Ion transport regulation by prostaglandins in mouse macrophages

Although the prostaglandins PGE1, PGE2 and PGF2 alpha had no effect on ion transport in isolated human erythrocytes, they modulated ion transport in isolated mouse macrophages, apparently through the mediation of cAMP, by inhibiting the NA+, K+ cotransport system, stimulating the Na+, K+ pump, and stimulating the Na+: Ca++ exchange mechanism.     

The use of isolated fish opercular epithelium as a model tissue for studying intrinsic activities of loop diuretics

Isolated opercular epithelia of killifish (Fundulus heteroclitus) were mounted in an Ussing chamber. The epithelia displayed a transepithelial electrical potential difference (PD) of 10.6 +/- 0.3 mV (sea-water side negative) and a short-circuit current (SCC) of 72.1 +/- 2.1 microA cm-2. The electrical resistance was 160 +/- 3 omega cm2 (mean +/- SE, n = 269). The unidirectional flux of 36Cl from blood side to sea-water side compared well with the SCC. No net flux of 22Na or 24Na across the epithelium was observed. Raising of cyclic AMP levels by theophylline, 3-isobutyl-I-methyl-xanthine, isoprenaline and forskolin, increased SCC and PD. Prostaglandins PGE2 and to some extent PGF2 alpha inhibited SCC and PD. Inhibition of Na+-K+-ATPase by ouabain and orthovanadate reduced SCC and PD. Pretreatment of the epithelium with the stilbene disulphonic acid (DIDS) did not prevent the action of orthovanadate. Different types of diuretics were tested, but only the loop diuretics bumetanide, piretanide, and furosemide, rapidly and strongly inhibited PD and SCC and unidirectional 36Cl serosal to mucosal flux. Dose-response curves for these agents were parallel and EC50 values for effects on SCC were 40, 52, and 295 microM, respectively. The same relative activities of these diuretics have been seen in the renal thick ascending limb of Henle's loop (TALH). It is concluded that the killifish opercular skin responds to hormonal stimuli and various pharmacological agents in a manner similar to that of mammalian renal TALH. It should therefore be a useful model for studies of the modes of action and the structure-activity relationships of diuretics which act by inhibition of chloride transport or Na+-K+-ATPase activity.     

Chloroquine stimulates absorption and inhibits secretion of ileal water and electrolytes

The effects of chloroquine diphosphate, a drug with "'membrane-stabilizing" properties, were studied on basal ileal absorption and on ileal secretion induced by increased intracellular cAMP levels and calcium (serotonin). The studies were performed on rat (in vivo) and rabbit ileum (in vitro). Intraluminal chloroquine (10(-4) M) reversed cholera toxin- and theophylline-induced secretion in rat ileum but did not alter the cholera toxin- and theophylline-induced increases in cAMP content. Addition of chloroquine (10(-4) M) to the mucosal surface of rabbit ileum did not alter basal active electrolyte transport or the serotonin-induced decreased Na and Cl absorption but inhibited the theophylline-induced C1 secretion. Addition of chloroquine (10(-4)) M) to the serosal surface stimulated net Na and Cl absorption. This effect may involve intracellular calcium. Chloroquine increased the rabbit ileal calcium content and decreased 45Ca2+ influx from the serosal surface. Both the mucosal and serosal effects of chloroquine described led to a net increase in absorptive function of the intestine and should prove useful in developing treatment of diarrheal diseases.     

Effect of ventilatory rate on renal venous PGE2 and PGF2 alpha efflux in anesthetized dogs

In anesthetized laparotomized male mongrel dogs with ventilatory rate set at 10 breath.min-1, tidal volume was adjusted so that control arterial pH and PCO2 were within the normal range for unanesthetized dogs. Control renal venous PGE2 and PGF2 alpha concentrations were comparable to those of unanesthetized dogs, namely, 57 +/- 10 and 114 +/- 18 pg.ml-1, respectively. In contrast, control arterial plasma renin activity (PRA), 6.6 +/- 1.2 ng.ml-1.h-1, was considerably greater than in unanesthetized dogs. Stepwise increases in ventilatory rate increased renal venous PGE2 and PGF2 alpha to 109 +/- 18 and 205 +/- 41 pg.ml-1, respectively. Hyperventilation reduced PCO2 and increased pH and PRA but had no effect on renal blood flow, arterial blood pressure, or arterial PGE2 and PGF2 alpha concentrations. When the ventilatory rate was returned to control levels, pH, PCO2, PRA, and renal venous PGE2 and PGF2 alpha concentrations returned to control. Ventilatory rate or some consequence of altering ventilatory rate is, therefore, a determinant of renal venous efflux of PGE2 and PGF2 alpha. Moreover, it may be a more important determinant of "resting" concentrations of prostaglandins in renal venous blood than anesthesia, laparotomy, or PRA.     

