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Biomedical subjects

E E Windhager

Publications and source records attributed to E E Windhager.

At least 37 records · Page 2Linked to original sources
PubMed1984

Cytosolic Ca2+ and Na+ activities in perfused proximal tubules of Necturus kidney.

To study the role of intracellular calcium in the regulation of epithelial transport of ions and water, cytosolic calcium ion activity (aiCa) and cytosolic sodium ion activity (aiNa) were measured in cells of isolated perfused proximal tubules of Necturus kidney. aiCa was measured with Ca2+-selective microelectrodes, aiNa with Na+-selective microelectrodes. Under control conditions, i.e., Ringer solution on both sides of the epithelium, aiCa averaged 71 +/- 7 (SE) nM (n = 21) and aiNa was 12.9 +/- 0.6 mmol (n = 56). When peritubular bath sodium was reduced from 100 to 10 mM by choline substitution, aiCa increased from 73 +/- 14 to 382 +/- 69 nmol (paired t test; P less than 0.001; n = 4); in different tubules, aiNa decreased from 12.8 +/- 1.9 to 8.2 +/- 1.8 mM (P less than 0.001; n = 12). Quinidine (10(-4) M) increased aiCa from 87 +/- 19 to 556 +/- 121 nM (P less than 0.02; n = 5) but reduced aiNa from 15.1 +/- 1.2 to 11.8 +/- 0.8 mM (P less than 0.003; n = 8). In contrast, 10(-4) M ouabain increased both aiCa and aiNa; aiCa rose from 71 +/- 9 to 546 +/- 121 nmol (P less than 0.005; n = 9) and aiNa from 15.1 +/- 1.8 to 70.1 +/- 6.3 mM (P less than 0.001; n = 9). The results are consistent with the existence of a Na-Ca exchange process within the contraluminal cell membrane and with the view that increased aiCa inhibits the tubular transport of sodium by decreasing the sodium permeability of the luminal cell membrane.

Animals↗
PubMed1983

pH effect on osmotic response of collecting tubules to vasopressin and 8-CPT-cAMP.

The effect of peritubular and luminal pH changes on hydraulic conductance, (Lp, 10(-7) cm X s-1 X atm-1) in the isolated perfused rabbit cortical collecting tubule (CCT) was tested at 37 degrees C before and after administration of 20 microU/ml vasopressin or 10(-4) M 8-[p-chlorophenylthio]-adenosine cyclic monophosphate (8-CPT-cAMP). In vasopressin experiments when bath pH was changed from 7.58 to 7.16 or from 7.58 to 6.70, mean Lp decreased from 249 +/- 32 to 199 +/- 23 (n = 5; P less than 0.01) and from 231 +/- 38 to 201 +/- 36 (n = 5; NS), respectively. In contrast, in 8-CPT-cAMP experiments when bath [HCO3] was kept constant while CO2 was elevated the hydroosmotic response was increased. Using 2.5 mM HCO3, Lp at 0.4% CO2 was 275 +/- 15 and at 6% CO2 it was 352 +/- 50 (n = 4; paired t test; P less than 0.05). At 8.5 and 21.5 mM HCO3 raising CO2 from 2 to 13% and from 4 to 32% increased Lp from 237 +/- 71 to 410 +/- 32 (n = 4; paired t test; P less than 0.05) and from 282 +/- 45 to 449 +/- 63 (n = 6; paired t test; P less than 0.001), respectively. Reducing luminal pH from 7.40 to 5.40 had no effect on either vasopressin- or cAMP-induced changes in Lp. Accordingly, lowering the bath pH by increasing the PCO2 at constant [HCO3] markedly stimulates the response to 8-CPT-cAMP, whereas lowering the bath pH by reducing [HCO3] inhibits the vasopressin response.

Animals↗
PubMed1982

Cellular and paracellular resistances of the Necturus proximal tubule.

Individual resistances of the apical cell membrane Ra, the basolateral cell membrane, Rbl, and the paracellular shunt, Rs, were determined in the Necturus proximal tubule using a set of three electrical parameters. Four electrical parameters were measured: the transepithelial resistance, (Rte), the apical and basolateral cell membrane resistance in parallel, (Rz free-flow tubules), the basolateral cell membrane resistance in oil-filled tubules, (Rz oil-filled), and the ratio of apical and basolateral cell membrane resistance (Ra/Rbl). Rte was determined from an analysis of the spatial decay of luminal voltage following luminal current injection. Rz free-flow and Rz oil-filled were measured by the analysis of the spatial decay of intracellular voltage deflections following cellular current injection in free flow and oil-filled tubules, respectively. Ra/Rbl was estimated from the ratio of voltage deflections across the apical and basolateral cell membranes following transepithelial current injection. In addition, the magnitude of cellular and luminal cable interactions was evaluated, by comparing the spatial decay of voltage deflections in the cell and in the lumen following intracellular current injection. The combined cell membrane resistance (Ra + Rbl) is between one to two orders of magnitude greater than the paracellular resistance. This result supports the view that the Necturus proximal tubule is a leaky epithelium.

