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D G Warnock

Publications and source records attributed to D G Warnock.

At least 37 records · Page 2Linked to original sources
PubMed1999

Regulation by PKC isoforms of Na(+)/H(+) exchanger in luminal membrane vesicles isolated from cortical tubules.

The present study was designed to determine the Na/H exchanger isoforms present in luminal membrane vesicles (LMV) isolated from rat kidney cortical tubule suspensions, as well as the effects of acute phorbol ester (phorbol myristate acetate, PMA) and angiotensin II (ANG II) pretreatment of suspensions on NHE activity and protein kinase C (PKC) isoform abundance. In LMV, both NHE3 and NHE2 proteins were found by Western blot analysis, but only ethylisopropylamiloride-sensitive and almost completely Hoe-694-resistant Na/H exchange activity was observed from (22)Na uptake and thus attributed to NHE3. PMA pretreatment increased Na/H exchange activity and PKC isoforms alpha, delta, and epsilon abundance in LMV, and these effects were prevented by PKC inhibition. Low-dose ANG II (10(-11) M) pretreatment increased Na/H exchange activity and only PKC-zeta abundance in LMV, and these effects were also prevented by PKC inhibition. After high-dose ANG II (10(-7) M), Na/H exchange activity was decreased in LMV. PKC inhibition did not prevent this effect. In conclusion, the stimulating effects of PMA and low-dose ANG II are explained by the translocation of different isoforms of PKC in LMV, whereas the inhibitory effect of high-dose ANG II is not PKC dependent.

Angiotensin II↗
PubMed1999

Hypertension.

The monogenic forms of human hypertension have yielded to the power of modern genetic techniques in the last several years. With the successful expression cloning of the subunits of the epithelial sodium channel, a whole era has evolved in our basic understanding of the low renin forms of human hypertension. Of note, all of these hypertensive syndromes (Liddle's syndrome, glucocorticoid-remediable aldosteronism, and the apparent mineralocorticoid excess syndrome) share an underlying dysregulation of the activity of the epithelial sodium channel in the cortical collecting tubule. Loss of function defects due to mutations in the channel subunits themselves, or in the mineralocorticoid receptor (pseudohypoaldosteronism, type I) also affect blood pressure regulation consequent to renal salt wasting and dysregulation of the epithelial sodium channel in the cortical collecting tubule.

Biological Transport↗
PubMed1998

Cloning and functional studies of splice variants of the alpha-subunit of the amiloride-sensitive Na+ channel.

The alpha-subunit of the amiloride-sensitive epithelial Na+ channel (alpha ENaC) is critical in forming an ion conductive pore in the membrane. We have identified the wild-type and three splice variants of the human alpha ENaC (h alpha ENaC) from the human lung cell line H441, using RT-PCR. These splice variants contain various structures in the extracellular domain, resulting in premature truncation (h alpha ENaCx), 19-amino acid deletion (h alpha ENaC-19), and 22-amino acid insertion (h alpha ENaC + 22). Wild-type h alpha ENaC and splice variants were functionally characterized in Xenopus oocytes by coexpression with hENaC beta- and gamma-subunits. Unlike wild-type h alpha ENaC, undetectable or substantially reduced amiloride-sensitive currents were observed in oocytes expressing these splice variants. Wild-type h alpha ENaC was the most abundantly expressed h alpha ENaC mRNA species in all tissues in which its expression was detected. These findings indicate that the extracellular domain is important to generate structural and functional diversity of h alpha ENaC and that alternative splicing may play a role in regulating hENaC activity.

Amino Acid Sequence↗
PubMed1998

Immunolocalization of the Na+/H+ exchanger isoform NHE2 in rat kidney.

Four Na+/H+ exchangers (NHE1 to NHE4) have been detected in the kidney. Renal NHE2 expression sites have not been fully established. We have raised rabbit antisera against an oligopeptide related to the amino acids 652 to 661 of rat NHE2. Western blot analysis of plasma membrane fractions isolated from rat renal cortex showed that affinity-purified anti-NHE2 antibody detected an 85-kDa protein in apical but not in basolateral membranes. The labeling of this 85-kDa protein was specifically blocked by preincubation of the antibody with its monomeric peptide, indicating specific recognition. Indirect immunolabeling was performed on sections of paraformaldehyde-fixed rat kidney embedded in paraffin. Strong staining was seen in the apical membrane of cortical thick ascending limbs, distal convoluted tubules, and connecting tubules. Much weaker apical staining was found in medullary thick ascending limbs of Henle. In the inner medulla, some thin limbs were intensively labeled by the anti-NHE2 antibody. No staining could be detected in any segments of the proximal tubule and collecting duct.

