Independent action of antidiuretic hormone, theophylline and cyclic 3',5'-adenosine monophosphate on cell membrane permeability in frog skin

Determination of the driving force of the Na(+) pump in toad bladder by means of vasopressin

Vasopressin stimulates Na(+) transport across toad bladder largely or entirely by decreasing the resistance to Na(+) entry into the transporting epithelial cells. Therefore, the hormone should induce proportional changes in short circuit current (I S ) and tissue conductance; the ratio of these changes should equal the driving force (E Na) of the Na(+) pump.Administration of vasopressin provided a rapid, reversible and reproducible technique for the measurement ofE Na. Values calculated forE Na ranged from 74 to 186 mV, in agreement with previously published estimates. The results were not dependent on the vasopressin concentration over a wide range of concentrations.Ouabain, an agent thought to inhibit specifically the Na(+) pump, decreased bothI S andE Na. On the other hand, amiloride, a diuretic thought to block specifically Na(+) entry, markedly reducedI S , without reducingE Na.It is concluded that vasopressin constitutes a probe for the rapid reproducible determination ofE Na under a wide variety of physiological conditions.

Effects of cyclic AMP and theophylline on chloride conductance across toad skin

1. The effects of the phosphodiesterase inhibitors theophylline and isobutylmethylxanthine (IBMX) on baseline and voltage-activated Cl- conductance (gCl) of toad skin were compared with those of the potent 2-chlorophenylthio analogue of cAMP (CPT-cAMP). 2. Using intact and split skins of Bufo viridis we confirmed that theophylline and IBMX raised the voltage-activated gCl with a pattern identical to that seen under control conditions. This effect was small or missing if gCl was already high in the control. 3. CPT-cAMP, in contrast, increased the Cl(-)-specific conductance by up to 6 mS cm-2 at short circuit. The characteristic time-dependent, slow activation of gCl by serosa-positive clamp potentials was completely lost under these conditions. 4. Coinciding with the loss of voltage activation of gCl the plateau value of the Lorentzian component of fluctuation in current at serosa-positive clamp potentials decreased by almost 50%. The corner frequencies were not notably different. 5. After CPT-cAMP, the sigmoidal voltage-conductance relation that is characteristic of control conditions or after theophylline disappeared; the patterns were variable and incompatible with voltage activation. 6. The voltage-activated gCl under control conditions and with theophylline was blocked by mucosal NO3-, I- or SCN-, the last two being almost equally effective. In the presence of CPT-cAMP, mucosal NO3- had minimal influence on tissue conductance, whereas the effects of I- and SCN- were essentially unchanged. Br- on the mucosal side could substitute for Cl- under all conditions. 7. The results suggest that protein phosphorylation by supramaximal concentrations of cAMP induces maximal conductance through anion-specific routes, while the voltage sensitivity of this pathway is lost. The effects of theophylline and IBMX on the voltage-activated Cl-conductance of toad skin cannot be explained solely by inhibition of the phosphodiesterase.

Metabolic inhibition and chloride transport in isolated toad skin

1. When added to the Na(+)-containing solution bathing the isolated toad skin, dinitrophenol (DNP, an uncoupler of oxidative phosphorilation) caused decreases in the baseline values of short circuit current (SCC) and transepithelial conductance (G). 2. DNP also inhibited the increases in SCC and G caused by theophylline, whether added prior to the xanthine, or after the effect of the latter was fully developed. 3. In skins exposed to theophylline and bathed in Cl(-)-free (sulfate Ringer's) solution, the changes in SCC and G had a similar time course (t1/2 > 15 min). In the presence of Cl- (skins bathed in Ringer's solution), SCC decreased with a similar rate, whereas the rate of the decrease in G was greater (t1/2 < 15 min). 4. DNP also decreased the SCC induced by a Cl- concentration gradient in skins exposed to theophylline (SCCg) with a time course similar to its effect on the theophylline-increased G in the presence of Cl-. DNP was effective irrespective of the presence of ambient Na+. 5. A similar difference was observed in skins bathed in CIR and exposed to forskolin. In contrast to theophylline, however, forskolin partially overcame the inhibition of G brought about by DNP; no such recovery was observed in SCC. 6. In contrast to its influence on the responses to theophylline and forskolin, DNP failed to prevent either the increase in G or the onset of SCCg in skins exposed to dibutyryl cyclic AMP. 7. Rotenone, an inhibitor of the electron-transport chain, significantly decreased SCC and G in the unstimulated skin. It also prevented the SCC response to theophylline, and decreased it if added after the effects of the xanthine were fully developed, but failed to modify the increase in G brought about by theophylline. The time course of SCC inhibition by rotenone was similar to that caused by DNP. 8. Ouabain, an inhibitor of Na+,K(+)-ATPase, decreased SCC in the theophylline-stimulated skin, without affecting G. 9. We conclude that, whereas integrity of oxidative energy metabolism is necessary to sustain SCC in the isolated toad skin, it is not a strict requirement for the increase of Cl(-)-dependent G activated by cAMP. 10. The effect of DNP on Cl(-)-dependent G activated by cAMP is probably exerted at the cAMP generation step, by inhibition of adenyl cyclase and/or a decrease in the availability of ATP.

