THE EFFECTS OF MAGNESIUM ON NUCLEOSIDE PHOSPHATASE ACTIVITY IN FROG SKIN

Histochemical tests, employing the Wachstein-Meisel medium, indicate that nucleoside triphosphatase activity is found predominantly in two areas of the frog skin epidermis: (1) in mitochondria, where activity is enhanced by dinitrophenol, Mg2+ dependent, but inhibited by fixation; and (2) apparently associated with cell membranes of the middle and outer portions of the epidermis, where activity is inhibited by Mg2+, unaffected by dinitrophenol, and only slightly reduced by fixation. Spectrophotometric analysis shows that Mg2+ in the medium does not increase spontaneous hydrolysis of ATP, thus obviating the possible explanation that changes in substrate concentrations in the medium lead to alterations in the "staining" distributions. It is postulated that perhaps the two enzymes differ in their requirements for substrate—one requiring the polyphosphate to be in complexed form with Mg2+, the other uncomplexed. Concentrations of Mg2+ required to inhibit cell membrane nucleoside triphosphatase activity also inhibit the electrical potential difference and short-circuit current of the frog skin. Although these observations might be taken as presumptive evidence of the cell membrane enzyme as a component of the ion pump system, because of certain dissimilarities with respect to the biochemists' "transport ATPase" and for other reasons discussed in the paper, any definite conclusions in this regard are premature.

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Effect of furosemide on the electrical parameters of frog skin

AJP Renal Physiology ◽

10.1152/ajprenal.1982.243.6.f581 ◽

1982 ◽

Vol 243 (6) ◽

pp. F581-F587 ◽

Cited By ~ 1

Author(s):

A. Corcia ◽

S. R. Caplan

Keyword(s):

Active Transport ◽

Frog Skin ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Relative Increase ◽

Electrical Potential Difference ◽

Electrical Parameters ◽

Active Conductance ◽

Solution Bathing

When added to the mucosal solution bathing isolated frog skin at concentrations ranging from 5 X 10(-4) to 3 X 10(-3) M, the diuretic furosemide increased both the active transport of sodium and the electrical potential difference across the tissue in a dose-dependent way. The same effect was observed in chloride-free solutions. Mucosal furosemide also decreased the passive unidirectional fluxes of chloride. We believe that as far as electrical parameters are concerned mucosal furosemide has a double effect in frog skin: it increases the active conductance to sodium across the mucosal membrane, thus increasing active transport, and decreases the passive permeability to chloride, thus altering the passive conductance of the skin. The relative increase in short-circuit current was, however, invariably greater than the increase of the active conductance, suggesting the influence of yet a third effect. The effect of mucosal furosemide on active sodium transport was blocked by amiloride (5 X 1-(-5) M) and was independent of vasopressin. Qualitatively the effect was similar to the effect produced by triphenylmethylphosphonium ion.

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Energetics of Sodium Transport in Frog Skin

The Journal of General Physiology ◽

10.1085/jgp.59.1.77 ◽

1972 ◽

Vol 59 (1) ◽

pp. 77-91 ◽

Cited By ~ 44

Author(s):

F. L. Vieira ◽

S. R. Caplan ◽

A. Essig

Keyword(s):

Free Energy ◽

Oxygen Consumption ◽

Sodium Transport ◽

Frog Skin ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Electrical Potential Difference ◽

Rate Of Oxygen Consumption ◽

Phenomenological Coefficients

Studies were made of the dependence of the rate of oxygen consumption, Jr, on the electrical potential difference, Δψ, across the frog skin. After the abolition of sodium transport by ouabain the basal oxygen consumption was independent of Δψ. In fresh skins Jr was a linear function of Δψ over a range of at least ±70 mv. Treatment with aldosterone stimulated the short-circuit current, Io, and the associated rate of oxygen consumption, Jro, and increased their stability; linearity was then demonstrable over a range of ±160 mv. Brief perturbations of Δψ (±30–200 mv) did not alter subsequent values of Io. Perturbations for 10 min or more produced a "memory" effect both with and without aldosterone: accelerating sodium transport by negative clamping lowered the subsequent value of Io; positive clamping induced the opposite effect. Changes in Jro were more readily detectable in the presence of aldosterone; these were in the same direction as the changes in Io. The linearity of Jr in Δψ indicates the validity of analysis in terms of linear nonequilibrium thermodynamics—brief perturbations of Δψ appear to produce no significant effect on either the phenomenological coefficients or the free energy of the metabolic driving reaction. Hence it is possible to evaluate this free energy.

