Characteristics of Naplus-Kplus-stimulated ATPase in rabbit gall bladder epithelium

Influence of serosal hydrostatic pressure on net water and electrolyte transport across the isolated rat colonic mucosa exposed to different secretagogues

The influence of 2 cm and 7 cm hydrostatic pressure applied upon the serosal side on net water and electrolyte transport and paracellular permeability was investigated in everted sacs of stripped rat colon mucosa exposed to different secretagogues. A 2 cm pressure abolished net fluid absorption in the presence of deoxycholic acid, bisacodyl, ethacrynic acid and rhein and reduced absorption in the tissue pretreated with cholera toxin. The paracellular permeability was increased by deoxycholic acid, bisacodyl and ethacrynic acid and diminished under the influence of rhein and cholera toxin. At a pressure of 7 cm H2O fluid movement was directed toward the mucosal side parallel to the increase of the paracellular permeability. The fluid appearing at the mucosal side was isotonic in the presence of deoxycholic acid, ethacrynic acid and rhein but hypotonic when the tissue was pretreated with cholera toxin. From the pressure-induced net water flow and the composition of the transferred fluid secretagogues acting predominantly on paracellular pathway can be distinguished from secretagogues acting on basis of other mechanisms.

Effect of temperature on the pH dependence of renal microsomal ATPase in the rabbit, rat and hamster

The effects of temperature on the optimum pH of the renal microsomal Na-K-ATPase were studied in the rabbit, rat and hamster. The pH optimum of the ATPase in all three animals varied inversely with temperature, while a constant optimal OH-/H+ ratios were preserved at all temperatures. There appeared to be no difference between the Na-K-ATPase of the hibernating and non-hibernating representatives in terms of temperature dependence or substrate affinity. The pH optimum for the K-pNPPase activity was independent of temperature, indicating that the dephosphorylation step of Na-K-ATPase catalyzed reactions is not the source of the temperature dependence. These results are consistent with the Imidazole alphastat hypothesis of Reeves, which predicts that the optimal activity of the enzyme would occur at a constant pH-pKIM and thus a constant OH-/H+ ratio.

Ouabain and regulation of cellular volume in slices of mammalian renal cortex

1. The effect of ouabain on cellular volume recovery in rabbit, guinea-pig and rat renal cortical slices was studied. A concentration of ouabain that is maximally effective in inhibiting slice potassium accumulation was determined for each species. Slices from each species were either freshly prepared and then incubated, or leached and then incubated, or preincubated in oxygenated ordinary medium (equilibrated), leached and then reincubated in media with and without this concentration of ouabain. All incubations were at 25 degrees C.2. Potassium loss produced by ouabain was greater in rabbit and guinea-pig slices than in rat slices.3. With slices that were freshly prepared and then incubated, and with slices that were leached and then incubated, cellular volume recovery was inhibited by ouabain in rabbit and guinea-pig slices, but not in rat slices.4. After equilibration, swelling during leaching was less, especially in rabbit and guinea-pig slices. However, on subsequent reincubation, significant differences in tissue water and cation contents that were consistent with inhibition of cellular volume recovery by ouabain, were seen in slices from these two species, but not in rat slices.5. Slices from all three species, when incubated with concentrations of ouabain that were maximally effective in inhibiting potassium accumulation, appeared to approach a steady-state tissue potassium content that was greatest in rat slices and least in rabbit slices. Rat slices, previously depleted of potassium, reaccumulated potassium in the presence of 10 mm-ouabain to reach this steady-state potassium content.6. Despite superficial appearance to the contrary (especially in the case of rat slices) these results are consistent with a major role for the conventional pump in controlling cortical cell volume. They do not provide evidence for the postulate that renal cortical cells possess a separate, ouabain-insensitive mechanism regulating cell volume.

Effects of ethacrynic acid on electrolyte and fluid transport by the guinea pig gallbladder

The effect of ethacrynic acid on fluid and electrolyte transport by the guinea pig gallbladder was investigated in vitro. 10-4M ethacrynic acid, applied to the serosal side, inhibited fluid and sodium chloride absorption. The reduction in salt absorption was accounted for by a 3 muEq/cm2h decrease in the unidirectional fluxes of Na and Cl from mucosa to serosa with no change in the fluxes from serosa to mucosa. Ethacrynic acid (10-4 M) had no effect on HCO3 - Cl exchange, PGE1-induced fluid secretion and inulin permeability. At 10-3 M, ethacrynic acid markedly increased both the serosa to mucosa fluxes of Na and Cl, and the inulin permeability. Examination by light and electron microscopy of gallbladder tissue treated with 10-3 M ethacrynic acid revealed large intracellular vacuoles and occasionally ruptured apical cell membranes. Only slight morphological changes were seen by 10-4 M ethacrynic acid with no changes in the controls and ouabain treated gallbladders. The effects of ethacrynic acid are remarkably different from those of furosemide which has been previously shown to inhibit only the HCO3 secretion leaving fluid and NaCl absorption unchanged.