Dynamics and density of mitochondria-rich cells in toad skin epithelium

The dynamics of change in mitochondria-rich (MR) cells density in the skin epithelium of Bufo viridis was studied on skin biopsies taken in vivo, throughout experimental periods lasting up to 3 months. When the bathing solution contained Cl-, MR cells' density (Dmrc) greatly decreased. There was one exception, when the acclimation solution was KCl, Dmrc in the skin increased. The rate of decrease in Dmrc depended on the mode of acclimation. When bath NaCl concentration was elevated slowly in small increments, the change in Dmrc was very slow. A regression line was calculated for the rate of decrease in the density of MR cells. An equation in the form of y = 1574 - 10.23x (where x = days; R2 = 0.626) was obtained with bath NaCl that was elevated from 30 to 200 mmol/l, in 45 days. Oxytocin (60 mU/ml) increased sodium transport, independently and without effect on Cl- conductance. Theophylline (1 mmol/l), which leads also to elevation of cellular cAMP in contrast, increased Na+ transport, but elevated Cl- conductance 3-4 times as well. Cl- conductance that is activated by transepithelial potential was much lower in skin from hyperosmotic NaCl-acclimated toads, as compared with that in skin from tap water-acclimated animals. Our experiments confirm that MR cells are a major pathway for Cl- conductance, as suggested earlier. However, the density of these cells in the skin epithelium of B viridis depends not only on bath NaCl concentration, but also on the mode of acclimation of the animals. Since transport functions other than gCl reside in the amphibian skin MR cells, the density of MR cells must also depend on these functions. These functions, and the mechanisms responsible for the down and up regulation of MR cells' density, remain to be established.

Cyclic AMP-and beta-agonist-activated chloride conductance of a toad skin epithelium

1. The control by intracellular cyclic AMP and beta-adrenergic stimulation of chloride conductance was studied in toad skin epithelium mounted in a chamber on the stage of an upright microscope. Impalement of identified principal cells from the serosal side with single-barrelled conventional or double-barrelled Cl(-)-sensitive microelectrodes was performed at x500 magnification. For blocking the active sodium current 50 microM-amiloride was present in the mucosal bath. 2. When clamped at transepithelial potential difference V = 0 mV, the preparations generated clamping currents of 0.9 +/- 1 microA/cm2 (mean +/- S.E.M.; number of observations n = 55). The intracellular potential of principal cells (Vb) was -96 +/- 2 mV with a fractional resistance of the basolateral membrane (fRb) of 0.016 +/- 0.003 (n = 54), and an intracellular Cl- activity of 40 +/- 2 mM (n = 24). 3. At V = 0 mV, serosal application of a cyclic AMP analogue, dibutyryl cyclic AMP (500 microM) or a beta-adrenergic agonist, isoprenaline (5 microM) resulted in a sixfold increase in transepithelial Cl- conductance identified by standard 36Cl- tracer technique. 4. The clamping current at V = 0 mV was unaffected by cyclic AMP (short-circuit current Isc = 0.1 +/- 0.3 microA/cm2, n = 16) indicating that subepidermal Cl(-)-secreting glands are not functioning in our preparations obtained by collagenase treatment. 5. Cyclic AMP- or isoprenaline-induced chloride conductance (Gcl) activation (V = 0 mV) was not reflected in membrane potential and intracellular Cl- activity in principal cells. Intracellular chloride activity was constant at approximately 40 mM at membrane potentials between -90 and -100 mV. Therefore, it can be concluded that the principal cells are not contributing to activated Cl- currents. 6. At V = -100 mV where the voltage-dependent chloride conductance of mitochondria-rich (MR) cells was already fully activated, GCl was unaffected by cyclic AMP or isoprenaline. The major effect of these treatments was a rightward displacement of the MR cell-generated GCl-V relationship along the V axis. 7. Our results indicate that the beta-adrenergically controlled cyclic AMP-mediated chloride conductance is localized to the mitochondria-rich cells.

