bluuebunny/crossref_metadata_2025 huggingface dataset:
Basolateral membrane H-OH-HCO3 transport in the proximal tubule
Authors: Preisig P. A. , Alpern R. J.
Published: December 2017

This review focuses on the basolateral membrane mechanisms of H-OH-HCO3 transport in the proximal tubule. The mechanism that has the greatest transport capacity and mediates most of transepithelial H-HCO3 transport is the electrogenic, Na-3HCO3 cotransporter. This transporter has been extensively characterized in the salamander, rat, and rabbit proximal tubule, and has now been found in a number of other epithelia that effect transepithelial NaHCO3 transport. Transporter rate is sensitive to intra- and extracellular [Na], intra- and extracellular [HCO3]/pH, and cell voltage. Adaptations in transporter activity have been demonstrated in chronic metabolic acidosis and alkalosis, chronic respiratory acidosis and alkalosis, and chronic hyperfiltration. In addition to the Na-3HCO3 cotransporter, the basolateral membrane possesses both Na-dependent and -independent Cl-HCO3 exchangers, a H leak, and in the S3 proximal tubule an Na-H antiporter. The role of these H-OH-HCO3 transport mechanisms in transcellular HCO3 and Cl absorption and pHi defense is discussed.
Characterization of apical and basolateral membrane conductances of rat inner medullary collecting duct
Authors: Stanton B. A.
Published: December 2017

Initial segments of the inner medullary collecting duct of the rat were perfused in vitro, and the electrophysiological properties of the apical and basolateral membranes were examined with KCl-filled microelectrodes. The fractional resistance of the apical membrane (FRa = Ra/Ra + Rbl) and the transepithelial resistance (RT) were estimated by cable analysis. In control tubules the transepithelial voltage (VT) averaged -2.2 mV, and the voltage across the basolateral membrane (Vbl) averaged -51.1 mV. RT was 11.9 k omega.cm (72.8 omega.cm2), and FRa was 0.94. Pretreatment of the rats with deoxycorticosterone (DOC)-pivalate for 7-10 days did not alter these electrophysiological properties. In control tubules, amiloride in the lumen (10(-5) M) changed VT from -3.0 to +1.4 mV and increased Vbl from -49.4 to -53.8 mV, RT from 12.5 to 13.6 k omega.cm, and FRa from 0.92 to 0.98. Thus the apical membrane is conductive to Na+. An increase of the bath K+ concentration from 4 to 15 mM caused an 18.8 mV depolarization of Vbl: barium in the bath also depolarized Vbl. A fivefold decrease in the [HCO3-] in the bath depolarized Vbl by 13.1 mV. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) blocked this depolarization. Thus the basolateral membrane is conductive to K+ and HCO3-. Experiments with ouabain revealed a Na+-K+-ATPase in the basolateral membrane. Taken together, the results support a model in which electrogenic Na+ absorption is driven by the Na+-K+-ATPase in the basolateral membrane, with passive movement of Na+ occurring through an amiloride-sensitive conductive pathway in the apical membrane.
Renal ischemia and reperfusion impair endothelium-dependent vascular relaxation
Authors: Lieberthal W. , Wolf E. F. , Rennke H. G. , Valeri C. R. , Levinsky N. G.
Published: December 2017

We studied the hemodynamic response of the isolated erythrocyte-perfused kidney to 25 min of ischemia and found that renal vascular resistance (RVR) was increased in the reflow period (16.7 +/- 1.4 mmHg.ml-1.min.g following ischemia vs. 10.2 +/- 0.8 mmHg.ml-1.min.g in control kidneys). Endothelial independent vasodilators [atrial natriuretic factor (ANF) and sodium nitroprusside] prevented the increase in RVR that occurred after ischemia. In contrast, acetylcholine and the calcium ionophore A23187, two vasodilators that act by releasing endothelium-derived relaxing factor (EDRF), had no effect on the increased RVR that occurs on reflow. Two inhibitors of EDRF, methylene blue and gossypol, increased RVR in nonischemic kidneys by 45 +/- 6 and 46 +/- 11%, respectively, an increase that was comparable to that found with ischemia alone (55 +/- 7%). The increase in RVR found with the combination of EDRF inhibition and ischemia (59 +/- 5%) was the same as that found with ischemia alone. We conclude that EDRF activity is impaired following ischemia and reperfusion. This abnormality in EDRF may be an important mechanism contributing to postischemic vasoconstriction in the renal vasculature.
Acetazolamide inhibits acidification by the turtle bladder independent of cell pH
Authors: Graber M. , Dixon T. , Coachman D. , Devine P.
Published: December 2017

Acetazolamide (ACZL) inhibits luminal acidification by the turtle urinary bladder, a process thought to be mediated by the drug's ability to inhibit carbonic anhydrase (CA) and thus elevate cell pH. To test the hypothesis that these transport changes are actually mediated by changes of cell pH, we measured this parameter in single, identifiable mucosal cells using 4-methylumbelliferone and fluorescence microscopy. In control bladders 5 X 10(-4) M ACZL inhibited proton transport by 80 +/- 6%, and alkalinized cell pH, especially in a subpopulation of CA cells. A much larger cell alkalinization was induced by serosal HCO3- but proton transport fell only 30 +/- 7%. When cell pH was clamped at approximately 7.0 using 50 mM dimethyloxazolidinedione, or when cell pH was acidified using 7.5 mM propionate, transport rates still declined by 74 +/- 2, and 100 +/- 12%, respectively, in response to ACZL. In propionate-acidified bladders, 1 mM sodium azide blocked the inhibition of transport seen with 5 X 10(-4) M ACZL and reversed the inhibition with 10(-5) M ACZL. The apical endocytosis rate was increased by ACZL in normal and propionate-acidified bladders, but was not stimulated by alkalinizing the cell with NH4Cl. We conclude that ACZL can induce cellular alkalinization in this tissue, but that this pH change is not required for the inhibition of transport, or the ACZL-associated stimulation of endocytosis. The drug's ability to inhibit acidification appears to be the result of an azide-sensitive mechanism that has yet to be defined.
Role of renal nerves in control of sodium excretion in chronic congestive heart failure
Authors: Mizelle H. L. , Hall J. E. , Montani J. P.
Published: December 2017

