Kidney function and sodium handling in the pregnant spontaneously hypertensive rat.

Effects of gestation on volume homeostasis and renal function were studied in awake spontaneously hypertensive rats (SHR). Systolic blood pressure was similar to that of virgin littermates during most of SHR pregnancy but decreased near term (p less than 0.005). Plasma renin activity was lower in SHR than in age-matched Wistar-Kyoto (WKY) rats (p less than 0.001), but values were similar in gravid and nonpregnant animals from each strain. Renal renin content and lipid volume fractions of papillary interstitial granules were significantly greater in pregnant animal of each strain and those of the gravid WKY were also greater than both pregnant and virgin SHR. Saralasin had no effect on mean arterial pressure in gravid and virgin rats from either group. Plasma volume increased significantly near term in animals of both strains. Kidney weight, glomerular filtration rate (GFR), and renal blood flow were lower in SHR compared to WKY, and the hypertensive rats failed to demonstrate an increase in GFR during gestation, unlike the WKY. All SHR and pregnant WKY excreted infused sodium better than the virgin WKY. Also, regular Wistar animals excreted a salt load better than the virgin WKY. Finally, uterine blood flow, pup number and conceptus weight were similar in SHR and WKY. We conclude that pregnancy induces a decrease in blood pressure in SHR, and that angiotensin II does not seem to play an important role in maintaining blood pressure during gestation in either SHR or WKY. Despite a lower GFR and its failure to increase during pregnancy, renal sodium handling is not impaired in the SHR. The virgin WKY has a decreased ability to excrete sodium which is ameliorated during gestation.

Basic mechanisms of urinary acidification.

This article has examined the process of urinary acidification from the perspective of events occurring at the cellular and single nephron level. Accordingly, the reabsorption of filtered HCO3- and the titration of urine buffers can be ascribed to the fundamental process of H+ secretion. The precise mechanism of H+ secretion by the tubule cells, the rate by which this occurs, and the factors regulating transport differ between nephron segments. Despite these differences, the cellular process of urinary acidification can be viewed as the extrusion of H+ against an electrochemical gradient across the luminal cell membrane and the movement of an HCO3- equivalent across the basolateral cell membrane. In the proximal tubule (convoluted and straight portions) approximately 90 per cent of the filtered load of HCO3- is reabsorbed. This occurs without the development of large lumen-to-blood pH gradients. The secretion of H+ across the luminal membrane occurs primarily via an electrically neutral Na-H exchange mechanism. Since it is the lumen-to-cell Na+ gradient which provides the energy, the secretion of H+ is a "secondary active" process dependent on the function of the Na-K-ATPase located in the basolateral cell membrane. During the elaboration of an acid urine, the distal nephron (distal convoluted tubule and collecting duct) reabsorbs that portion of the filtered HCO3- escaping proximal reabsorption, titrates luminal buffers, and lowers urine pH. The secretion of H+ occurs by a "primary active" mechanism, which involves the extrusion of H+ across the luminal cell membrane by an electrogenic H+ pump driven by the hydrolysis of ATP. The rate at which H+ is secreted depends on the electrochemical gradient for H+ across the luminal membrane. Thus, changes in both lumen pH and potential will effect H+ secretion, with low lumen pH inhibiting transport and large lumen-negative potentials stimulating transport. In some animals, depending on their homeostatic needs, secretion of HCO3- by the distal nephron can also occur. This process is localized to the distal convoluted tubule and the cortical collecting duct and appears to represent a transport system distinct from that responsible for H+ secretion.

Continuing medical education: a new vision of the professional development of physicians.

The authors describe their vision of what continuing medical education (CME) should become in the changing health care environment. They first discuss six types of literature (e.g., concerning learning and adult development principles, problem-based/practice-based learning, and other topics) that contribute to ways of thinking about and understanding CME. They then state their view that the Association of American Medical Colleges (AAMC) has made a commitment to helping CME be more effective in the professional development of physicians. In presenting their new vision of CME, the authors describe their interpretation of the nature and values of CME (e.g., optimal CME is highly self-directed; the selection and design of the most relevant CME is based on data from each physician's responsibilities and performance; etc.). They then present seven action steps, suggestions to begin them, and the institutions and organizations they believe should carry them out, and recommend that the AAMC play a major role in supporting activities to carry out these steps. (For example, one action step is the generation and application of new knowledge about how and why physicians learn, select best practices, and change their behaviors). Six core competencies for CME educators are defined. The authors conclude by stating that collaboration among the appropriate academic groups, professional associations, and health care institutions, with leadership from the AAMC, is essential to create the best learning systems for the professional development of physicians.