Effect of theophylline on the electrolyte permeability of the isolated skin of the toad Bufo arenarum

1. Short-circuit current (SCC, an index of active sodium transport) increased in response to theophylline (Theo) in the isolated skin of Bufo arenarum, regardless of the presence of chloride in the bath. 2. Tissue conductance, G, and the transepithelial potential difference, PD, also increased moderately in skins bathed in chloride-free solutions (main anion: sulfate or iodide); the increases in SCC and G were fully blocked by further addition of amiloride to the epidermal bath. 3. The increase in G following theophylline was greater in the presence of chloride, whereas PD decreased; the increased G was not modified by amiloride at a concentration that completely abolished the SCC. 4. Establishment of a chloride gradient across the theophylline-treated skin whose SCC was completely abolished by amiloride or by removal of sodium from the bath, induced a diffusion current (SCCg) in a direction consistent with the transepithelial flow of chloride following its gradient. The intensity of the SCCg was directly related to the magnitude of the gradient. 5. For a given gradient, both the intensity of the SCCg and the increase in G were greater when the gradient was directed inward (i.e., when the chloride concentration was higher in the epidermal than in the dermal bath), as compared to the opposite case. 6. Exposure of the skin to an epidermal bath made hyperosmotic by addition of urea (epidermal hyperosmolarity, EH, which reversibly increases the permeability of the paracellular pathway by "opening" the tight junctions) induced similar increases in G, whereas SCC and PD decreased irrespective of the anion present in the solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of theophylline on the apical sodium and chloride permeabilities of amphibian skin

1. The effects of theophylline (1 mmol/l) on the sodium transport (short-circuit current, Isc) and transepithelial conductance (Gtotal) through toad (Bufo viridis) and frog (Rana temporaria and Rana esculenta) skin were investigated. 2. In toad skin incubated with nitrate Ringer solution on the apical side, theophylline induced an increase in Isc similar to that in frog skin bathed with chloride Ringer solution. 3. The increase in Isc could be attributed to recruitment of sodium channels, without affecting the single-channel current. 4. Chloride-bathed toad skin responded to theophylline with a large increase in transepithelial conductance, in addition to the increased Isc. 5. Chloride replacement by nitrate eliminated the effect of theophylline on the conductance increase, but the Isc response was even larger. 6. The results are discussed in relation to the localization of the cellular chloride pathway to the mitochondria-rich cells.

High [K+] alters the stimulus-hydrosmotic response coupling in toad bladder

Substitution of K+ for Na+ in the Ringer solution bathing the inner surface of toad urinary bladders (Bufo marinus) had no effect on basal water permeability but significantly altered the stimulus-hydrosmotic response of this epithelium. In chloride-Ringer, high [K+] increased the hydrosmotic responses to submaximal stimulations induced by vasopressin or exogenous cAMP, while the responses to theophylline or serosal hypertonicity were decreased. In sulfate-Ringer, all these responses were enhanced but for that induced by serosal hypertonicity which was actually diminished. As a step towards determining if Ca2+ might mediate the K+-induced effects on water flow, experiments were conducted either in the presence of a Ca2+ "antagonist" (cobalt) or in nominally Ca2+-free Ringer. In both conditions the hydrosmotic effects of vasopressin and cAMP were markedly reduced. The results raise the possibility that a transient Ca2+ influx through voltage-sensitive, Co2+-blockade Ca2+ channels may play a role in the stimulus-hydrosmotic response of toad urinary bladder.