The aim of this study was to examine the contribution of the renal nerves to the sodium retention in chronic congestive heart failure produced by rapid ventricular pacing. In 10 female dogs the left kidney was denervated and the urinary bladder was split to allow separate 24-h urine collection from an innervated and a denervated kidney in the same dog. The dogs were placed on an 80-meq/day sodium intake and permitted to recover for at least 2 wk. Control measurements were made for 5 days followed by ventricular pacing at 270-300 beats/min for 6 days. Cardiac output (CO), measured with an electromagnetic flow probe around the ascending aorta, fell from a control of 2.4 +/- 0.3 to 1.4 +/- 0.2 l/min (6 day average) during pacing while mean arterial pressure (MAP) fell from 91 +/- 4 to 71 +/- 3 mmHg. In six dogs, sodium excretion fell to an average of less than 2 meq/day (80 meq/day intake) during the 6-day pacing period in both the innervated and denervated kidneys. In four dogs, sodium excretion returned back toward control on days 3-6 of pacing despite sustained reductions in CO and MAP. However, there were no differences in renal hemodynamics or electrolyte excretion between innervated and denervated kidneys in either the compensated or decompensated dogs. These results suggest that other control mechanisms, besides the renal nerves, are primarily responsible for the sodium retention in this model of chronic congestive heart failure.
Inhibition of rat mesangial cell mitogenesis by nitric oxide-generating vasodilators
Authors: Garg U. C. , Hassid A.
Published: December 2017

Recent studies indicate that endothelium-derived relaxing factor (EDRF) may be identical with nitric oxide (NO). The purpose of this study was to investigate the antimitogenic effect of NO-generating drugs in cultured mesangial cells. S-nitroso-N-acetylpenicillamine, sodium nitroprusside, and isosorbide dinitrate, which generate NO, dose dependently inhibited serum-stimulated DNA synthesis. All three drugs also inhibited the rate of cell proliferation, whereas sodium nitroprusside and S-nitroso-N-acetylpenicillamine decreased cell density at confluence. The antimitogenic activity of S-nitroso-N-acetylpenicillamine was labile in culture medium and could be inhibited by hemoglobin, supporting the view that NO, in free or bound form, was the ultimate effector. All three vasodilators increased cellular guanosine 3',5'-cyclic monophosphate (cGMP) levels dose dependently; moreover, 8-bromo-cGMP mimicked the effects of the NO-generating drugs, suggesting that cGMP may be an intracellular mediator of antimitogenesis. The growth-inhibitory effect of S-nitroso-N-acetylpenicillamine was reversible and was not due to cell toxicity as shown by several criteria of cell viability. The results raise the possibility that EDRF/NO may be a modulator of mesangial cell growth in vivo.
Sodium transfer from endolymph through a luminal amiloride-sensitive channel
Authors: Ferrary E. , Bernard C. , Oudar O. , Sterkers O. , Amiel C.
Published: December 2017

An in vitro preparation of frog semicircular canal was devised to study the mechanisms of Na transport across the labyrinthine epithelium. When the lumen of the semicircular canal was filled with perilymph-like solution, the structure was able to secrete K into and to absorb Na from the lumen and to generate a lumen-positive transepithelial potential. When the lumen of the semicircular canal was filled with endolymph-like solution, the electrochemical composition of the luminal fluid was partly maintained up to 2 h. In this last experimental condition net and unidirectional fluxes were calculated in absence or presence of transport inhibitors, separately for the ampulla and for the nonampullar part of the canal. Amiloride (10(-5) M) but not dimethyl amiloride (10(-5) M) inhibited 60% of the unidirectional Na efflux out of endolymph; this Na efflux decrease resulted in an increase of the inward net Na flux. The net Na flux was also increased after abluminal application of ouabain (10(-3) M), furosemide (10(-4) M), and bumetanide (10(-6) M). This study validates this isolated preparation as a suitable tool for the study of endolymph secretion, confirms that the secretion of endolymph is achieved in the ampulla, and provides evidence for an apical amiloride-sensitive Na channel through which Na is transferred out of endolymph along an electrochemical gradient provided by the activity of the abluminal Na+-K+-ATPase.
Effect of renal interstitial infusion of arachidonic acid on proximal sodium reabsorption
Authors: Kinoshita Y. , Romero J. C. , Knox F. G.
Published: December 2017

The effect of prostaglandins (PGs) on proximal sodium reabsorption has not been fully defined. The objective of the present study was to determine the response of proximal tubular sodium reabsorption to infusions of arachidonic acid and specific PGs into the renal interstitium in rats. Renal interstitial infusions of arachidonic acid as well as the individual PGs, I2, E2, and F2 alpha, were employed to elevate the concentration of these PGs in the kidney. Infusion of 10(-4) M arachidonic acid elicited a marked increase of urinary excretion of 6-keto-PGF1 alpha (a stable metabolite of PGI2) from 260.1 +/- 52.7 to 507.4 +/- 129.5 pg/min (P less than 0.05) and a smaller increase of PGE2 from 18.4 +/- 11.2 to 25.9 +/- 10.9 pg/min (P less than 0.05). When micropuncture samples were obtained from superficial late proximal tubules, infusion of arachidonic acid increased the fractional delivery of sodium (FDNa) from 47.8 +/- 5.9 to 58.3 +/- 4.6% (n = 6, P less than 0.01). In the presence of indomethacin, arachidonic acid failed to augment FDNa. Infusion of 10(-5) M PGI2 also increased FDNa from 51.4 +/- 3.4 to 64.0 +/- 4.4% (n = 10, P less than 0.01). PGF2 alpha did not change FDNa and PGE2 decreased it from 53.1 +/- 5.4 to 37.4 +/- 3.3% (n = 8, P less than 0.01). In summary, the present study demonstrates that renal interstitial infusion of arachidonic acid decreases sodium reabsorption by the superficial proximal tubules possibly through the stimulation of PGI2 production.
Permissive role of dopamine in renal action of ANP in volume-expanded rats
Authors: Katoh T. , Sophasan S. , Kurokawa K.
Published: December 2017