Functional distinction between two transport mechanisms in rabbit gall-bladder epithelium by use of ouabain, ethacrynic acid and metabolic inhibitors

1. Net fluid transport rate, transepithelial p.d. and resistance, and unidirectional Na+-fluxes were measured in rabbit gall-bladder preparations exposed on both sides to bicarbonate-Ringer solution in vitro. 2. Both ouabain and ethacrynic acid (ETCA) caused dose-dependent decreases of net fluid transport rate; ouabain inhibited fluid transport predominantly from the serosal side, whereas the inhibitory effect of ETCA was elicited mainly from the mucosal (luminal) side. Applied bilaterally, the ID50 for ouabain was 2.5 X 10(-6) M, and for ETCA 2.3 X 10(-4) M. After maximal inhibition at each concentration level of the two inhibitors fluid transport could not be reversed. 3. 2,4-Dinitrophenol (2,4-DNP) (2 X 10(-4) M) or substitution of O2 by N2 caused an 80% reversible decrease of net fluid transport. 4. The spontaneous p.d. across the rabbit gall-bladder was about 2.7 mV, mucosal side positive. 2,4-DNP, N2 and serosal application of ouabain depressed the p.d. after an initial hyperpolarization. This decrease was reversible during recovery from 2,4-DNP and N2, but irreversible after removal of ouabain at concentrations greater than or equal to 10(-4) M. Mucosal application of ETCA (10(-3) M) caused no decrease in p.d., which actually increased slightly. 5. Calculated passive serosal-to-mucosal Na+-fluxes changed in the same direction as did changes in conductance. 6. It is concluded that ETCA does not interfere primarily with the Na-K-ATPase or cellular oxidative metabolism. The data support the proposal that the pump responsible for isosmotic transepithelial fluid transfer is located in the luminal end of the cells. This pump is ETCA-sensitive. The ATPase-dependent Na-K pump, which can be inhibited by ouabain, is localized in the serosa-facing cell membrane. The data suggest that the inhibition of net fluid transport by ouabain is indirect and mediated by changes in intracellular ion concentrations. 7. The results support the concept that the transepithelial fluid transport mechanism is electroneutral, and suggest that the mucosa positive transepithelial p.d. is due to differences in electromotive forces arising from ion (mainly K+) diffusion across the mucosal and serosal cell membranes.

Quantitative evaluation of retrograde arterial flow in chronic experimental arteriovenous fistulas

A 2 cm long iliac av. fistula is established in 13 dogs. Flow measurements are performed in the fistula limbs and the adjacent arteries immediately (stage I), as well as 3 months (stage II) and 6 to 12 months (stage III) post-shunt. The following results are obtained: 1) In the acute stage, average flow in the distal fistula artery is very small but directed towards the periphery. In stages II and III a progressively increasing retrograde flow directed towards the fistula is regularly measured in the distal fistula artery. 2) Even in the acute stage a considerable retrograde flow is measured in the distal fistula artery when the proximal artery is clamped. Likewise, in stages II and III, this "free" retrograde flow (after occlusion of proximal fistula artery) is 40 to 60% higher than the spontaneous retrograde flow. 3) In chronic av. fistulas, the "free" retrograde flow in the distal fistula artery decreases significantly after occlusion of the adjacent tail artery and the contralateral iliac artery. It can thus be calculated that in chronic iliac av. fistulas the tail artery contributes approximately 44% and the contralateral iliac artery 22% to retrograde arterial fistula flow. The remaining 34% of retrograde flow are mainly derived from collaterals connecting side-branches of the abdominal aorta with the distal arterial limb. 4) These extensive collaterals adjacent to a chronic iliac av. fistula are demonstrated angiographically and by post-mortem vascular casts. 5) In all stages, occlusion of the proximal fistula artery simultaneously increases flow in the tail artery and contralateral iliac artery by more than 50%. This stresses the major contribution of these arteries to retrograde arterial fistula flow. 6) Successive occlusion of the tail artery and the contralateral iliac artery in stages II and III results in a nearly identical per cent decrease in "free" retrograde flow and in pressure (measured in the distal fistula artery). Even in the pre-fistula control stage, this occlusion experiment induces the same relative pressure-drop in the distal iliac artery. The proportional contribution of the collateral pathways to retrograde arterial fistula-flow and -pressure remains unchanged in the chronic stages post-fistula in spite of the tremendous expansion of collateral vessels within one year. These findings indicate that the three main collateral networks adjacent to the iliac artery all expand proportionally to their pre-fistula status in the months following construction of a large iliac av. fistula. This strongly suggests that the extensive interarterial anastomoses in a chronic av. fistula are all preformed collaterals which have gradually expanded.