Methylxanthines stimulate calcium transport and inhibit cyclic nucleotide phosphodiesterases in abalone sperm

Experiments were designed to determine the mechanism by which methylxanthines elevate abalone sperm cAMP concentrations and induce the acrosome reaction (AR). Theophylline or, more effectively, 1-methyl-3-isobutylxanthine (MIX) inhibit the cyclic nucleotide phosphodiesterase activities of abalone sperm homogenates. 45Ca2+ uptake by sperm is also stimulated by theophylline, and more effectively by MIX, and this stimulatory effect is blocked by KCN. Verapamil, a compound known to antagonize Ca2+ conductance, has no effect on the Ca2+ or MIX-induced cAMP elevation at concentrations up to 200 microM. However, verapamil reduces the sperm cAMP elevation caused by the addition of Ca2+ plus MIX. This inhibition is not complete, even at 200 microM verapamil. The AR induced by Ca2+ plus MIX is completely inhibited by 200 microM verapamil. The data suggest that these methylxanthines elevate abalone sperm cyclic nucleotide concentrations by inhibiting cyclic nucleotide phosphodiesterase activities. Furthermore, since sperm cAMP metabolism is modulated by Ca2+ flux, methylxanthines also appear to elevate abalone sperm cAMP concentrations by their effects on Ca2+ transport. The Ca2+-induced cAMP elevation occurs through a verapamil-insensitive mechanism, whereas the potentiation by MIX of the Ca2+ effect to elevate cAMP occurs through both verapamil-insensitive and -sensitive mechanisms. The methylxanthine-induced AR is mediated by a primary effect on Ca2+ transport and occurs through a verapamil-sensitive mechanism. Cyclic AMP may play a role in the methylxanthine-induced AR, but does not appear to act as the primary mediator of this exocytotic event.

Theophylline-induced stimulation of sodium transport in frog skin by a mechanism different from the antidiuretic hormone activated pathway

Theophylline (theo) induced a marked increase in the short circuit current (SCC) after maximal stimulation by the antidiuretic hormone, arginine vasotocin (AVT). The stimulation amounted to 20-70% of the AVT-stimulation. Practically no effect was seen on osmotic water flow after maximal AVT-stimulation. A concentration dependence of the SCC stimulation was found from 0.04 to 4 mM theo, 16 mM inhibited the SCC. The response to theo was independent of the time of preincubation with AVT. The theo induced increase of SCC was accounted for by active sodium transport. Theo did induce an increase in the cyclic AMP level after stimulation with a maximal concentration of AVT, but so did a supramaximal dose of AVT. This indicates that the mechanism, by which theo stimulated the SCC additional to maximal AVT stimulation, is different from that by which AVT works. This effect of theo may be unrelated to cAMP or it may be explained by differences in cellular specificity of theo and AVT.

The effects of theophylline and choleragen on sodium and chloride ion movements within isolated rabbit ileum

1. Theophylline (10 mM) and choleragen change the direction of net Cl- movements across rabbit ileum, in the short-circuit current condition, from absorption to secretion. The specific activity ratio R of Cl- tracers within the tissue coming from mucosal and serosal solutions respectively is increased, which is consistent with an increase in Cl- exchange flux across the mucosal border. 2. Net Na+ movement is also changed from net absorption to secretion by theophylline and choleragen; the specific activity ratio R of Na+ tracers is raised by theophylline. Because of the large paracellular component to transepithelial Na+ movements, an increase in Na+ exchange flux across the mucosal border is not detected. 3. 2,4,6-Triaminopyrimidine (20 mM) which has been previously shown to block paracellular Na+ movements, blocks both the theophylline and choleragen-dependent reversal of net Na+ movement by preventing the decrease in m-s Na flux. The theophylline-dependent increase in the ratio R of Na+ is still present, and is consistent with an increase in Na+ exchange flux across the mucosal border--unmasked by removal of the paracellular flux components. 4. Ouabain (0.1 mM) abolishes net absorption of Na+ and Cl- in control and net secretion of Na+ and Cl- in theophylline-treated tissue. Ouabain does not affect the theophylline-dependent increase in Cl- exchange across the mucosal border. 5. Replacement of Ringer Cl- with SO24- or Na+ by choline prevents the effects of theophylline and choleragen on Na+ and Cl- fluxes respectively. 6. Ethacrynate (0.1 mM) prevents the theophylline-dependent effects on net Na+ movement. Raising ethacrynate to 0.2 mM abolishes the effects of theophylline on Cl- exchange. An interpretation of these results is that theophylline and choleragen raise the Cl- permeability of the brush border. This increases NaCl leakage from the hypertonic lateral intercellular space into the mucosal solution thereby causing secretion. The selective action of triaminopyrimidine and ethacrynate (0.1 mM) on Na+ flux indicates that Na+ and Cl- move via separate transport pathways across the mucosal border.