A possible role of dopamine in the diuretic and natriuretic action of atrial natriuretic peptide (ANP) was evaluated in the rat. ANP was infused into the left renal artery of anesthetized rats whose kidneys were denervated. ANP both at 12 and 1.2 pmol/h caused immediate ipsilateral increases in urine volume (V), urine Na excretion (UNaV), and fractional excretion of Na (FENa). Ipsilateral glomerular filtration rate (GFR) and renal plasma flow (RPF) increased with 12 pmol/h ANP but not with 1.2 pmol/h ANP. Intravenous infusion of haloperidol, Sch-23390, or carbidopa markedly attenuated the increase in V, UNaV, and FENa with 12 pmol/h ANP and completely abolished the increases in GFR and RPF. Haloperidol, Sch-23390, and carbidopa also completely abolished the renal effects of 1.2 pmol/h ANP. In the presence of carbidopa, a small dose of dopamine infused into the systemic circulation, which by itself has no effects on blood pressure, V, GFR, RPF, and UNaV, restored the diuretic and natriuretic effects of ANP. In addition, an increase in urinary guanosine 3',5'-cyclic monophosphate by ANP was not affected by either haloperidol or carbidopa. These data indicate that dopamine may be necessary, as a permissive agent, for the renal effects of ANP to manifest and that the effects of dopamine may be independent of ANP-stimulated guanylate cyclase activation.
Membrane stretch: a physiological stimulator of Ca2+-activated K+ channels in thick ascending limb
Authors: Taniguchi J. , Guggino W. B.
Published: December 2017

The effects of membrane stretch on Ca2+-activated (maxi) K+ channels were examined in the apical membrane of cultured medullary thick ascending limb (MTAL) cells. Using cell-attached patchclamp technique, we found that negative pressure (-33 +/- 5 cmH2O) applied to the patch membrane increased fractional open probability (NPo) from 0.3 +/- 0.2 to 29.9 +/- 7.6% (n = 12) in the presence of 1.8 mM Ca2+ in the pipette. The activity returned to control on releasing the negative pressure. Reduction of extracellular osmolality from 293.2 +/- 1.6 to 219.8 +/- 1.1 mosmol/kg also activated K+ channels (NPo = 43.8 +/- 12.2%, n = 8) in cell-attached patches. Removal of Ca2+ from both pipette and bathing solution inhibited osmotic activation of K+ channels. K+ channels were shown to be Ca2+-activated K+ channels by their conductance (146 +/- 7 pS, n = 5) and Ca2+ dependence. Our data suggest that membrane stretch caused by swelling or possibly by tubular flow enhances Ca2+ entry across the apical cell membrane of MTAL cells activating maxi K+ channels.
Direct hemodynamic effect of insulin in the isolated perfused kidney
Authors: Cohen A. J. , McCarthy D. M. , Stoff J. S.
Published: December 2017

The hemodynamic effect of insulin was examined in isolated perfused kidneys. Experiments were designed to study the effect of the hormone on basal hemodynamics and in the presence of angiotensin II (ANG II). Physiological insulin concentrations caused both renal vasodilation and increased glomerular filtration rate (GFR) during basal perfusion periods and attenuated the vasoconstrictor action of ANG II while limiting the ANG II-induced reduction of GFR. Insulin also increased fractional sodium reabsorption and diminished the natriuretic effect of ANG II. The addition of insulin to perfusions in which ANG II was infused from the start caused renal vasodilation, although supraphysiological concentrations were required. Kidneys perfused with hyperoncotic albumin to prevent filtration similarly demonstrated a vasodilatory effect of insulin that did not require glomerular filtration. Inhibition of prostaglandin (PG) synthesis with indomethacin prevented the vasodilatory effects of insulin. These data support the hypothesis that insulin causes renal vasodilation by a PG-dependent process.
Direct Na+-K+ pump stimulation by K+ in cortical collecting tubules: a mechanism for early renal K+ adaptation
Authors: Fujii Y. , Katz A. I.
Published: December 2017

To evaluate the mechanism of increased Na+-K+ pump turnover rate that characterizes the early cortical collecting tubule (CCT) response to K+ loading [Y. Fujii, S. K. Mujais, and A. I. Katz. Am. J. Physiol. 256 (Renal Fluid Electrolyte Physiol. 25): F279-F284, 1989.], we measured ouabain-sensitive 86Rb+ uptake in microdissected rat CCT exposed acutely to elevated ambient K+ in vivo and in vitro. Tubules preincubated in 10 mM K+ had higher 86Rb+ uptake than when preincubated in 5 mM K+ (25.9 +/- 1.2 vs. 18.9 +/- 0.7 pmol.mm-1.min-1, P less than 0.001). KCl infusion (5 mumol.100 g-1.min-1 x 60 min) increased 86Rb+ uptake from 19.2 +/- 1.0 to 31.2 +/- 1.4 pmol.mm-1.min-1, P less than 0.001; the increment was preserved in tubules subsequently treated with monensin or nystatin in vitro, suggesting that pump stimulation was not mediated by increased cell Na+. This conclusion was confirmed in separate experiments in which the effect of K+ on 86Rb+ uptake was not altered by concurrent preincubation with amiloride. Studies with CCT from isolated perfused kidneys and from adrenalectomized animals revealed that stimulation of 86Rb+ uptake by a K+ load occurs rapidly (less than or equal to 5 min) and is independent of hormonal factors. Increased external K+ produces a rapid rise in K+-transporting capacity (turnover rate) of the Na+-K+ pump in CCT. This phenomenon probably represents a direct effect on K+ on the pump and is an important component of the early renal response to increased K+ secretory load.
Effects of beta-adrenergic stimulation with isoproterenol on glomerular hemodynamics
Authors: Pelayo J. C. , Tucker B. J. , Blantz R. C.
Published: December 2017