Conductive properties of the rabbit outer medullary collecting duct: inner stripe.

Segments of outer medullary collecting duct were dissected from the inner stripe of the rabbit kidney (OMCDi) and perfused in vitro. The conductive properties of the tubule epithelium and individual cell membranes were determined by means of cable analysis and intracellular voltage-recording microelectrodes. In 35 tubules the transepithelial voltage (VT) and resistance (RT) averaged 17.2 +/- 1.4 mV, lumen positive, and 58.6 +/- 5.3 k omega X cm, respectively. The basolateral membrane voltage, (Vbl) was -29.2 +/- 2.1 mV (n = 23). The apical cell membrane did not contain appreciable ion conductances, as evidenced by the high values of apical cell membrane fractional resistance (fRa = Ra/Ra + Rb), which approached unity (0.99 +/- 0.01; n = 23). Moreover, addition of amiloride or BaCl2 to the tubule lumen was without effect on the electrical characteristics of the cell, as was a twofold reduction in luminal [Cl-]. The conductive properties of the basolateral cell membrane were assessed with bath ion substitutions. A twofold reduction in bath [Cl-] depolarized Vbl by 14.7 +/- 0.4 mV (theoretical, 17 mV), while a 10-fold increase in bath [K+] resulted in only a 0.9 +/- 0.4 mV depolarization (theoretical, 61 mV). Substituting bath Na+ with tetramethylammonium (from 150 to 75 mM) was without effect. Reducing bath [HCO-3] from 25 to 5 mM (constant PCO2) resulted in a steady-state depolarization of Vbl of 8.4 +/- 0.4 mV that could not be attributed to conductive HCO-3 movement. Thus, the basolateral cell membrane is predominantly Cl- selective.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological identification of principal and intercalated cells in the rabbit outer medullary collecting duct.

Intracellular microelectrode techniques were used together with inhibitors of Na+ transport (amiloride) and H+ transport (acetazolamide and SITS) to identify principal cells and intercalated cells in the outer stripe of the rabbit outer medullary collecting duct. The principal cell (n = 9) had a basolateral membrane voltage (Vbl) of -64.7 +/- 3.2 mV, a fractional resistance of the apical membrane (fRa = Ra/Ra + Rbl) of 0.82 +/- 0.02, and a K+-selective basolateral membrane. Luminal amiloride hyperpolarized Vbl by 10.3 +/- 2.1 mV and increased fRa to near unity (n = 7). Bath acetazolamide and SITS were without effect on these parameters. The intercalated cell (n = 5) had a Vbl of -25.0 +/- 3.2 mV, a fRa of 0.99 +/- 0.01, and a Cl(-)-selective basolateral membrane. Bath acetazolamide or SITS hyperpolarized Vbl by 26.4 +/- 8.2 mV. Luminal amiloride did not alter Vbl of this cell. The differential effects of the inhibitors also indicate that the principal and intercalated cells are probably not directly coupled electrically.

Conductive properties of the rabbit outer medullary collecting duct: outer stripe.