Endogenous prostaglandins, adenosine 3':5'-monophosphate and sodium transport across isolated frog skin

1. Sodium transport across isolated frog skin, as measured by the short-circuit current, was decreased by acetylsalicylic acid, mefenamic acid, paracetamol and phenylbutazone. Indomethacin (6 X 10(-6) M) had a biphasic effect on the short-circuit current: a transient increase followed by a sustained decrease. 2. The release of prostaglandin-like material from the skin was reduced by acetylsalicylic acid and indomethacin. Paracetamol caused a significant reduction in the short-circuit current response of the skin to low doses of arachidonic acid, but the response to the highest dose tested was not significantly altered. 3. Indomethacin (6 X 10(-6) M) increased the sensitivity of the skin to applied prostaglandin E1. The other prostaglandin synthetase inhibitors did not have this effect. Indomethacin (6 X 10(-6) M) also enhanced the effect of antidiuretic hormone on the short-circuit current. 4. Indomethacin (30 X 10(-6) M) increased the short-circuit current and diminished the response to applied prostaglandin E1. 5. In sulphate Ringer, theophylline increased the short-circuit current and diminished the response to prostaglandin E1. 6. Prostaglandin E1 increased the levels of cyclic AMP in frog skin and these increases preceded the increases in short-circuit current. There was a seasonal variation in the level of cyclic AMP in the skin: the levels in winter exceeded those in summer. There was also a seasonal variation in the cyclic AMP response to prostaglandin E1: the winter response was greater than that in summer. 7. Indomethacin (6 X 10(-6) M) had a biphasic effect on cyclic AMP levels in the skin, an initial increase followed by a decrease. Indomethacin also potentiated prostaglandin E1 stimulated cyclic AMP accumulation. 8. Theophylline increased cyclic AMP levels in the skin and potentiated prostaglandin E1 stimulated cyclic AMP accumulation. 9. Pre-treatment of the skin with theophylline reversed the effects of cyclic AMP on the short-circuit current and open-circuit potential. 10. It is concluded that endogenous prostaglandins help to maintain sodium transport across isolated frog skin and that the effects of E-type prostaglandins on the short-circuit current are mediated by increased cyclic AMP levels. The transient increase in short-circuit current and the increased skin sensitivity caused by indomethacin (6 X 10(-6) M) are attributed to inhibition of phosphodiesterase activity. The failure of theophylline to potentiate the short-circuit current response of the skin to prostaglandin E1 is attributed to alteration of cyclic AMP action on the skin by theophylline.

Variation in the effects of antidiuretic hormone on the isolated skin of the toad, Scaphiopus couchi

The rate of active sodium transport as measured by short-circuit current across the isolated skin of the toad, Scaphiopus couchi, was elevated following vasopressin (0.2 units/ml) or arginine vasotocin (0.1 units/ml) treatment of skins from active animals at all times of the year tested. Skins from dormant animals showed no such elevation at any time of the year. The rate of active sodium transport was elevated following treatment with dibutyryl cyclic AMP (2.5mM) plus theophylline (10 mM) in all skins tested. The hydraulic conductivity of isolated skins from both active and dormant animals showed no significant change following treatment with vasopressin (0.2 units/ml) or arginine vasotocin (0.1 units/ml except on the first day following emergence from dormancy in the field. A correlation was, therefore, observed between the occurrence of a hydroosmotic response to antidiuretic hormones and the seasonal exposure of S. couchi to standing water. A small but significant elevation of hydraulic conductivity was observed across the skins of dormant toads following treatment with dibutyryl cyclic AMP (2.5 mM) plus theophylline (10 mM) whereas a substantial elevation was observed with the skins of active animals.