To evaluate the contribution of beta 1-2-adrenergic receptor stimulation to the regulation of single-nephron glomerular filtration rate (SNGFR), we examined by micropuncture techniques the effects of systemic and intrarenal infusion of isoproterenol on glomerular hemodynamics in plasma volume-expanded Munich-Wistar rats. Isoproterenol infused systemically was consistently associated with an elevation in glomerular capillary hydrostatic pressure difference (delta P) from 44.2 +/- 1.2 to 50.1 +/- 1.3 mmHg, P less than 0.01, the consequence of a 5.9-mmHg fall in Bowman's space hydrostatic pressure, P less than 0.005. The potentially beneficial effect of increased delta P on SNGFR was overcome by a 40% reduction in the glomerular ultrafiltration coefficient (LpA) from 0.043 +/- 0.003 to 0.026 +/- 0.003 nl.s-1.mmHg-1.g kidney wt-1, P less than 0.005, with a net effect of a modest 13% decline in SNGFR, P less than 0.01. In contrast, the intrarenal infusion of isoproterenol did not modify glomerular hemodynamics. Suppression of angiotensin II activity eliminated the influences of systemic isoproterenol infusion on LpA and delta P, the latter was the consequence of lower efferent arteriolar resistance. The findings suggest that systemic infusion of a beta 1-2-adrenergic agonist results in a decrease in LpA via angiotensin II effects and exerts a vasodilatory action on postglomerular vessels during angiotensin II inhibition.
Continuous-flow quantitation of Na+ and K+ in nanoliter samples using chromogenic macrocyclic ionophores
Authors: Terada Y. , Knepper M. A.
Published: December 2017

Continuous-flow colorimetric methods for measurement of sodium and potassium contents in 1- to 30-nl aqueous samples are described. The methods employ macrocyclic ionophores (cryptahemispherands) that selectively bind sodium or potassium, altering the absorbance spectra of covalently attached chromophores. The potassium method is linear in the range 0-350 pmol and exhibits a high degree of precision (coefficient of variation of approximately 2% in the 150- to 350-pmol range). It can detect as little as 8 pmol of K+. The sodium method is linear in the range 0-2,700 pmol and also exhibits a high degree of precision (coefficient of variation of approximately 3% in the 1,700- to 2,700-pmol range). It can detect as little as 57 pmol of Na+. The instrumentation and reagents are available from commercial sources. These methods are proposed for measurement of K+ and Na+ fluxes in isolated perfused tubules.
Effects of glucagon on H(+)-HCO3- transport in Henle's loop, distal tubule, and collecting ducts in the rat
Authors: Mercier O. , Bichara M. , Delahousse M. , Prigent A. , Leviel F. , Paillard M.
Published: December 2017

Paired micropuncture experiments were carried out in somatostatin-infused volume-expanded rats to examine the effects of a glucagon infusion (0.05 ng.min-1.g body wt-1) on urinary acidification and tubular handling of bicarbonate. Whole kidney and single-nephron glomerular filtration rate were not affected by glucagon. In thyroparathyroidectomized (TPTX) rats, glucagon inhibited the reabsorption of total CO2 in Henle's loop. In intact animals, however, the latter effect was not observed. In the distal tubule accessible to micropuncture, net total CO2 absorption was observed during volume expansion plus somatostatin infusion, which reversed to net total CO2 secretion during glucagon infusion in Wistar rats; thus the late distal delivery of total CO2 increased almost 80%. Marked inhibition of urinary acidification occurred in all animals as evidenced by a rise in urine pH and bicarbonate excretion. Conversely, a somatostatin infusion, which decreased the plasma glucagon concentration, stimulated net total CO2 absorption along the distal tubule and augmented final urine acidification in Wistar rats. Finally, urine-minus-blood PCO2 during alkaline diuresis was significantly reduced by glucagon infusion in bicarbonate-loaded TPTX rats. We conclude that 1) glucagon inhibits bicarbonate absorption in superficial Henle's loop in TPTX but not in intact rats, and 2) glucagon stimulates bicarbonate secretion and/or inhibits proton secretion in the distal tubule and collecting ducts, which leads to reduced urinary acidification.
NBD-taurine uptake by alpha-type carbonic anhydrase cells of turtle bladder
Authors: Palmisano J. , Mitchell P. P. , Steinmetz P. R.
Published: December 2017

The uptake of the fluorescent anion, N-(7-nitrobenz-2-oxa-1,3 diazol-4-yl)aminoethanosulfonic acid-taurine (NBD-T) was examined in sheets of turtle bladder epithelial cells after either serosal or mucosal exposure to the fluorescent anion. Serosal uptake of NBD-T into a population of epithelial cells was demonstrated in thin epithelial sheets scraped from bladder sacs exposed to low (0.5 mM) concentrations of NBD-T sufficient to cause fluorescence in turtle erythrocytes. In nine sheets NBD-T fluorescence was observed in 14.4 +/- 1.3% of epithelial cells; by phase-contrast microscopy of the same fields, these cells were nongranular or carbonic anhydrase (CA) cells. An additional 8.1 +/- 1.0% of cells was nongranular, but failed to exhibit fluorescence after serosal NBD-T exposure, consistent with a beta-CA cell population. Apical uptake of NBD-T into epithelial cells was demonstrable only at high (5 mM) mucosal concentrations in both thin sheets and superfused bladder segments. In thin sheets, NBD-T fluorescence was observed in 15.8 +/- 0.7% of cells and appeared to have a punctate subapical distribution; phase-contrast of the same fields (n = 46) revealed a nongranular cell population of 21.9 +/- 0.9%. Nongranular cells corresponded closely to CA cells as identified with carboxyfluorescein fluorescence. Hence, apical NBD-T was taken up primarily by alpha-CA cells. In conclusion, NBD-T is transported by alpha-CA cells either across the basolateral membrane with high affinity comparable to that of turtle red cell band 3 protein or across the apical membrane with low affinity via a less-specific mechanism such as endocytosis.(ABSTRACT TRUNCATED AT 250 WORDS)
Phorbol myristate acetate inhibits acidification by turtle urinary bladder
Authors: Graber M. , Devine P. , Dixon T.
Published: December 2017