Segments of the outer medullary collecting duct were dissected from the outer stripe of the rabbit kidney (OMCDo) and perfused in vitro. The conductive properties of the tubule epithelium and individual cell membranes were determined by means of cable analysis and intracellular voltage-recording microelectrodes. The transepithelial voltage (VT) and resistance (RT) averaged -10.7 +/- 2.5 mV, lumen negative, and 28.5 +/- 2.9 k omega X cm (n = 27), respectively. Two cell types could be defined by their electrophysiological properties. One cell type (n = 7) had a mean basolateral membrane voltage (Vbl) of -30.1 +/- 2.4 mV, a fractional resistance of the apical membrane (fRa = Ra/Ra + Rbl) near unity (0.99 +/- 0.01), and a predominantly Cl(-)-selective basolateral cell membrane. The second cell type (n = 27) had a mean Vbl of -63.7 +/- 2.7 mV, a fRa of 0.81 +/- 0.02, and a predominantly K+-selective basolateral cell membrane. The present study focused on defining the conductive properties of this latter cell type. Amiloride (10(-5) M) and BaCl2 (2 mM) were used as probes of apical cell membrane Na+ and K+ conductive pathways, respectively. Amiloride increased fRa from 0.80 +/- 0.02 to 0.98 +/- 0.01 (n = 12), whereas BaCl2 increased fRa from 0.77 +/- 0.03 to 0.82 +/- 0.03 (n = 9). The conductive properties of the basolateral cell membrane were assessed by ion substitutions of the bath solution. A 10-fold increase in the bath [K+] depolarized Vbl by 34.9 +/- 1.9 mV (n = 16) in less than 1 s, indicating that this membrane was predominantly K+ selective.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology of collecting duct H+ secretion: effect of inhibitors.

Segments of the outer medullary collecting duct were isolated from the inner stripe of the rabbit kidney (OMCDi), perfused in vitro, and impaled across their basolateral membranes with voltage-recording microelectrodes. The disulfonic stilbene 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (10(-4) M) and the carbonic anhydrase inhibitor acetazolamide (10(-4) M) depolarized the lumen-positive transepithelial voltage (VT) toward 0 mV when added to the bath solution. Concurrently, the basolateral membrane voltage (Vbl) hyperpolarized. The hyperpolarization of Vbl, which averaged 19.3 +/- 2.9 mV (n = 11) for SITS and 22.7 +/- 3.5 mV (n = 11) for acetazolamide, was not due to an alteration in the ionic selectivity of the basolateral membrane, which was highly Cl- selective. The hyperpolarization of Vbl could best be explained by a decrease in the intracellular [Cl-], and the associated shift in the emf for Cl- (ECl) across the basolateral membrane. The decrease in intracellular [Cl-] could be attributed to inhibition of a Cl-HCO3 antiporter in the basolateral membrane. SITS appeared to inhibit this antiporter directly, whereas the effect of acetazolamide was indirect, probably secondary to a decrease in the intracellular [HCO3-]. Finally, both SITS and acetazolamide induced or unmasked an electroneutral K+-coupled transport system in the basolateral membrane.

Electrophysiological properties of cultured outer medullary collecting duct cells.

Whole cell patch-clamp techniques were used to characterize the electrophysiological properties of cells from the inner stripe portion of the rabbit outer medullary collecting duct (OMCDi) grown in primary culture. With pipette and bathing solutions mimicking intracellular and extracellular fluid, the resting membrane voltage was -30 to -40 mV. The whole cell conductance exhibited slight outward rectification, and at the resting membrane voltage the cell conductance averaged 2.58 +/- 0.49 nS (n = 17). The major conductive ion species was Cl-. The Cl- conductance was also found to have a significant permeability to HCO3- and was inhibited by the Cl(-)-channel blockers diphenylamine carboxylic acid and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. A small K+ conductance was also present, but no Na+ conductance was detected. Current generated by the H(+)-adenosinetriphosphatase (H(+)-ATPase) was quantitated. This current was dependent on the presence of ATP in the pipette. Dicyclohexylcarbodiimide, N-ethylmaleimide, and bafilomycin A1, inhibitors of the vacuolar H(+)-ATPase, also reduced this outward current in an ATP-dependent manner. The inhibitor-sensitive component of the outward current, a measure of the current generated by the H(+)-ATPase, was in the range of 35-100 pA/cell.

Characterization of acid-base transporters in cultured outer medullary collecting duct cells.