Animals↗
PubMed1982

Hydroosmotic response of collecting tubules to ADH or cAMP at reduced peritubular sodium.

Changes in cytosolic Ca2+ activity have been implicated in the hydroosmotic response to vasopressin (VP) in amphibian urinary bladder; the level of cytosolic free Ca2+ may be regulated, in part, by a process of Na-Ca exchange across the basolateral cell membrane. To assess whether similar mechanisms operate in the mammalian nephron, the effect of low peritubular [NA] on the hydraulic conductivity (Lp) of the isolated perfused rabbit collecting tubule (CT) exposed to either 20 microunits/ml VP or 5 X 10(-5) M 8-[p-chlorophenylthio]-cyclic 3',5'-adenosine monophosphate (ClPheS-cAMP) was studied. Low peritubular [Na] had no effect on the basal water permeability of the CT. After exposure to VP, CTs bathed in 145 mM Na Ringer solution developed an Lp of 324 +/- 27 X 10(-7) cm.s-1.atm-1, while tubules bathed in 4 mM Na and 141 mM tetramethylammonium Ringer solution achieved an Lp of only 112 +/- 13 X 10(-7) cm.s-1.atm-1 (P less than 0.001). Inhibition of the VP response was estimated to be half-maximal when peritubular Na was 120 mM. The hydroosmotic response to ClPheS-cAMP was diminished by 44% of the control values when CTs were bathed in a 4 mM Na medium; this inhibition was greatly attenuated when the peritubular Ca concentration was reduced to 0.05 mM. These results are consistent with the view that 1) a Na-Ca exchange process operates at the basolateral surface of the mammalian cortical collecting tubule cells, and 2) elevated cytosolic Ca ion activity inhibits the increase in water permeability elicited by VP or cAMP in this nephron segment.

Animals↗
PubMed1981

Sodium-calcium interactions in the renal proximal convoluted tubule of the rabbit.

The effect of experimental maneuvers believed to raise cytosolic [Ca2+] on Na and fluid absorption by isolated perfused proximal convoluted tubules of rabbit kidneys was examined. For this purpose experiments were carried out in which either 1) peritubular [Na] was lowered from 145 mM in controls to 40 mM in experimental periods by isosmotic replacement with Li, tetraethylammonium, or choline; or 2) quinidine (10(-4) M) or A 23187 (5 X 10(-6) M) was added to the peritubular bath containing 145 mM Na. Fluid absorption (Jv), transepithelial unidirectional Na efflux (JNa 1 leads to b), and Na influx (JNa b leads to 1) were measured. Lowering peritubular [Na] inhibited JNa 1 leads to b by 28% and Jv by 61% of the control values. The degree of inhibition of Jv by low peritubular [Na] was dependent on the concentration of ultrafilterable calcium ([Ca]UF) over the range of 0.2-1.0 mM: as perfusate and bath ultrafilterable calcium was reduced, there was an attenuation of the low [Na]-induced inhibition of Jv. Above 1.0 mM [Ca]UF no further increase in inhibition of Jv was observed. Quinidine in the bath inhibited Jv by 37% and JNa 1 leads to b by 28%; A 23187 reduced Jv by 37% and JNa 1 leads to b by 15%. These results are consistent with the view that cytosolic [Ca2+], in turn dependent on a Na-Ca exchange mechanism located at the basolateral cell membrane, regulates, in part, the rate of proximal tubular efflux of sodium, calcium, and water.

Animals↗
PubMed1980

Effects of PTH, ADH, and cyclic AMP on distal tubular Ca and Na reabsorption.

Tubular microperfusion experiments were performed in rats to examine the effects of thyroparathyroidectomy (TPTX), parathyroid hormone (PTH), antidiuretic hormone (ADH), and cyclic AMP (cAMP) on distal tubular Ca, Na, and water reabsorption. TPTX caused a significant decrease in the Ca reabsorptive rate as compared to intact animals. PTH (5 U/kg; 2 U x kg-1 x h-1) replacement in TPTX animals restored Ca transport to control levels. Application of either cAMP (10(-3) M) or 8-(p-chlorophenylthio)-cyclic 3',5'-adenosine monophosphate (10(-5) M) to the surface of the kidney caused a stimulation of Ca reabsorption similar to that produced by PTH. Neither TPTX nor PTH changed Na or water reabsorption significantly, whereas the cyclic nucleotides increased both of these parameters. These later actions of cAMP duplicated effects of ADH observed in these distal tubules.