The effects of phorbol myristate acetate (PMA) on acid secretion by the turtle urinary bladder were examined to evaluate the importance of protein phosphorylation in modulating the distal acidification system. In HCO3-free PO4 buffer 0.2 mM mucosal PMA inhibited reverse short-circuit current (RSCC) by 42%. The inhibition of RSCC was dose dependent, and RSCC approached zero at high concentrations of PMA. PMA also inhibited acid secretion measured titrimetrically but had no effect on RSCC from bladders in which proton secretion was selectively inhibited by an adverse pH gradient or serosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. The inhibition by PMA was duplicated by 1-oleoyl-2-acetyl-rac-glycerol, but not by an inactive phorbol ester. The PMA inhibition was much more potent with mucosal compared with serosal application. The PMA inhibition caused a significant 0.15 pH unit reduction of carbonic anhydrase (CA) cell cytoplasmic pH and a change in the CA cell morphology. Unlike the inhibition of proton transport induced by acetazolamide, the PMA inhibition was neither reversed nor prevented by sodium azide. We conclude that PMA decreases basal acid secretion and blocks the stimulatory effects of CO2 by an azide-insensitive mechanism distinct from that of acetazolamide. In view of recent findings that PMA stimulates HCO3 secretion by the turtle bladder, these results suggest that kinase C-mediated protein phosphorylation may be a central event in the transition from the secretion of acid to the secretion of base.
Unmasking sensitive alpha 2-adrenoceptor-mediated renal vasoconstriction in conscious rats
Authors: Wolff D. W. , Colindres R. E. , Strandhoy J. W.
Published: December 2017

Renal vascular reactivity to intrarenal arterial boluses of norepinephrine (NE), phenylephrine (PHE; alpha 1-agonist), and guanabenz (GBZ; alpha 2-agonist) was assessed in conscious, freely moving, chronically instrumented, normotensive Wistar rats. Dose-response curves (DRCs) were obtained in the absence and cumulative presence of propranolol (PROP; beta-antagonist), corynanthine (CORY; alpha 1-antagonist) and idazoxan (IDX; alpha 2-antagonist) to estimate effective dosages (ED) required for 15 and 75% peak reductions in renal blood flow. The PHE DRC had a short shallow ED15 region, but was primarily linear with a steep slope. The GBZ DRC had a shallow slope. The NE DRC had a prolonged shallow phase in the ED15 region and a steep slope in the ED75 region. PROP had no effect on the DRCs. CORY caused a parallel rightward shift of the PHE DRC and had no effect on the GBZ DRC. After CORY, the shallow ED15 portion of the NE DRC was even more pronounced with a slope now identical to that of the GBZ DRC, whereas the ED75 region of the NE DRC was shifted rightward like the PHE DRC. IDX preferentially antagonized the ED15 regions of the GBZ and NE DRCs. In a second group of rats, the alpha 2-adrenoceptor antagonist, rauwolscine, was administered following base-line DRCs to demonstrate rightward shifts of the NE and GBZ DRCs when PHE DRCs remained unaffected. Therefore, when boluses of NE are injected into the rat kidney, the vasoconstrictive responses are a result of the activation of both alpha 1- and alpha 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcitonin gene-related peptide: effects on renal arteriolar tone and tubular cAMP levels
Authors: Edwards R. M. , Trizna W.
Published: December 2017

The effects of calcitonin gene-related peptide (CGRP) and salmon calcitonin (SCT) on isolated afferent and efferent arteriolar tone and on adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in isolated tubules from rabbit kidney were compared. By themselves, CGRP and SCT had no effect on arteriole diameter. In norepinephrine-contracted afferent arterioles, CGRP, but not SCT, produced a concentration-dependent relaxation [50% maximal dose, (EC50) = 1.3 nM]. In contrast, neither CGRP nor SCT had any effect on efferent arterioles precontracted with norepinephrine or angiotensin II. CGRP, but not SCT, stimulated cAMP accumulation in glomeruli (EC50 = 0.5 nM). In tubules, CGRP increased cAMP levels only in SCT-responsive segments, e.g., cortical and medullary thick ascending limbs and distal convoluted tubules. In the medullary thick ascending limb, CGRP was approximately 500-fold less potent than SCT in stimulating cAMP accumulation with EC50s of 0.22 microM and 0.41 nM, respectively. The effect of maximum concentrations (1 microM) of CGRP and SCT on cAMP levels in the medullary thick ascending limb were not additive. The results suggest that there are specific CGRP receptors on afferent arterioles that produce relaxation and in glomeruli that are associated with an increase in cAMP production. In tubules, CGRP appears to be a weak agonist at the SCT receptor. We conclude that CGRP may play a role in the regulation of renal hemodynamics.
Differing actions of dietary protein and enalapril on renal function and proteinuria
Authors: Hutchison F. N. , Martin V. I. , Jones H. , Kaysen G. A.
Published: December 2017