Cells from the inner stripe of the rabbit outer medullary collecting duct (OMCDi) were grown in primary culture, and their acid-base transport properties were characterized using intracellular pH (pHi) measurements with the fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Basal pHi in HCO(3-)-buffered solutions was 7.28 +/- 0.04 (n = 20). The presence of a Cl-/HCO(3-)-antiporter was demonstrated by reversible alkalinization on bath Cl- removal. The mean alkalinization seen on Cl- removal was 0.16 +/- 0.02 pH units (n = 20) and was inhibited 92% by 10(-4) M 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Studies were also performed to determine the presence of an Na+/H+ antiporter and an H(+)-adenosinetriphosphatase (H(+)-ATPase). After an NH4Cl acid load the cells exhibited both Na(+)-dependent and Na(+)-independent pHi recovery mechanisms. The Na(+)-dependent mechanism was inhibited by amiloride. The Na(+)-independent mechanism was completely inhibited by 10(-3) M N-ethylmaleimide or 2.5 x 10(-9) M bafilomycin A1, but was not significantly altered by removal of bathing solution K+. Thus, the Na(+)-dependent recovery mechanism exhibited characteristics of an Na+/H+ antiporter, whereas the Na(+)-independent recovery mechanism was consistent with the presence of an H(+)-ATPase.

Mineralocorticoid regulation of sodium and potassium transport by the cortical collecting duct.

Chronic high-dose mineralocorticoid hormone treatment of rabbits results in marked alterations of the structure and function of the cortical collecting duct. Most importantly, the reabsorption of Na+ and the secretion of K+ are increased. Intracellular microelectrode measurements provide evidence consistent with the idea that the increased transport of these ions is a result of changes in the membrane conductances and electrochemical driving forces for passive ion movement and of the activity of the Na+,K+-ATPase. Specifically, the Na+ and K+ conductances of the apical membrane are increased, and the cellular potential profile is altered to promote transcellular movement of K+ from the peritubular to the luminal fluid compartments. The associated increase in the activity of the Na+,K+-ATPase facilitates extrusion of Na+ from and accumulation of K+ into the cell. The resistance of both the apical and basolateral cell membranes are reduced with DOCA treatment, while the resistance of the paracellular pathway is increased. Consequently, the electrophysiological properties of the tubule epithelium reflect to a greater degree the properties of the transcellular pathway.

Acidification of luminal fluid by the rabbit cortical collecting tubule perfused in vitro.

The ability of the rabbit cortical collecting tubule to acidify the luminal fluid was determined with double-barreled antimony pH electrodes. In Na+/K+ Ringer the tubules maintained a transepithelial voltage (VToc) of -45.4 +/- 5.5 mV (bath grounded) and a minimum luminal fluid pH of 5.93 +/- 0.11. Chronic mineralocorticoid pretreatment of the rabbits caused the VToc to become more negative (-78.7 +/- 8.2 mV) and decreased the minimum luminal fluid pH to 5.43 +/- 0.16. In most tubules (control and mineralocorticoid-pretreated) the measured pH was more acidic than could be accounted for by either the lumen-negative VToc or CO2 equilibration of the perfusion fluid. When tubules were perfused and bathed in 0 Na+/0 K+ Ringer they developed a lumen-positive VToc, which was stimulated by mineralocorticoid, was sensitive to the PCO2 of the bathing solutions, but was not dependent on Cl- in either the luminal or bath solutions. Luminal acidification in the absence of Na+ and K+ (pH = 6.05 +/- 0.12) occurred against a lumen-positive VToc of +11.5 +/- 1.9 mV. Addition of 10(-4) M ouabain to the bath of tubules studied in Na+/K+ Ringer caused the VToc to reverse polarity and the luminal fluid pH to increase. In contrast, ouabain had no effect on either the lumen-positive VToc or the minimum luminal fluid pH when added to the bath of tubules in 0 Na+/0 K+ Ringer. Bath addition of 10(-4) M acetazolamide and/or 5 X 10(-4) M 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) caused alkalinization of the luminal fluid in tubules studied in either Na+/K+ or 0 Na+/0 K+ Ringer. In 0 Na+/0 K+ Ringer, acetazolamide and SITS reduced the lumen-positive VToc to near zero. The data support the existence of a distinct acidification mechanism in the rabbit cortical collecting tubule, which is both active and electrogenic.

Effect of general anaesthesia on renal haemodynamics in the rat.