The membrane action of antidiuretic hormone (ADH) on toad urinary bladder

Radioactive tracer and electrical techniques were used to study the transport of nonelectrolytes and sodium, respectively, across toad urinary bladders in the presence and absence of ADH. The permeability of lipophilic molecules was roughly proportional to bulk phase oil/water partition coefficients both in the presence and absence of hormone; i.e., ADH elicited a general nonselective increase in the permeation of all nine solutes tested. The branched nonelectrolyte, isobutyramide, was less permeable than its straight-chain isomer, n-butyramide, in control tissues. ADH reduced the discrimination between these structural isomers. Hydrophilic solutes permeated more rapidly than expected. In the presence of hormone, there was no change in the permeation of large hydrophilic solutes considered to move via an extracellular pathway, but there was a marked increase in the permeability of water and other small hydrophilic solutes. Collectively, these results suggest that ADH acts to increase the motional freedom or fluidity of lipids in the cell membrane which is considered to be the preferred pathway for the permeation of lipophilic and small hydrophilic molecules. At concentrations of cAMP and ADH which elicit equivalent increments in the shortcircuit current, the effects of these agents on nonelectrolyte transport and membrane electrical conductance are divergent. Such observations suggest that some membrane effects of ADH may not be directly dependent upon cAMP. ADH in the mucosal solution increased the permeability of the toad bladder when the surface charge on the outer surface of the apical membrane was screened with the polyvalent cation, La-3+. These experiments emphasize that interaction of ADH with membranes of toad urinary bladder may account for at least some effects of this hormone.

Actions of external hypertonic urea, ADH, and theophylline on transcellular and extracellular solute permeabilities in frog skin

Increases in transepithelial solute permeability were elicited in the frog skin with external hypertonic urea, theophylline, and vasopressin (ADH). In external hypertonic urea, which is known to increase the permeability of the extracellular (paracellular) pathway, the unidirectional transepithelial fluxes of Na (passive), K, Cl, and urea increased substantially while preserving a linear relationship to each other. The same linear relationship was also observed for the passive Na and urea fluxes in regular Ringer and under stimulation with ADH or 10 mM theophylline, indicating that their permeation pathway was extracellular. A linear relationship between Cl and urea fluxes could be demonstrated if the skins were separated according to their open circuit potentials; parallel lines were obtained with increasing intercepts on the Cl axis as the open circuit potential decreased. The slopes of the Cl vs. urea lines were not different from that obtained in external hypertonic urea, indicating that this relationship described the extracellular movement of Cl. The intercept on the ordinate was interpreted as the contribution from the transcellular Cl movement. In the presence of 0.5 mM theophylline or 10 mU/ml of ADH, mainly the transcellular movement of Cl increased, whereas 10 mM theophylline caused increases in both transcellular and extracellular Cl fluxes. These and other data were interpreted in terms of a possible intracellular control of the theophylline-induced increase in extracellular fluxes. The changes in passive solute permeability were shown to be independent of active transport. The responses of the active transport system, the transcellular and paracellular pathways to theophylline and ADH could be explained in terms of the different resulting concentrations of cyclic 3'-5'-AMP produced by each of these substances in the tissue.

Effects of furosemide on sodium content and transport pool in frog skin (Rana esculenta): comparison with vasopressin and ouabain

The effects of ouabain, vasopressin, and furosemide on intracellular concentrations of total sodium([Na]) and potassium [K]), on exchangeable sodium ([Na]) and the sodium transport pool ([Nap]) were investigated in isolated short circuited skins of rana esculenta. Furosemide was added to the epithelial bathing solution, vasopressin and ouabain to the corial bathing solution. Results were compared with the amount of net sodium transport measured by short circuit current (scc). Ouabain reduces scc and increases [Na] and [Na]; [K] is decreased. The administration of vasopressin leads to a sharp increase of scc, combined with an enhancement of of [Na] and [Na]; [K] shows no significant change. [Nap] is significantly increased, too, and approximately to the same amount as [Na]. Furosemide causes an increase of scc, whereas a significant change of [Na], [Na] and [K] could not be detected. On the other hand, [Nap] was enhanced significantly. The results support the hypothesis that furosemide like vasopressin is acting by increasing the entry of sodium into the transport compartment of the active cell layer. The result is an increased transfer of sodium across the skin.

