1) and acts locally to produce natriuresis (2-5) and vasodilation (6). Although these roles for dopamine in kidney physiology are well established, the cellular localization of renal dopamine receptors has not been defined.DARPP-32, a dopamine-and cAMP-regulated phosphoprotein with an apparent molecular weight of 32,000 by SDS/PAGE, has been purified from cytosol of bovine caudate nucleus (7,8). The complete amino acid sequence of bovine brain DARPP-32 has been determined (9), and its cDNA has been isolated and sequenced (10). In the central nervous system, DARPP-32 has been shown to be localized to dopaminoceptive cells containing the D1 dopamine receptor (11,12). It appears to serve as an intracellular third messenger mediating the actions of dopamine at these receptors (7,8,(11)(12)(13). Thus, the phosphorylation of DARPP-32 in intact nerve cells is increased by dopamine acting on D1 receptors, stimulation of adenylate cyclase, formation of cAMP, and stimulation of cAMP-dependent protein kinase (7,8). DARPP-32, in its phosphorylated form, is a potent inhibitor of phosphoprotein phosphatase 1 (14) and has amino acid sequence homology with phosphatase inhibitor 1 (I-1), also an inhibitor of phosphatase 1 (9).DARPP-32 has been analyzed primarily in the central nervous system. However, DARPP-32-like immunoreactivity has been detected in brown fat cells in pig (15), and the protein has been identified and purified from bovine adipose tissue (16). Previous studies have also identified DARPP-32 in ciliary epithelium (17) and in adrenal chromaffin cells, parathyroid cells, and choroid plexus (13). Evidence has been obtained for the presence of D1-like receptors in several of these tissues (18)(19)(20)(21)(22). Thus, DARPP-32 appears to be a useful marker for cells containing the central (D1) and peripheral (DA1) dopamine receptors. In the present study we investigated the cellular localization of DARPP-32 and, for purposes of comparison, I-1, in the kidney. Both proteins were localized in the same cells of a specific portion of the loop of Henle; ...

Dopamine inhibits Na',K+-ATPase activity in several renal tubule segments and thereby regulates urinary Na" excretion. We now show that a phosphopeptide of 31 amino acids, corresponding to residues 8-38 of the protein phosphatase inhibitor DARPP-32 (dopamine-and cAMPregulated phosphoprotein ofMr 32,000), mimics the inhibitory action of dopamine on Na',K+-ATPase activity in renal tubule cells from the ascending limb of the loop of Henle. The dephosphorylated form of the peptide Is ineffective. The results indicate that dopamine acts through a protein phosphorylation pathway to regulate the activity of an ion pump. In addition, the data suggest that inhibition of protein phosphatase 1 by phophorylated DARPl-32 is a component of the mechanism by which dopatine regulates urinary Na`excretion. Na+,K+-ATPase regulates a number of vital functions, including intracellular electrolyte homeostasis and pH, cell volume, membrane potential, cellular uptake of amino acids, and transcellular Na' transport (1). Na',K+-ATPase is particularly abundant in kidney and brain. Dopamine has been shown to inhibit the activity of this enzyme in neostriatal neurons (2) and in several segments of the rat renal nephron, including the proximal tubule (3, 4), the thick ascending limb (TAL) of the loop of Henle (5), and the cortical collecting tubule (6). The peripheral actions of dopamine are critical for the regulation of Na+ and extracellular volume homeostasis and for the regulation ofblood pressure (7). In fact, dopamine is the drug of choice in many clinical situations in which renal function is compromised. Therefore, an understanding of the cellular and molecular mechanisms by which dopamine regulates cellular Na' homeostasis is of interest both to cell biology and to clinical medicine.DARPP-32 (dopamine-and cAMP-regulated phosphoprotein of Mr 32,000) is localized to cells containing the D1 subclass of dopamine receptor, including medium-sized spiny neurons of the neostriatum (8-10) and renal tubule cells of the TAL (5). (In this report we have used the terminology D1 and D2 to classify dopamine receptors. In the kidney, the functional equivalents of the D1 and D2 dopamine receptors are often referred to as the DA1 and DA2 receptors, respectively.) Phosphorylation ofDARPP-32 on threonine-34 converts it into a potent inhibitor (K-10-9M) (11) of protein phosphatase 1, a major protein phosphatase in virtually all tissues (12). Although the biochemical mechanism of action of DARPP-32 has been established (11), its precise physiological role in signal transduction is not yet understood. Distinct neurotransmitter pathways regulate the phosphorylation (13) and dephosphorylation (14) of DARPP-32. However, there has been no direct evidence that DARPP-32 mediates any of the actions of dopamine or other neurotransmitters that regulate its state of phosphorylation. In this study, we present evidence that phosphorylated DARPP-32 mimics D1 dopamine receptor agonists in inhibiting Na',K+-ATPase activity in renal tubule segments from the medul...

PKC plays a central role for the regulation of renal function. PKC consists of a family of isoenzymes. By employing Northern blot techniques we have demonstrated that mRNA transcripts for the classical Ca(2+)-dependent, diacylglycerol-activated isoform alpha, the novel, Ca(2+)-independent isoform delta and the atypical isoform zeta are abundantly expressed in the rat kidney. The novel PKC-epsilon was weakly expressed. The classical PKCs beta I, beta II and gamma could not be detected. The mRNA expression of PKC-delta and -zeta increased with age. The intrarenal localization of PKC-alpha, -delta and -zeta isoforms were studied in the adult kidney using in situ hybridization. In the cortex, the PKC-alpha isoform showed the strongest hybridization signal. PKC alpha, delta and zeta were all distributed in the outer medulla. The PKC-alpha probe detected particularly strong signal in the outer stripe of the outer medulla. Western blot confirmed the presence of the PKC-alpha, -delta and -zeta enzymes in renal tissue. The results show cell-specific and developmentally-dependent expression of three types of PKC isoforms with different responses to diacylglycerol and calcium. The developmental increase of both PKC-delta and PKC-zeta suggests a specific role for these isoforms for the functional regulation of the mature kidney.

PurposeTo identify the prevalence and preventability of adverse drug reactions (ADRs) in an emergency ward setting in a tertiary hospital in Sweden and to what extent the detected ADRs were reported to the Medical Product Agency (MPA).MethodsIn this prospective cross sectional observational study, 706 patients admitted to one of the Emergency Wards, at the Karolinska University Hospital in Solna, Stockholm during September 2008 –September 2009, were included. The electronic patient records were reviewed for patients’ demographic parameters, prevalence of possible ADRs and assessment of their preventability. In addition, the extent of formal and required ADR reporting to national registers was studied.ResultsApproximately 40 percent of the patient population had at least one possible ADR (n = 284). In the multivariable regression model, age and number of drugs were significantly associated with risk of presenting with an ADR (p<0.01 and p<0.001, respectively). Sex was not identified as a significant predictor of ADRs (p = 0.27). The most common ADRs were cardiovascular, followed by electrolyte disturbances, and hemorrhage. In 18 percent of the patient population ADRs were the reason for admission or had contributed to admission and 24% of these ADRs were assessed as preventable. The under-reporting of ADRs to the MPA was 99%.ConclusionsADRs are common in Emergency Medicine in tertiary care in Sweden, but under-reporting of ADRs is substantial. The most frequent ADRs are caused by cardiovascular drugs, and significantly associated with age and number of drugs. However, only a minority of the detected serious ADRs contributing to admission could have been avoided by increased risk awareness.

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