Comparison of PGE2, 6-keto PGF1 alpha and renin release from dog kidneys

Several renal cell types synthesize prostaglandin E2 (PGE2) and prostacyclin (PGI2). To examine whether the release of these prostaglandins varies in proportion, prostaglandin synthesis was stimulated in anaesthetized dogs by renal arterial constriction, ureteral occlusion, intrarenal angiotensin II infusion and infusion of arachidonic acid, the precursor of PG synthesis. PGI2 was measured as its stable hydrolysed product, 6-keto PGF1 alpha. The two former procedures raised PGE2 release to 13 +/- 2 pmol min-1, 6-keto PGF1 alpha release to 5 +/- 2 pmol min-1 and renin release to 23 +/- 5 micrograms AI min-1. Angiotensin II infusion, reducing the renal blood flow by 30%, increased PGE2 and 6-keto PGF1 alpha release only half as much as ureteral and renal arterial constriction, and exerted no significant effect on renin release. By increasing the infusion rate of angiotensin II up to 10 times, the renal blood flow remained unaltered in four dogs and fell to 50% of control in two dogs, but PGE2 and 6-keto PGF1 alpha release did not increase further in any of the experiments. Arachidonic acid, infused at 40 and 160 micrograms kg-1 min-1, increased prostaglandin release in proportion to the infusion rate. At the highest infusion rate, PGE2 release averaged 166 +/- 37 pmol min-1 and 6-keto PGF1 alpha release 98 +/- 28 pmol min-1. All procedures increased PGE2 and 6-keto PGF1 alpha release in a fixed proportion of about 2.5:1, whereas renin release increased only during autoregulatory vasodilation.     

Prostaglandin D2 increases Cl secretion across canine tracheal epithelium through cyclo-oxygenase stimulation and cAMP production.

Prostaglandin (PG) D2 is one cyclo-oxygenase product of arachidonic acid metabolites that may play a role in the pathogenesis of asthma. To determine the effect of PGD2 on ion transport by airway epithelium and its mechanism of action, we measured bioelectric properties of canine cultured tracheal epithelium under short-circuit conditions in vitro. PGD2 (10(-7) M) increased short-circuit current (Isc) from 5.5 +/- 1.2 to 14.1 +/- 2.9 microA cm-2 (means +/- SE, P less than 0.01) when added to the mucosal solution, and to 22.2 +/- 3.8 microA cm-2 (P less than 0.001) when added to the submucosal solution, an effect that was accompanied by the corresponding increases in transepithelial potential difference and conductance. These effects were dose-dependent. The PGD2-induced increase in Isc was not altered by preincubation of cells with autonomic antagonists (phentolamine, propranolol, atropine), the lipoxygenase inhibitor AA-861, the protein kinase C inhibitor H-7, or the Na channel blocker amiloride, but it was inhibited by each of indomethacin, piroxicam, the Cl channel blocker diphenylamine-2-carboxylate, the Cl transport inhibitor furosemide, and Cl-free medium. Intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels were dose-dependently increased by PGD2. These results suggest that PGD2 may selectively stimulate airway epithelial Cl secretion via cyclo-oxygenase- and cAMP-dependent pathway.     

α2-Adrenoceptors inhibit antidiuretic hormone-stimulated Na+ absorption across tight epithelia (Rana esculenta)