Calcium release in relation to permeability changes in toad bladder epithelium following antidiuretic hormone

1. Methods for measuring the release of (45)Ca from isolated urinary bladders of toads (Bufo marinus) pre-loaded with this isotope have been devised. One method allowed separate collection from the mucosal and serosal surfaces of the bladders.2. Reducing the ambient calcium concentration reduced the rate of (45)Ca efflux suggesting that efflux of radiolabel represents calcium exchange.3. Antidiuretic hormone, theophylline and prostaglandin E(1) all increased calcium efflux, while lanthanum and amphotericin were without effect. Cyclic AMP caused only an inhibition of calcium release.4. The increase in (45)Ca efflux due to antidiuretic hormone came exclusively from the mucosal side. Experiments with EGTA suggest that the calcium entering the mucosal solution arises mainly from superficial sites in the mucosal membrane.5. The release of (45)Ca by hormone was not influenced by removal of sodium from the bathing solution. Low pH and amiloride reduced or abolished calcium release to hormone.6. The time course of calcium release from the mucosal surface due to hormone was rapid (commencing between 0.5 and 1.5 min after hormone application). Thus calcium release precedes the increase in sodium transport and hydro-osmotic flow following hormone, and appears to be at least as rapid as cyclic AMP generation in the tissue.7. The relationship between calcium release or exchange and the permeability changes in the bladder to water and to sodium, following hormone, are discussed.

The actions of dibutyryl cyclic adenosine 3',5'-monophosphate and methyl xanthines on pancreatic exocrine secretion

1. The effects of dibutyryl cyclic adenosine 3',5'-monophosphate (dibutyryl cyclic AMP) and theophylline have been tested in the stimulated and unstimulated perfused cat pancreas.2. Dibutyryl cyclic AMP (1.0 mM) elicited the secretion of water and electrolytes, but not of enzymes, from this preparation. The composition of this secretion was the same as that secreted in response to secretin. This response could be slightly potentiated by theophylline.3. Theophylline, theobromine and caffeine all markedly potentiated submaximal secretin stimulation, the relative effectiveness of these methyl xanthines being the same as that observed in the inhibition of pure phosphodiesterase prepared from beef heart.4. At high concentration, theophylline had two effects: it was capable of initiating electrolyte and water secretion alone (whilst having only a very small stimulatory effect on enzyme secretion); it also had an inhibitory effect on secretion stimulated maximally by secretin.5. Thus it was easy to mimic the action of secretin, but not pancreozymin, using dibutyryl cyclic AMP and theophylline. This suggests that the action of secretin, but not that of pancreozymin, may be mediated through cyclic AMP. Further evidence is, however, needed before these conclusions can be made with confidence.

Some aspects of the inhibition of the action of antidiuretic hormone by lithium ions in the rat kidney and bladder of the toad Bufo marinus

1. The effect of intravenous infusions of various ions on the antidiuretic action of antidiuretic hormone has been studied in rats.2. Lithium (13 mmol/l.) reversibly inhibits the antidiuretic responses. Similar concentrations of potassium, rubidium, strontium, magnesium, choline and calcium do not. Lithium has a similar effect on the antidiuretic activity of oxytocin.3. The inhibition is not simply related to blood nor whole body lithium concentrations.4. Lithium (2 mmol/l.) in contact with the serosal surface also inhibits the transport of water facilitated by either 0.5 U/l. antidiuretic hormone or 1.1 mmol/l. cyclic adenosine monophosphate in the isolated toad bladder.5. Choline (2 mmol/l.) on the serosal surface also inhibits the transport of water facilitated by vasopressin in the toad bladder.