Animals↗
PubMed1997

Acute renal failure in the 21st century: recommendations for management and outcomes assessment.

Acute renal failure (ARF) remains a common and potentially devastating disorder affecting as many of 5% of all hospitalized patients, with a higher prevalence in patients in critical care units. ARF is more frequently observed in the setting of multiorgan dysfunction syndrome (MODS) and in elderly patients with complex disease, where mortality is high. Numerous technical advances have not yet impacted favorably on this high mortality rate. This report summarizes recommendations from participants at the National Institutes of Health Conference: "Acute Renal Failure in the 21st Century," May 6 to 8, 1996, in Bethesda, MD. The focus is on categorizing recent clinically relevant developments in the field and on identification of new research initiatives to transfer a new body of knowledge derived from fundamental studies and laboratory investigation to the management of ARF in the new millennium. The development of a multicenter database through cooperative multicenter studies is advocated. Future studies should define the appropriate outcome measures to assess and emphasize the impact of hemodynamic monitoring, adjunctive agents, and adequacy and modality of renal replacement therapy on outcomes in ARF.

Acute Kidney Injury↗
PubMed1997

Relationship of diastolic blood pressure with cyclic GMP excretion among young adults (the CARDIA Study): influence of a family history of hypertension. Coronary Artery Risk Development in Young Adults.

BACKGROUND: Guanosine 3':5'-cyclic monophosphate (cGMP) is the second messenger of nitric oxide and atrial natriuretic factor, and mediates local vasodilatation. These vasodilatory factors are important in blood pressure regulation and possibly in the etiology of hypertension. Urinary cGMP levels among normotensive young adults have not previously been studied. SUBJECTS: A subset of normotensive participants from the CARDIA study (n = 563), aged 23-35 years, was studied. The sample was approximately balanced for sex and race (black/white). METHODS: Twenty-four-hour urinary cGMP levels were measured using an enzyme immunoassay; levels were adjusted for creatinine excretion. The blood pressure, smoking status, and risk factors for hypertension [including a family history of hypertension (FHH), the body mass index, education, alcohol intake, and sodium excretion] were also measured. RESULTS: Women excreted more cGMP than did men, and blacks excreted more cGMP than did whites (both P < 0.0001). Excretion of cGMP was also greater among smokers (P < 0.001) and those with an FHH (P = 0.05), and was related directly and independently to sodium excretion (P < 0.02). The diastolic blood pressure (DBP) was related inversely to the excretion of cGMP among individuals without an FHH (r = -0.36, P < 0.001), but not among individuals with an FHH. In multiple regression analysis, the excretion of cGMP remained related significantly to the DBP and accounted for more variance in DBP than did any other variable among those without an FHH (delta R2 = 0.08, P < 0.001). CONCLUSIONS: Urinary cGMP excretion is related inversely and independently to the DBP among those without an FHH but not among those with an FHH, suggesting that cGMP-related vasodilatation is impaired in those with an FHH. Sex differences in urinary excretion of cGMP are consistent with results from studies showing that estrogen increases the endothelial production of nitric oxide.

Adult↗
PubMed1997

Sodium transporters in health and disease.

Our understanding of sodium transport defects has exploded in the past 18 months, and has provided unique insights into epithelial transport processes and unusual clinical syndromes resulting from mutations of specific transporters. These genetic disorders disturb sodium balance, with both sodium retaining and sodium wasting disorders as the consequence.

Animals↗
PubMed1997

Heterologous expression of rat NHE4: a highly amiloride-resistant Na+/H+ exchanger isoform.