In the present study we examined the effect of alpha-adrenergic regulation of active transepithelial Na+ absorption across the isolated frog skin epithelium. alpha-Adrenergic stimulation was achieved by addition of the adrenergic agonist noradrenaline in the presence of the beta-adrenergic blocker propranolol. alpha-Adrenergic stimulation inhibited basal as well as antidiuretic hormone (ADH)-stimulated Na+ transport. The ADH-induced increase in Na+ transport was accompanied by a membrane depolarisation due to an increase in the apical Na+ permeability. The subsequent application of noradrenaline inhibited the Na+ transport and repolarised the membrane potential, suggesting that alpha-adrenergic stimulation had reduced the apical Na+ permeability. The inhibition was abolished by the alpha2-adrenergic antagonist yohimbine whereas it was insensitive to the alpha1-adrenergic antagonist prazosin. alpha-Adrenergic stimulation had no effect on the cytosolic free [Ca2+] ([Ca2+]i). Incubation of the epithelium in the presence of ADH increased the cellular adenosine 3',5'-cyclic monophosphate (cAMP) content, an increase which was abolished by alpha-adrenergic activation. The effect of alpha-adrenergic stimulation on cAMP production was abolished by the alpha2-adrenergic antagonist yohimbine. We conclude that the noradrenaline-induced inhibition of the ADH-stimulated Na+ absorption and cAMP content is mediated by activation of alpha2-adrenoceptors. The data further indicate that the principal cells of the epithelium do not express alpha1-adrenoceptors. The noradrenaline-induced inhibition of the ADH-stimulated Na+ transport was concentration dependent, with 0.24+/-0.03 microM eliciting a half-maximal response. This alpha2-adrenergic-mediated down-regulation of Na+ absorption is achieved at a concentration of noradrenaline which begins to activate the NaCl secretion via the skin glands. The alpha2-adrenoceptors therefore appear to have considerable physiological importance.     

Influence of prostaglandins and a prostaglandin H synthase inhibitor on cervical secretion of the guinea-pig.

The modulatory effects of several prostaglandins and a prostaglandin H synthase inhibitor (indomethacin) on basal as well as nerve stimulation induced secretion from the cervical glands of the guinea-pig were studied. Hypogastric nerve stimulation resulted in a secretory response of +113%. Indomethacin dose dependently inhibited this secretory response. Prostaglandins E2, F2 alpha and I2 inhibited and 19-OH prostaglandin E1 reduced nerve stimulation induced secretion. Prostaglandin I2 and 19-OH PGE1 markedly enhanced basal secretion, while indomethacin as well as PGE2 and PGF2 alpha did not induce any secretion of cervical glands. However, PGF2 alpha in combination with the alpha-adrenergic blocker phentolamine resulted in an increase in secretion. The inhibitory effect of prostaglandins on cholinergic secretory innervation might be due to stimulation of adrenergic nerves exerting an inhibitory influence on cholinergic secretomotor innervation. It is suggested that PGI2 and 19-OH PGE1 exert postjunctional stimulatory effects on the secretory lining and that a lack of secretory effect of PGF2 alpha at least in part may be due to stimulatory effects on adrenergic neurons, inhibiting cholinergic secretomotor transmission. Thus, in this in vitro study it is shown that metabolites of the arachidonic acid cascade and a prostaglandin H synthase inhibitor can modulate cervical secretion and thus maybe influence fertilization.     

The effect of ouabain on ion transport across isolated sheep rumen epithelium.

1. The net flux of Na from the lumen to the blood side of isolated sheep rumen epithelium was reduced to zero in the third 30 min period after treatment with ouabain. 2. The net flux of K from blood to lumen side of the epithelium was reduced from 0-34 to 0-13 mumole/cm2. hr in the third 30 min period after ouabain treatment. 3. The net flux of Cl from lumen to blood side of the epithelium was reduced from 1-4 to 0-72 mumole/cm2. hr in the third 30 min period after ouabain treatment. 4. The results support the existence of a Cl pump independent of Na transport and also a K pump in sheep rumen epithelium.     

Transport and electrical phenomena in resting and secreting piglet gastric mucosa.

1. Gastric mucosae were isolated from piglets (0-5 days old) and mounted in a chamber where electrical properties and secretory function could be measured. Unlike many previously reported mammalian in vitro preparations, pig gastric mucosae were stable and physiologically responsive for many hours after isolation. 2. With similar Ringer solutions bathing both surfaces, the isolated piglet gastric mucosa maintained a p.d. with the mucosal surface 30-35 mV negative with respect to the serosal surface. Limitation of access of Na+ from the mucosal bathing solution to the tissue (e.g. replacement of Na+ on mucosal side with choline or treatment with 10- minus 5 M amiloride) produced a decrease in p.d. and increase in mucosal resistance consistent with an hypothesis of Na+ transport from mucosa to serosa. 3. Isotopic flux measurements (36Cl and 24Na) and net H+ secretory rate were performed during open and short-circuit conditions, while the tissue was at rest and after stimulation of HCl secretion by 6 times 10- minus 5 M histamine. Up to 90% of the respective short-circuit current for resting or secreting mucosae was accounted for as the algebraic sum of Cl minus, H+ or Na+ fluxes. 4. The net transport of Na+ which occurred from mucosa to serosa during rest (ca. 4-7 muequiv/cm2.hr) was somewhat reduced during HCl secretion (ca. 2-7 muequiv/cm2.hr). This active transport of Na+ was more resistant to anaerobiosis than was H+ or Cl minus transport. 5. An active transport component of Cl minus from serosa to mucosa was clearly demonstrable in the non-secreting preparations (ca. 3-9 muequiv/cm2.hr). Active Cl minus transport was stimulated three- to fourfold after H+ secretion was stimulated by histamine. Anaerobiosis promptly reduced Cl minus and H+ transport. An exchange diffusion component was demonstrated for Cl minus which appeared to be prominent during H+ secretory activity and was considerably diminished in resting mucosae. 6. Large changes in mucosal resistance were associated with conditions of rest, histamine stimulation and anaerobic conditions; mean values were 113, 74 and 197 omega.cm2, respectively. Electrical conductance of the isolated gastric mucosa was due primarily to partial ionic conductance of Cl minus (60-65%) and Na+ (10-15%). The partial conductance of H+ was extremely low. The observed increase in tissue conductance associated with H+ secretory activity and the changes in the long-time constant p.d. transient to a current pulse are discussed in terms of the relative contribution of the serosal and mucosal plasma membrane surfaces.     