Sodium transport across the isolated epithelium of the frog skin

1. A method to separate the epithelium from the underlying layers of the frog skin is described. The method is based on the combined use of collagenase and hydrostatic pressures.2. The potential difference and the short-circuit current values of isolated epithelia and whole skins are similar. Na net flux and short-circuit current are equivalent.3. The time course of changes in potential following rapid changes in composition of the bathing solutions shows that the barrier to K diffusion at the internal surface of the isolated epithelium is larger than the barrier to Na diffusion at the external surface.4. In the isolated epithelium there are 133 m-mole K(+) and 24.7 m-mole Na/l. cellular water. The amount of extracellular water was considered to be equal to the inulin space.5. Arginine vasopressin (0.1 u./ml.) markedly increased short-circuit current and potential difference in isolated epithelia. The amount of Na in the epithelium that equilibrated with Na in the external solution was not increased by the hormone.6. Ouabain (10(-4)M) reduced short circuit current and potential difference to values close to zero. The ouabain treated epithelia contained an increased amount of Na originating in the internal solution. On the other hand the amount of Na that originated from the external solution was not increased.7. The amount of epithelial Na that equilibrated with Na in the external solution was 0.009 mu-equiv/cm(2). This figure is about ten times smaller than the values found in whole skins.

Capacitance changes in frog skin caused by theophylline and antidiuretic hormone

1. Impedance loci for frog skins have been calculated by computer analysis from voltage transients developed across the tissues.2. Attention has been paid to simultaneous changes in conductance and capacitance of skins treated either with antidiuretic hormone (ADH) or with theophylline. These drugs always caused an increase in conductance and usually the skin capacitance also increased. However, changes in conductance were not correlated with capacitance changes.3. Changes in capacitance caused by the drugs may represent pore formation in the barrier to water flow, since both drugs increase hydro-osmotic flow in epithelia. If this interpretation is correct, then 0.14% of the membrane area forms water-permeable pores in response to a maximal dose of ADH. This value is somewhat less than the value obtained previously (0.3%) by graphical analysis.4. A theoretical account is given of the relative accuracy of the computer method and the graphical method for voltage transient analysis.

From frog skin to sheep rumen: a survey of transport of salts and water across multicellular structures

All higher animals, whether they live in water or on dry land, are faced with the necessity of regulating rather closely their intake and excretion of salts and water in order to maintain the constancy of their internal ionic environment. The kidney is in general the most important organ of the body as far as the excretion of sodium, potassium, chloride and water is concerned, but there are other tissues which also play a part in controlling the ionic balance between the internal and external environments, such as the intestinal mucosa, the skin and urinary bladder in amphibia, the gill epithelium in fishes, the salt gland in marine birds, and the epithelium of the rumen in ruminants. In addition to excretory and absorptive organs of this type, there are others which are secretory and whose function involves the production of fluids differing in ionic composition from the blood plasma. Examples include the glands which secrete saliva and sweat, the oxyntic acid-producing cells of the gastric mucosa, and the epithelium of the stria vascularis which generates the potassium-rich endolymph of the mammalian cochlea. The purpose of this article is to consider briefly what is known about the active transport of salts and water across some typical multicellular secretory tissues, and to attempt in the process to discern what properties they have in common and in what respects they are specialized.

Stimulation of anterior pituitary adenyl cyclase activity and adenosine 3':5'-cyclic phosphate by hypothalamic extract and prostaglandin E1

Hypothalamic extract, containing the releasing factors for anterior pituitary hormones, within minutes stimulated adenyl cyclase activity and adenosine 3':5'-cyclic phosphate (cyAMP) concentrations in rat anterior pituitary in vitro. Cerebral cortical extract was ineffective and hypothalamic extract had no effect on these parameters in posterior pituitary or thyroid. Prostaglandin E(1) also increased adenyl cyclase activity and cyAMP levels in anterior pituitary tissue. Although NaF augmented adenyl cyclase activity, it did not elevate cyAMP. Epinephrine, norepinephrine, histamine, serotonin, dopamine, and vasopressin did not increase either adenyl cyclase or cyAMP. The increased adenyl cyclase and cyAMP produced by hypothalamic extract was associated with greater luteinizing hormone release from anterior pituitary in vitro.

The effects of anions on sodium transport

1. Substitution of chloride by isethionate reduces the short circuit current (SCC) and increases the potential of isolated frog skin. In sodium isethionate Ringer antidiuretic hormone and choline chloride increase the SCC, whereas theophylline is ineffective.2. Frog skins treated on the outside with copper ions always show an increased potential when bathed in normal Ringer solution. The SCC may be moderately increased or decreased.3. Theophylline increases skin thickness and cell volume in non-short-circuited skins.4. The ways in which the theophylline-induced increase in chloride permeability affects sodium transport is discussed, together with the requirements for a permeant anion in both short- and open-circuited skins.