Albuminuria (UalbV) increases in proportion to dietary protein in rats with passive Heymann nephritis. To determine whether a similar relationship existed in normal animals, 14 normal rats were switched from an 8.5% protein diet (LP) to a 40% protein diet (HP). Initially UalbV and glomerular filtration rate (GFR) increased in parallel, but GFR ceased to increase after 48 h while UalbV continued to increase, causing a significant increase in fractional renal clearance of albumin (FCalb). In contrast, HP for 4 days caused only a transient increase in GFR in nephrotic rats but effected a threefold sustained increase in UalbV. Pretreatment of nephrotic rats with enalapril blunted but did not entirely prevent the increase in UalbV after switching to HP and did not affect the increase or subsequent decline in GFR. Treatment with enalapril for 10 days reduced UalbV and FCalb in nephrotic rats fed either LP or HP. The similar pattern of changes in urinary albumin excretion in normal and nephrotic rats after dietary protein augmentation suggests that dietary protein may modify UalbV by the same process in both normal and nephrotic animals. The increases in UalbV and GFR resulting from dietary protein augmentation represent parallel but independent processes, since only the proteinuric response is modified by converting enzyme inhibition. Dietary protein restriction and converting enzyme inhibition exert an additive effect to reduce UalbV.
Glomerular hemodynamic alterations during renal nerve stimulation in rats on high- and low-salt diets
Authors: Tucker B. J. , Peterson O. W. , Munger K. A. , Bird J. E. , Mitchell M. , Pelayo J. C. , Blantz R. C.
Published: December 2017

Renal adrenergic nerve activity exerts a major influence on glomerular hemodynamics and tubular fluid reabsorption. Modulation of the functional expression of adrenergic activity in the kidney can be mediated, in part, by the renin-angiotensin system and by prostanoid activity. Alterations in dietary salt intake have been previously shown to modify the activity of various vasoactive systems, including angiotensin and prostaglandin activity and thereby have a potential of modifying the glomerular hemodynamic response to a given renal adrenergic stimulus. Munich-Wistar rats were fed either a high-, low-, or normal salt diet for 2 wk before the day of the study. Measurements of glomerular hemodynamics were performed in both unstimulated with basal renal nerve traffic eliminated and during exogenous renal nerve stimulation (RNS) (3 Hz). RNS decreased glomerular capillary hydrostatic pressure and single-nephron plasma flow to a similar extent in all three dietary conditions via increases in afferent arteriolar resistance. The data demonstrated that dietary preconditioning does not alter the glomerular hemodynamic response to an exogenous, fixed RNS. Glomerular prostaglandin E2 production and plasma renin activity were significantly greater in rats fed a low-salt diet compared with either normal- or high-salt diet. The constancy of glomerular hemodynamic responses to RNS in spite of wide variations in dietary salt intake indicates that functional renal hemodynamic differences observed as a result of NaCl intake must be primarily the consequence of differences in renal nerve traffic and not hormonal alterations.
Collecting tubule adaptation to respiratory acidosis induced in vivo
Authors: Laski M. E. , Kurtzman N. A.
Published: December 2017

To examine the effects of respiratory acidosis in vivo on the adaptation of acidification in the collecting tubule, New Zealand White rabbits were exposed to a 6.7% CO2-93.3% O2 gas mixture in an environmental chamber for 0, 6, 24, or 48 h before obtaining collecting tubules for in vitro study. These collecting tubules were then perfused and bathed in vitro in identical Krebs-Ringer bicarbonate solutions. After 1 h equilibration total CO2 flux (JtCO2) was measured. The urine pH of the rabbits fell, whereas the blood bicarbonate rose as CO2 exposure time increased. In cortical collecting tubules, JtCO2 in vitro correlated with length of animal exposure to hypercarbia (y = 1.14174 + 0.1437x, r = 0.57, P = 0.002), and with the blood bicarbonate of the animal (y = 26.8471 + 0.0858x, r = 0.59, P less than 0.05). In vitro JtCO2 in medullary collecting tubules from rabbits that had been in hypercarbic atmosphere for 48 h (23.2 +/- 4.9 pmol.mm-1.min-1) did not differ from JtCO2 in control tubules (25.0 +/- 3.2 pmol.mm-1.min-1, not significant). Thus the cortical collecting tubule exhibits an adaptive increase in JtCO2 in response to hypercarbia, whereas the medullary collecting tubule does not.
Brain pH in acute isocapnic metabolic acidosis and hypoxia: a 31P-nuclear magnetic resonance study
Authors: Adler S. , Simplaceanu V. , Ho C.
Published: December 2017

It is well known that brain pH changes rapidly in acute hypercapnia or hypocapnia. The effect of acute isocapnic metabolic acid-base change on brain pH is less certain. To study this problem, acute isocapnic metabolic acidosis was induced by HCl or lactic acid infusions in rats, and recovery from acidosis was accomplished by NaHCO3 infusion. Brain pH was measured by 31P-nuclear magnetic resonance. Despite decreases in blood pH of 0.34 and 0.36 units, respectively, in less than 1 h of acid infusion and rapid recovery during bicarbonate infusion, brain pH was unaffected (ranging between 7.08 and 7.11) and was uncorrelated with blood pH. The blood pH minus brain pH gradient was eliminated by the acidosis. By contrast, hypoxia-induced endogenous lactic acidosis lowered blood and brain pH equivalently, but the fall in brain pH preceded that in blood. During normoxic recovery, brain pH overshot and became alkaline when blood pH was still significantly reduced and blood lactate levels were markedly elevated. Presumably, this is due to stimulated active H+ transport. The results demonstrate that brain pH is affected differently in metabolic, respiratory, and endogenous acid-base disturbances. Thus brain pH cannot be predicted solely from blood pH values.
Cardiovascular and renal actions of endothelin: effects of calcium-channel blockers
Authors: Cao L. Q. , Banks R. O.
Published: December 2017