Effects of platelet-activating factor on bioelectric properties of cultured tracheal and bronchial epithelia

To elucidate the effect of platelet-activating factor (PAF) on ion transport function of airway epithelial cells, we studied bioelectric properties of cultured tracheal and bronchial epithelia from dogs under short-circuit conditions in vitro. Addition of PAF (10(-5) mol/L) to mucosal solution of Ussing chamber increased short-circuit current of tracheal epithelium from 3.3 +/- 0.7 to 8.5 +/- 1.2 microA/cm2 (p less than 0.001). This effect was dose dependent, and there was a corresponding increase in transepithelial potential difference. In contrast, PAF was without effect when it was added to the submucosal side. Electrical properties of bronchial epithelium remained unchanged by PAF. The PAF-induced increase in short-circuit current was not affected by amiloride but abolished by diphenylamine-2-carboxylate, bumetanide, or Cl-free medium. The effects of PAF were not altered by AA-861 or U-60257, but attenuated by indomethacin and piroxicam, and dose-dependently blocked by CV 6209 and WEB 2086. Mucosal, but not submucosal, addition of PAF increased the rate of prostaglandin release from tracheal epithelium. These results suggest that PAF selectively stimulates Cl secretion across tracheal epithelium, probably through activation of its specific receptors and the subsequent production of prostaglandins.     

Regulatory role of cAMP in transport of Na+, Cl- and short-chain fatty acids across sheep ruminal epithelium

Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short-chain fatty acids (SCFAs). However, regulation of ruminal Na+, Cl-, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodium-coupled transport mechanisms in short-circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mM) or theophylline in combination with forskolin (0.1 mM) significantly reduced mucosal-to-serosal sodium transport, leading to a reduction of net transport. The theophylline- or theophylline-forskolin-induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short-chain fatty acids stimulated Na+ transport but their stimulatory effect was almost completely blocked by theophylline-forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mM amiloride on sodium transport was strongly reduced after theophylline-forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 microM) led to a theophylline-sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride-sensitive Na+-H+ exchange and/or basolateral Na+-K+-ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions.     

Mechanism of electrically silent Na and Cl transport across the rumen epithelium of sheep

This study was designed to study the mechanism of electroneutral Na and Cl transport across the isolated rumen epithelium of sheep. Net sodium transport (5.75 +/- 0.35 microequiv cm-2 h-1) was significantly higher than the short-circuit current (0.95 +/- 0.08 microequiv cm-2 h-1). Both, net sodium and net chloride transport were markedly reduced by replacement of chloride, bicarbonate and sodium, respectively, but were not changed by the absence of mucosal potassium. Net sodium and net chloride absorption was significantly decreased by 1.0 mM-amiloride. Mucosal addition of bumetanide, furosemide, hydrochlorothiazide or low concentrations of amiloride (less than 0.1 mM) did not change sodium fluxes. These results provide compelling evidence consistent with the presence of Na-H exchange as the predominant electroneutral mechanism for transepithelial sodium movement. The ion replacement studies and data from literature suggest that the Na-H exchange is working in parallel with a Cl-HCO3 exchange although luminal addition of DIDS (4,4'diisothiocyanatostilbene-2,2'-disulphonate, 1 mM) did not significantly influence Cl transport.     