1. The effect of sodium pentobarbital and Inactin anaesthesia on renal haemodynamics in the rat was evaluated with radioactive microspheres 15 micrometer in diameter. 2. Both anaesthetic agents caused substantial decrements in total renal blood flow (sodium pentobarbital, -34%; Inactin, -24%) compared with unanaesthetized animals. 3. Measurements of renal function obtained in rats anaesthetized with either of these anaesthetic agents should be interpreted with caution.

Beta-adrenergic regulation of H+ secretion by cultured outer medullary collecting duct cells.

The effects of the beta-adrenergic agonist isoproterenol (Iso) on cells of the inner stripe portion of the rabbit outer medullary collecting duct (OMCDi) grown in primary culture were examined using whole cell patch-clamp techniques and measurements of intracellular pH (pHi) and Ca2+. Iso (10(-6) M) increased the cellular Cl- conductance, and this effect was mimicked by treatment of the cells with dibutyryladenosine 3',5'-cyclic monophosphate (cAMP, 10(-5) M) or protein kinase A (PKA, 0.4 U/ml). Iso did not alter the baseline pHi, but it did increase the activity of both the Cl-/HCO3- antiporter and the H(+)-adenosinetriphosphatase (H(+)-ATPase). The increase in Cl-/HCO3- antiporter rate was mimicked by dibutyryl-cAMP plus 3-isobutyl-1-methylxanthine (cAMP + IBMX, 10(-4) M + 10(-5) M). However, the Iso-induced stimulation of the H(+)-ATPase activity was not mimicked by cAMP + IBMX. Measurements of intracellular Ca2+ showed that Iso also increased intracellular Ca2+ levels. This response was not dependent on extracellular Ca2+, nor did cAMP + IBMX appreciably alter intracellular Ca2+. Consequently, we postulate that beta-adrenergic agonists are potential stimulators of OMCDi H+ secretion. These agonists stimulate cellular HCO3- efflux through a signal transduction pathway involving cAMP and PKA. However, a different signal transduction pathway appears to mediate the stimulation of cellular H+ efflux. This second pathway may involve an elevation of intracellular Ca2+.

Intracellular microelectrode characterization of the rabbit cortical collecting duct.

Cortical collecting ducts of the rabbit were perfused in vitro and the intracellular potential (Vbl) was measured with KCl-filled microelectrodes. The ratio of apical to basolateral membrane resistance (Ra/Rbl) was estimated from the voltage divider ratio using cable analysis. In control tubules Vbl averaged--84.0 +/- 2.5 mV and Ra/Rbl was 0.83 +/- 0.11. Pretreatment of the rabbits with mineralocorticoid caused Vbl to hyperpolarize to--105.8 +/- 3.1 mV and Ra/Rbl to decrease slightly to 0.62 +/- 0.10. A 10-fold increase of the luminal [K+] caused a 40.6 +/- 3.1 mV depolarization of Vbl in control tubules and a 33.0 +/- 4.2 mV depolarization in tubules from DOCA-pretreated rabbits. Concurrently, Ra/Rbl decreased in both groups, consistent with the existence of a conductive K+ channel at the apical cell membrane. This apical K+ channel was not sensitive to amiloride but was blocked by Ba2+. Conductive movement of Na+ across the apical membrane was also apparent in that Ra/Rbl increased with amiloride from 0.61 +/- 0.10 to 1.45 +/- 0.28. A 10-fold increase in the bath [K+] caused a 28.6 +/- 3.8 and a 49.4 +/- 4.4 mV depolarization of Vbl in tubules obtained from control and DOCA-pretreated rabbits, respectively. In both groups Ra/Rbl increased, suggesting that the basolateral cell membrane also contains a conductive K+ channel. Taken together the results support a model in which the transepithelial reabsorption of Na+ and the transepithelial secretion of K+ are driven by the Na+-K+-ATPase located in the basolateral cell membrane, with passive movement of these ions occurring through separate conductive pathways in the apical cell membrane.

Single-channel currents in renal tubules.