We have evaluated the effects of two calcium-channel blockers, verapamil (VP) and manganese (Mn), on endothelin (EN)-induced changes in systemic and renal function in pentobarbital sodium-anesthetized female rats and male and female dogs. In the rat studies, saline was infused at 24 microliters/min iv with or without (n = 10) two doses of VP (0.02 mg.kg-1.min-1, n = 5; 0.03 mg.kg-1.min-1, n = 3) or Mn (0.5 mg.kg-1.min-1, n = 5) throughout the entire experiment. After surgery, rats were allowed 60 min to stabilize, and three 20-min control clearances were collected. EN (100 ng.kg-1.min-1) was then added to the infusate for 30 min. EN alone caused an increase in mean arterial pressure (MAP) and a decrease in the glomerular filtration rate (GFR). VP at either dose and Mn totally blocked the EN-induced increase in MAP. However, the two calcium-channel blockers had no effect on the renal action of EN; the GFR (in ml/min) decreased (at 30 min of EN infusion) from 2.7 +/- 0.1 (SE) to 0.7 +/- 0.1 (P less than 0.01) in controls, from 2.5 +/- 0.3 to 0.4 +/- 0.3 with the lower dose of VP (P less than 0.01), from 2.3 +/- 0.1 to 0.6 +/- 0.2 with the higher dose of VP (P less than 0.01), and from 1.5 +/- 0.5 to 0.9 +/- 0.6 with Mn (P less than 0.05). Infusion of EN alone (10 ng.kg-1.min-1, n = 5) and EN with VP (50 micrograms/min, n = 3) into the renal artery of dogs reduced renal blood flow from 3.5 +/- 0.4 to 0.9 +/- 0.2 and from 3.6 +/- 0.6 to 1.2 +/- 0.6 ml.g-1.min-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
NEM-sensitive ATPase activity in rat nephron: effect of metabolic acidosis and alkalosis
Authors: Sabatini S. , Laski M. E. , Kurtzman N. A.
Published: December 2017

The present study was designed to quantitate the amount and to map the localization of N-ethylmaleimide (NEM)-sensitive adenosinetriphosphatase (ATPase) activity in microdissected segments of the rat nephron. After complete nephron mapping the effect of chronic metabolic acidosis and alkalosis on enzyme activity was determined. In control animals the highest enzyme activity was found in the early proximal convoluted tubule of juxtamedullary nephrons; superficial early proximal tubule as well as medullary and cortical thick ascending limbs and collecting ducts also contained substantial activity. Enzyme activity in the papillary collecting duct before entry into the ducts of Bellini was 329 +/- 93 pmol.mm-1.h-1 (n = 8); after entry, however, enzyme activity was approximately one-fourth that value (60 +/- 9 pmol.mm-1.h-1, n = 8, P less than 0.01). No NEM-sensitive ATPase activity was found in the thin limbs of the loop of Henle. Enzyme activity increased in both the medullary and cortical thick ascending limbs as well as in the cortical collecting tubule in response to NH4Cl-induced chronic metabolic acidosis; in the cortical collecting duct, metabolic acidosis increased maximum activity (Vmax) but did not change Michaelis-Menten constant (Km). In the proximal convoluted tubule, enzyme activity decreased with metabolic acidosis. Bicarbonate loading had no effect on enzyme activity except in the most distal portion of the collecting duct where it was stimulated. These results show that NEM-sensitive ATPase activity exists throughout much of the rat nephron. These data suggest that both the cortical collecting tubule and thick ascending limb are regulatory sites of distal urinary acidification during acid loading.
Role of hormonal factors in plasma K alterations in acute respiratory and metabolic alkalosis in dogs
Authors: Suzuki H. , Hishida A. , Ohishi K. , Kimura M. , Honda N.
Published: December 2017

Studies were performed on previously nephrectomized dogs to examine roles of hormonal factors in plasma potassium alterations in acute alkalosis. Respiratory and metabolic alkalosis were induced by hyperventilation and intravenous NaHCO3 or tris(hydroxymethyl)aminomethane (Tris) infusion, respectively. Respiratory and NaHCO3-induced alkalosis provoked decreases in plasma potassium from the control value of 5.12 +/- 0.68 (SE) to 4.21 +/- 0.55 meq/l (P less than 0.01) and from 4.65 +/- 0.26 to 3.91 +/- 0.16 meq/l (P less than 0.01) within 180 min, respectively. In contrast, Tris-induced alkalosis elicited an increase in plasma potassium from the control value of 4.56 +/- 0.30 to 5.31 +/- 0.30 meq/l (P less than 0.01). Hypokalemia in respiratory alkalosis was associated with a decrease in the plasma norepinephrine concentration from the control level of 377 +/- 104 to 155 +/- 41 pg/ml (P less than 0.05) but not with changes in plasma levels of epinephrine, insulin, glucagon, cortisol, and aldosterone. However, this hypokalemia was not affected by phentolamine. Also, somatostatin did not modify the hypokalemic response. NaHCO3-induced hypokalemia was associated with a decline in the plasma aldosterone and norepinephrine concentrations. The decline in plasma norepinephrine in NaHCO3-induced alkalosis followed the decrease in plasma potassium. In Tris-induced alkalosis, plasma insulin increased but norepinephrine decreased. The findings do not suggest fundamental roles of the hormonal factors in the plasma potassium alterations in bilaterally nephrectomized dogs with acute alkalosis.
Membrane crosstalk in the mammalian proximal tubule during alterations in transepithelial sodium transport
Authors: Lapointe J. Y. , Garneau L. , Bell P. D. , Cardinal J.
Published: December 2017