Animals↗
PubMed1979

Possible role of cytosolic calcium and Na-Ca exchange in regulation of transepithelial sodium transport.

Emerging evidence in a number of different epithelia suggests that changes in cytosolic calcium ion levels play a critical role in the regulation of transepithelial sodium transport. Maneuvers believed to raise cytosolic calcium ion activity lead to an inhibition of net sodium transport in toad urinary bladder, frog skin, and isolated perfused proximal renal tubules. Regulation of the level of ionized calcium in the cytosol of the epithelial cells appears to involve a process of coupled Na-Ca exchange across the basolateral plasma membrane, energized, at least in part, by the sodium gradient. It is suggested that changes in cytosolic calcium ion levels, secondary to changes in Na-Ca exchange, in turn dependent in part on the activity of the sodium pump, constitute a link in a negative feedback mechanism. Through such a feedback mechanism, the rate of entry of sodium into the cell across the apical surface may be kept in step with its rate of extrusion across the basolateral surface.

Animals↗
PubMed1978

Calcium and sodium transport by the distal convoluted tubule of the rat.

Calcium and sodium transport were studied in the distal convoluted tubule of the rat by micropuncture and microperfusion techniques. The animals received either control infusions, 0.9% saline at 0.02 ml/min, or chlorothiazide (CTZ), 0.5 mg/min-kg. In free-flow micropuncture, distal calcium reabsorption occurred against an electrochemical gradient; it was 9% of the filtered load in the controls and 13.8% in the CTZ-treated rats. The drug dissociated calcium and sodium transport along the distal tubule. Absolute reabsorptive rates for calcium and sodium, measured in pump perfusion experiments, were proportional to the distal loads. CTZ, acting from the lumen, enhanced net calcium (P less than 0.01) and reduced net sodium (P less than 0.01) reabsorption. In stationary microperfusion experiments, sodium backflux produced rapid establishment of a steady-state concentration of 50 mM. In contrast, net backflux of calcium was negligible. With calcium in the luminal perfusion fluid, there was a concentration-dependent reabsorptive efflux which was not saturated at a luminal calcium concentration of 9.5 mM and which was enhanced by CTZ.

Animals↗
PubMed1975

Estimate of relative thickness of peritubular interstitial space in Necturus kidney.

Electrophysiological techniques were used to evaluate volume changes of compartments interposed between the peritubular membrane of proximal tubue cells and capillary wall or peritoneal surface of Necturus kidney. The time courseof potassium-induced peritubular membrane depolarization was measured during a switch from 3- to 90-meq potassium sulfate solution in superfusion as well as in vascular perfusion experiments. When superfusion fluids contained 6, 2, and 0 g dextran/100 ml, mean half times of depolarization in normal kidneys were 4.1, 1.9, and 5.8 s. Decreasing the colloid osmotic pressure of superfusion fluids resulted in a significant increase in half-time values. Similar results were obtained in saline expansion. In controls the mean half time was 4.5s; in saline expansion it was 7.7 s. In vascular perfusions, mean half-time values were 225, 350, 355, and 450 s for dextran concentrations of 6, 4, 2, and 0 g/100 ml, respectively. These results indicate that the half time of depolarization increases significantly as the colloid osmotic pressure of perfusion fluids decreases. Estimates of effective unstirred-layer thickness on the peritubular side of proximal tubular epithelium indicate a decrease by about 25% when vascular colloid osmotic pressure is increased from 0 to 54 mmHg.

Animals↗
PubMed1975

Osmotically induced changes in electrical resistance of distal tubules of rat kidney.

Changes in peritubular oncotic pressure do not alter the electrical resistance of distal convoluted tubules. Transverse specific electrical resistance decreases along the distal convoluted tubule in nondiuretic rats. This drop in resistance can be at least in part accounted for by the relative increae in osmolality of late distal fluid. Osmotic gradients influence the magnitude of intercellular rather than transcellular conductance. Hyposmolality of tubular fluid leads to reduced shunting, whereas increased tubular osmolality has the opposite effect. The osmotic effect forms part of an intraepithelial positive feedback loop for sodium reabsorption in the diluting segment of the renal nephron.

Animals↗