Patch-clamp techniques were used to study isolated renal cortical collecting ducts of rabbits. Gigaohm seals of the native apical membranes of the principal cells were obtained from tissues superfused with a Ringer solution. No enzymatic or other pretreatment of the tissues was required. The patches studied were primarily of the on-cell type, although excised patches could be obtained. Unitary currents in a range of tenths of picoamperes were observed at holding voltages between +/- 100 mV. Since the apparent reversal potential was at a holding voltage at or near 0 eatment of the tissues was required. The patches studied were primarily of the on-cell type, although excised patches could be obtained. Unitary currents in a range of tenths of picoamperes were observed at holding voltages between +/- 100 mV. Since the apparent reversal potential was at a holding voltage at or near 0 eatment of the tissues was required. The patches studied were primarily of the on-cell type, although excised patches could be obtained. Unitary currents in a range of tenths of picoamperes were observed at holding voltages between +/- 100 mV. Since the apparent reversal potential was at a holding voltage at or near 0 mV and since the current-voltage relationship was markedly nonlinear, the unitary currents are most likely due to K+ . Na+-channel current fluctuations, if present, could not be uniquely identified in the presence or absence of amiloride.

Electrical characteristics of snake distal tubules: studies of I-V relationships.

Distal tubules of Thamnophis spp. were perfused in vitro with Ringer solution containing either 16 or 150 mM Na and bathed with 150 mM Na Ringer. Current-voltage relationships were obtained by injecting pulses of constant current, Io, into the tubule lumen and recording changes in voltage, delta Vo, at the proximal end of the perfused tubule segment. The Io-Vo plots showed a distinct break at a voltage E1 (approximately 85 mV) that was greater than the open-circuit voltage, VToc, and similar to values of ENa, the transepithelial driving force for Na transport estimated by other methods. The resistance of the shunt pathway, Rs, was estimated from the values of the transepithelial resistance after luminal addition of 10(-5) M amiloride, which caused a rapid fall of the VToc to 0 mV with concurrent increases of the transepithelial resistance. These estimates of Rs were the same as the values of E1/I1 obtained from the Io-Vo plots. The VToc, RT, and Rs were independent of the bath [Na] and were not influenced by the addition of amiloride to the bath. As in frog skin and toad urinary bladder, the ENa and Rs of the snake distal tubule can be estimated from studies of their Io-Vo plots, and the E1 appears to be independent of the transepithelial chemical potential for Na.

Luminal Na concentration and the electrical properties of the snake distal tubule.

In previous studies of isolated perfused distal tubules of Thamnophis spp., elevation of luminal [Na] from 16 to 150 mM resulted in a transient hyperpolarization of the open-circuit voltage, VToc. To characterize further this response, studies were done to examine the concurrent changes of the transepithelial resistance, RT. After elevation of luminal [Na] from 16 to 150 mM. the VToc increased sharply from a mean of 38.5 to 61.2 mV and the RT decreased from a mean of 22.3 to 15.8 k omega x cm. Thereafter, the VToc declined slowly below control values, and the RT increased well above control values. The short-circuit current calculated as VToc/RT changed in parallel with the VToc, increasing at first (from 1.8 to 4.1 microA/cm) and then falling to about 0.2 microA/cm. Luminal addition of 10(-5) M amiloride caused th VToc leads to 0 and the RT to increase during control and all phases of the transient. On the assumption that RT during amiloride perfusion is the same as the shunt resistance, Rs, the values of the transepithelial driving force, ENa, and its series resistance, RNa, were calculated. An analysis of the data in this way indicated that the principal changes in the epithelium could be attributed to alterations of the RNa and not the ENa or Rs.

Patch clamp studies of apical membranes of renal cortical collecting ducts.

Patch clamp techniques were used in study of the apical membrane of isolated renal cortical collecting ducts. Whereas on-the-cell patches (reported previously) gave channel activity due primarily to K+, isolated inside-out patches of the same membranes bathed with 150 mM Na+, 5 mM K+, and 1 mM Ca2+ gave channel activity due primarily to Na+. Na+ channels could remain either open or closed for periods of milliseconds to minutes. Although unitary currents of tenths of a pA were observed routinely, patch activity could change spontaneously between quiescent and violent with 'apparent' unitary currents of several pA. It was not possible to rule out the idea that the complex activity of the patches was due to synchronous or near synchronous openings/closings of several channels of identical unitary current. The unpredictable spontaneous changes of patch activity make difficult the design of experiments to test for the influence of agents expected or suspected to alter channel behavior.