The present paper examines the effects of reduced transepithelial Na transport (JNa) on membrane electrophysiological parameters in proximal convoluted tubules and the possible role of cytosolic calcium concentration ([Ca]i) in the regulation of basolateral membrane K conductance (GK). When JNa was reduced by elimination of glucose and alanine and replacement of 100 mM sodium with N-methyl-D-glucamine from the luminal perfusate, basolateral membrane potential (VBL) hyperpolarized transiently by 12.6 mV and the ratio of apical to basolateral membrane resistance (RA/RBL) doubled. The apparent transference number for K at the basolateral membrane (GK/Gcell) decreased from 0.13 to 0.08 in the first 4 min following reductions in JNa. The elimination of Na-alanine and Na-glucose cotransport was responsible for the initial hyperpolarization and increase in RA/RBL, whereas the resultant decrease in the cellular concentrations of glucose and alanine, together with the reductions in GK, could elicit the secondary VBL depolarization. Measurement of [Ca]i with the fluorescent probe fura-2 during reductions in JNa revealed that [Ca]i increased by an average of 12%, a value very similar to the average reduction in cellular volume (13%) measured using morphometric techniques. The observation that [Ca]i increased while GK was decreasing is inconsistent with the effect of [Ca]i on putative basolateral Ca-activated K channel. We believe that [Ca]i changes passively (at least in the first few minutes) in response to a decrease in cell volume occurring as a consequence of reductions in JNa and that some as yet unidentified volume-sensitive mechanism is responsible for the regulation of GK.
Sympathetic modulation of renal autoregulation by carotid occlusion in conscious dogs
Authors: Persson P. B. , Ehmke H. , Nafz B. , Kirchheim H. R.
Published: December 2017

The effects of a moderate reflex activation of the sympathetic nervous system on renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in 29 experiments on seven conscious foxhounds. Autoregulation parameters were derived by a stepwise reduction of renal artery pressure of 10-mmHg decrements. An occlusion of both common carotid arteries (CCO) was used as a moderate sympathetic stimulus. This procedure did not influence the basal levels of RBF and GFR. However, the lower limits of autoregulation were considerably shifted (RBF, control 63 +/- 3 mmHg vs. CCO 91 +/- 8 mmHg, P less than 0.01; GFR, control 77 +/- 5 mmHg vs. CCO 102 +/- 5 mmHg, P less than 0.01). CCO also affected the rate by which RBF and GFR decreased below the autoregulatory range (subautoregulatory function: RBF, control y = 0.056x - 1.4 vs. CCO y = 0.037x - 0.9 ml.mmHg-1.g-1, P less than 0.05; GFR, control y = 0.0089x - 0.4 vs. CCO y = 0.0054x - 0.28 ml.mmHg-1.g-1, P less than 0.05). An alpha-blockade via intrarenal prazosin infusions markedly inhibited these effects of CCO. These findings demonstrate the failure of autoregulation below 102 mmHg for GFR and 91 mmHg for RBF during sympathetic activation, and they may be of clinical importance for situations that are characterized by a high sympathetic tone.
Angiotensin II control of the renal microcirculation in rats with reduced renal mass
Authors: Pelayo J. C. , Quan A. H. , Shanley P. F.
Published: December 2017

It has been suggested that angiotensin II (ANG II) activation after renal ablation contributes to the altered glomerular dynamics and proteinuria that characterizes this model of chronic renal failure. In the present study, male Munich-Wistar rats underwent 75% renal ablation (Nx group). Two weeks later, micropuncture studies were performed in sham-operated rats (sham group) and Nx group rats during intravenous infusion of either a vehicle or two ANG II inhibitors, namely [Sar1, Ala8]ANG II or MK-421 administered at a rate of 0.3 and 1 mg.kg body wt-1.h-1, respectively. Acute ANG II inhibition in sham group had no effect on mean arterial pressure (MAP), glomerular dynamics, or proteinuria. In contrast, in Nx group ANG II inhibition lessened glomerular hypertension (from 64.7 +/- 1.0 to 55.4 +/- 1.7 mmHg, P less than 0.0001) the result of postglomerular vasodilation (P less than 0.01), normalized the glomerular ultrafiltration coefficient (from 0.038 +/- 0.002 to 0.005 +/- 0.002 nl.s-1.mmHg-1, P less than 0.0001), and attenuated proteinuria (from 42.1 +/- 6.5 to 28.1 +/- 5.4 micrograms/min, P less than 0.01). MAP, single-nephron GFR and plasma flow were unaffected. These results suggest that ANG II activity is enhanced in nephrectomy, contributing in a major way to altered glomerular dynamics and proteinuria.
Inhibition of tubuloglomerular feedback during adenosine1 receptor blockade
Authors: Schnermann J. , Weihprecht H. , Briggs J. P.
Published: December 2017

Experiments were performed in anesthetized rats to study the effect of the selective adenosine1 (A1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) on tubuloglomerular feedback (TGF) responses assessed as the maximum change of stop-flow pressure (PSF). Compared with control, PSF responses were reduced during luminal application of CPX at 10(-4) and 10(-5)M (-4.9 +/- 0.44 vs. + 0.9 +/- 0.42 mmHg and -6.8 +/- 0.69 vs. -1.4 +/- 0.7 mmHg, respectively), during peritubular administration of CPX at 10(-4)M (-6.2 +/- 0.44 vs. -2.8 +/- 0.42 mmHg), and during infusion of CPX at 10(-4) M into the lumen of a neighboring nephron (-5.6 +/- 0.6 vs. -1.98 +/- 0.51 mmHg). Selectivity of CPX was tested by studying its effect on the PSF reduction produced by the A1-receptor agonist N6-cyclohexyladenosine (CHA). CHA at 10(-5)M reduced PSF when infused into the peritubular blood (-11.8 +/- 3.7 mmHg), and this effect was blunted by luminal application of CPX (-1.5 +/- 0.6 mmHg). CHA also reduced PSF when infused into a neighboring nephron, and this effect was blunted by infusing CPX at 10(-4)M into the same neighboring nephron, a different neighboring nephron, or a peritubular capillary. These results are consistent with the concept that activation of A1-receptors on vascular cells of the afferent arterioles participates in the mediation of TGF responses.