Molecular cloning and expression have previously defined three members of the Na+/H+ exchanger (NHE) gene family NHE1 and NHE2 are sensitive to inhibition by amiloride and its 5'-amino alkyl-substituted analogues, whereas NHE3 is quite resistant to amiloride inhibition. Each of these exchangers has narrowly defined cation specificities for Na+ and Li+. Expression studies with NHE4 have not been as successful, with only a description of modest expression of activity (C. Bookstein, M. W. Musch, A. DePaoli, Y. Xie, M. Villereal, M. C. Rao, and E. B. Chang. J. Biol. Chem. 269: 29704-29709, 1994). We now report that NHE4 activity in stably transfected fibroblasts is activated by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), permitting functional characterization of this NHE isoform. The activating effect of DIDS was unique among the disulfonic stilbenes, and competition studies suggested a cross-linking mechanism. NHE4 is extremely resistant to amiloride and ethylisopropylamiloride inhibition and, unlike other NHE isoforms, affects K+/H+ exchange as well as Na+/H+ and Li+/H+ exchange. These findings demonstrate that NHE4 is a functionally distinct member of the NHE gene family and suggest a unique physiological role for this cation/H+ exchanger.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1997

Evidence for an amiloride-insensitive Na+/H+ exchanger in rat renal cortical tubules.

We have characterized the Na+/H+ exchanger (NHE) isoforms expressed in rat renal cortical tubule fragments. Amiloride sensitivity of the Na(+)-dependent intracellular pH (pHi) recovery in suspended tubules that had been acid loaded by an NH4+ prepulse was determined in nominally CO2/HCO3(-)-free solution, using the fluorescent pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In the presence of 140 mM extracellular Na+, 800 microM amiloride inhibited the rate of Na(+)-dependent pHi recovery by only 65%, demonstrating the presence of a Na(+)-dependent amiloride-insensitive H+ extrusion system. This system was not affected by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid but was activated by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Lowering extracellular Na+ concentration permitted 300 microM amiloride to completely inhibit Na(+)-dependent pHi recovery. These results can be explained by the expression of a Na+/H+ exchange with the pharmacological properties of NHE4. Using reverse transcriptase-polymerase chain reaction, we found specific mRNA for NHE1, NHE2, NHE3, and NHE4 isoforms in the renal cortex. Immunohistochemical studies using polyclonal antibodies against rat NHE4 peptide demonstrated that NHE4 is heterogeneously expressed on basolateral membrane domains of cortical tubules. These results strongly suggest that amiloride-insensitive Na+/H+ exchange expressed in renal cortical tubule suspensions is mediated by NHE4.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1997

Expression of the amiloride-sensitive sodium channel beta subunit gene in human B lymphocytes.

The amiloride-sensitive, epithelial sodium channel (ENaC) is composed of at least three subunits (alpha, beta, and gamma). This study demonstrates that the ENaC beta subunit gene is expressed in human B cell lines, peripheral blood lymphocytes, and lymph node at the mRNA level. Further, this study shows that both wild-type and mutated alleles of the ENaC beta subunit gene are transcribed in human B lymphocytes derived from an individual affected with Liddle's syndrome, an autosomal dominant form of human hypertension.

Alleles↗
PubMed1996

Kidney disease in the first-degree relatives of African-Americans with hypertensive end-stage renal disease.

The incidence of treated end-stage renal disease (ESRD) in the United States is four times more frequent in African-Americans (AAs) than in whites. This is explained neither by a greater prevalence of hypertension and diabetes mellitus nor by socioeconomic issues. To investigate familial risk of renal disease in AAs, we examined the records of 472 AA dialysis patients in Jefferson County, Alabama. Applying strict criteria, we identified 85 index cases of ESRD associated only with hypertension (H-ESRD). We examined the records of 75 index cases and studied the first-degree relatives of 40 patients. The numbers of men and women with H-ESRD were similar (38 and 37, respectively). There was no statistical difference in age at the onset of dialysis (women 53.7 +/- 13.5 years [+/-SD] and men 49.2 +/- 12.2 years; P = 0.0863). We found evidence for renal disease in 26 of 40 (65%) index cases with participating families. Hypertension was present in all 40 families (100%) and diabetes mellitus was present in 24 families (60%). Eighteen of the 75 H-ESRD index patients had a first-degree relative with ESRD. In total, we found evidence for renal disease in 35 of 75 (47%) We conclude that there is a strong concordance of renal disease in the families of AAs with H-ESRD.

Adult↗