Effects of methylprednisolone on electrolyte transport by in vitro rat ileum

Administration of the glucocorticoid methylprednisolone (MP) (30 mg/kg body wt for 3 days) to rats increased intestinal mucosal guanylate cyclase and Na-K-ATPase activities, short-circuit current (Isc), electrical potential difference (PD), net Na absorption, and net Cl secretion and reversed HCO3 transport from secretion to absorption. In the MP-treated animals, removal of HCO3 from both the mucosal and serosal bathing solutions increased Cl secretion but did not alter the Isc, PD, and net Na flux. Removal of Cl abolished the MP-induced increase in Isc but did not affect the MP-induced changes in net Na and HCO3 fluxes. At 6 h, after a single dose of MP, stimulation of guanylate cyclase activity was already maximal, whereas Na-K-ATPase activity was not detectably altered. The changes in intestinal transport properties present 6 h after MP treatment and associated with the increased guanylate cyclase activity were an increase in Isc and PD and a reversal of net Cl absorption to net secretion. These results suggest that an initial response to MP administration is a persistent increase in intestinal guanylate cyclase activity that mediates an electrogenic Cl secretory process, then is followed by a superimposed effect of increased Na-K-ATPase activity that mediates an increase in net Na absorption.     

Mechanism of calcium ionophore stimulated Cl secretion from frog skin glands

The aim of the present study was to investigate the mechanism by which the calcium ionophore A23187 stimulates Cl and water secretion from exocrine glands in the frog skin. The Cl secretion was visualized as changes in short-circuit current (SCC) in skins where the Na absorption was blocked by amiloride applied to the apical membrane. Measurements of A23187 stimulated ion fluxes showed that the ionophore induced a net secretion of Cl, Na and K. The active Cl secretion was enhanced more than the Na and K secretion, resulting in a net secretion of negative ions which closely resembled the A23187-stimulated SCC. The effect of A23187 was abolished in skins pretreated with indomethacin, implying the involvement of prostaglandins in the response. Furthermore, the effect of A23187 was inhibited in the presence of quinacrine, indicating that the activation of the cyclooxygenase pathway is dependent on phospholipase A₂ activity. In addition, the A23187, but not the arachidonic acid stimulated Cl secretion was abolished in the presence of trifluoperazine, suggesting that the effect of the ionophore may be mediated via a Ca²⁺-calmodulin-dependent step located before the activation of the cyclooxygenase. The net water flow and the Cl secretion were measured simultaneously under the conditions outlined above. The stimulation, inhibition, and time-course of the water secretion were similar to the changes observed for the Cl secretion. The A23187 stimulated Cl secretion was enhanced by the phosphodiesterase inhibitor, theophyllin, indicating that the effect of A23187 was caused by an increase in the intracellular cAMP level in the gland cells. From the present data it is suggested that the calcium ionophore stimulates the Cl and water secretion from frog skin gland not by a direct effect of Ca²⁺-ions per se, but in an indirect manner by stimulating the prostaglandin synthesis, which probably results in an increase in the cAMP level in the gland cells.     

Vascular prostaglandin synthesis in the spontaneously hypertensive rat.

Vascular prostaglandin synthesis was studied in tissues (aorta and inferior vena cava) obtained from spontaneously hypertensive rats (SHRs) of the Aoki-Okamoto strain and age-matched Wistar-Kyoto (WKYs) controls. PGE2 synthesis in aortas from SHRs was significantly enhanced at 10 wk of age (5.3 +/- 0.7 nmol PGE2/mg protein per 10 min vs. 1.9 +/- 0.03 nmol PGE2/mg protein per min in the WKYs, P less than 0.001) and increased progressively until 22 wk of age; PGE2alpha synthesis in SHRs was not significantly different from WKYs. In the venous walls from SHRs, PGF2alpha was the prostaglandin predominantly synthesized (7.1 +/- 0.6 vs. 1.9 +/- 0.05 nmol PGE2alpha/mg protein per 10 min in the WKY controls, P less than 0.01). The activities of 15-hydroxy prostaglandin dehydrogenase and PGE 9-ketoreductase were also compared in the two groups of animals. The only difference detected was a significant increase in venous PGE 9-ketoreductase of SHR's (7.3 +/- 0.06 vs. 4.8 +/- 0.04 nmol PGF2alpha/mg per min, P less than 0.01). The results suggest that increased vascular synthesis of prostaglandins accompanies the development of spontaneous hypertension and may serve to attenuate the effects of blood pressure elevation.     

Sodium and chloride transport by the intestine of the european flounderPlatichthys flesus adapted to fresh or sea water

1. Everted intestinal sacs prepared from Platichthys flesus adapted to sea water (SW) have higher rates of salt and water transport than did sacs prepared from fresh water adapted (FW) fish. 2. Intestines mounted in Ussing chambers gave stable open-circuit voltages and short-circuit currents after pre-incubation for 20--30 min of --1.91 +/- 0.14 (14) mV and --45.0 +/- 5.1 (14) muA/cm2, SW fish, and --1.24 +/- 0.14 (11) mV and --18.2 +/- 3.6 (11) muA/cm2, FW fish. 3. Isotope flux measurements indicated a net Na transport of 21.5 +/- 4.1 (11) neq/cm2-min in SW fish intestines, but no significant Na transport in FW fish (7.6 +/- 7.6 (9) new/cm2-min). Both preparations showed an active Cl transport, 26.6 +/- 6.1 (12) neq/cm2-min for SW and 18.5 +/- 9.7 (17) neq/cm2-min for FW fish. 4. No significant difference in the uptake of Na or Cl across the mucosa was observed between FW and SW fish. The uptake of both ions showed some saturation at high concentrations. 5. Interactions between Na and Cl uptake were small, although Cl uptake was significantly higher in Na-free solutions. 6. It is concluded that electrogenic Cl transport may be the dominant mechanism for water and salt transport in flounder intestine, and that adaptation to a saline environment involves regulation of pumping rather than Na or Cl entry across the mucosal membrane.     

In vitro primate gastric mucosa: electrical characteristics

Ion transport by the resting, isolated, rhesus gastric mucosa was assessed under conditions of minimal diffusion limitation to oxygen by 1) the substitution of Na+ and Cl- of the bathing solutions with less permeant ions, 2) the drugs amiloride and ouabain, and 3) estimation of net fluxes of 22Na by methods designed to circumvent the problem of poorly matched tissues. The mucosae developed potential differences of 51.3 +/ 3.5 mV, serosal side positive and had conductances of 5.56 +/- 0.30 mS x cm-2. The permeabilities of the tissues to D-mannitol were between 7.80 x 10(-7) and 3.15 x 10(-7) cm x s-1. The relatively high conductance of this epithelium in the absence of significant edge damage and a low (32%) paracellular conductance stems mainly from a passive permeability to Cl-; active absorption of Na+ and active secretion of Cl- contribute equally to the short-circuit current. The mucosal entry step for Na+ is amiloride sensitive, whereas the serosal exit step can be inhibited by ouabain. The entry step for Cl- at the serosal membrane is possibly sodium dependent.     

Chloride transport in glands of frog skin

The effects of beta-adrenergic stimulation on the bidirectional fluxes of Na+ and Cl- across the frog skin glands were determined. Isoproterenol elicited net serosal-to-mucosal fluxes of both Na+ (JNanet) and Cl- (JClnet) equal to 0.19 +/- 0.05 (SE) and 0.57 +/- 0.05 mueq X cm-2 X h-1, respectively. The residual current (JClnet - JNanet) of 0.38 +/- 0.05 mueq X cm-2 X h-1 closely approximates the isoproterenol-induced short-circuit current of 0.30 +/- 0.04 mueq X cm-2 X h-1. Furosemide added to the serosal side prior to isoproterenol inhibited the isoproterenol-induced net fluxes of both Na+ and Cl-. The addition of dibutyryl cAMP and 3-isobutyl-1-methylxanthine to the serosal side mimicked the action of isoproterenol by stimulating glandular short-circuit current. We conclude that an active Cl(-)-transport mechanism resides in the frog skin glands and is 1) stimulated by a beta-adrenergic agonist (its action is mimicked by cAMP) and 2) inhibited by the loop diuretic furosemide.     

Inhibition of multiplication of parainfluenza 3 virus in prostaglandin-treated WISH cells

Influence of prostaglandins E2 (PGE2) and F2alpha (PGF 2alpha) on multiplication of myxovirus parainfluenza 3 was investigated. At concentrations of 0.01--1 mug/ml prostaglandins had no direct cytotoxic effects. PGE2 and PGF2alpha inhibited multiplication of parainfluenza 3 virus at concentrations 0.1--10 mug/ml. The inhibitory effect was most pronounced when the prostaglandins were added to medium for the whole period of virus multiplication (48 hours) while little or no effect was found when prostaglandins were added before virus inoculation or for 2 hours after infection. It is suggested that prostaglandins exert an inhibitory effect on the replication phase of the virus by influencing the growth of the WISH cells.