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OSMOTIC INHIBITION OF THE NATRIFERIC RESPONSE OF THE TOAD URINARY BLADDER TO VASOPRESSIN

Journal of Endocrinology ◽

10.1677/joe.0.0670119 ◽

1975 ◽

Vol 67 (1) ◽

pp. 119-125

Author(s):

P. J. BENTLEY

Keyword(s):

Urinary Bladder ◽

Water Movement ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Toad Bladder ◽

Toad Urinary Bladder ◽

Electrical Potential Difference ◽

Osmotic Gradient

SUMMARY The electrical potential difference and short-circuit current (scc, reflecting active transmural sodium transport) across the toad urinary bladder in vitro was unaffected by the presence of hypo-osmotic solutions bathing the mucosal (urinary) surface, providing that the transmural flow of water was small. Vasopressin increased the scc across the toad bladder (the natriferic response), but this stimulation was considerably reduced in the presence of a hypo-osmotic solution on the mucosal side, conditions under which water transfer across the membrane was also increased. This inhibition of the natriferic response did not depend on the direction of the water movement, for if the osmotic gradient was the opposite way to that which normally occurs, the response to vasopressin was still reduced. The natriferic response to cyclic AMP was also inhibited in the presence of an osmotic gradient. Aldosterone increased the scc and Na+ transport across the toad bladder but this response was not changed when an osmotic gradient was present. The physiological implications of these observations and the possible mechanisms involved are discussed.

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Active electrolyte transport in mammalian buccal mucosa

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1988.255.3.g286 ◽

1988 ◽

Vol 255 (3) ◽

pp. G286-G291 ◽

Cited By ~ 3

Author(s):

R. C. Orlando ◽

N. A. Tobey ◽

V. J. Schreiner ◽

R. D. Readling

Keyword(s):

Buccal Mucosa ◽

Short Circuit ◽

Basolateral Membrane ◽

Electrical Potential ◽

Short Circuit Current ◽

Electrolyte Transport ◽

Electrical Potential Difference ◽

Ussing Chambers ◽

Net Fluxes

The transmural electrical potential difference (PD) was measured in vivo across the buccal mucosa of humans and experimental animals. Mean PD was -31 +/- 2 mV in humans, -34 +/- 2 mV in dogs, -39 +/- 2 mV in rabbits, and -18 +/- 1 mV in hamsters. The mechanisms responsible for this PD were explored in Ussing chambers using dog buccal mucosa. After equilibration, mean PD was -16 +/- 2 mV, short-circuit current (Isc) was 15 +/- 1 microA/cm2, and resistance was 1,090 +/- 100 omega.cm2, the latter indicating an electrically "tight" tissue. Fluxes of [14C]mannitol, a marker of paracellular permeability, varied directly with tissue conductance. The net fluxes of 22Na and 36Cl were +0.21 +/- 0.05 and -0.04 +/- 0.02 mueq/h.cm2, respectively, but only the Na+ flux differed significantly from zero. Isc was reduced by luminal amiloride, serosal ouabain, or by reducing luminal Na+ below 20 mM. This indicated that the Isc was determined primarily by active Na+ absorption and that Na+ traverses the apical membrane at least partly through amiloride-sensitive channels and exits across the basolateral membrane through Na+-K+-ATPase activity. We conclude that buccal mucosa is capable of active electrolyte transport and that this capacity contributes to generation of the buccal PD in vivo.

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Effect of calcium on ion transport and electrical properties of tracheal epithelium

Journal of Applied Physiology ◽

10.1152/jappl.1978.44.6.900 ◽

1978 ◽

Vol 44 (6) ◽

pp. 900-904 ◽

Cited By ~ 11

Author(s):

M. G. Marin ◽

M. M. Zaremba

Keyword(s):

Electrical Properties ◽

Ion Transport ◽

Calcium Concentration ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Tracheal Epithelium ◽

Electrical Potential Difference ◽

Tracheal Lumen

Active transport of Cl- toward the tracheal lumen and Na+ away from the lumen creates an electrical potential difference across dog tracheal epithelium. This study examined in vitro the effect of varying calcium concentration in the bathing media on the ion transport and electrical properties of dog tracheal epithelium. In six pairs of epithelia, changing calcium concentration from 1.9 to 0 mM resulted in a significant decrease in electrical resistance, from 318 +/- 36 to 214 +/- 24 omega.cm2. Short-circuit current and net Cl- and Na+ fluxes measured under short-circuit conditions were not changed significantly. Changing calcium concentration from 1.9 to 10 mM resulted in no significant change from control in the electrical properties nor in net Cl- and Na+ fluxes (short-circuit conditions). Histamine (10(-4) M) produced a significantly smaller increase in short-circuit current in 0 than in 1.9 mM Ca2+ (+5 +/- 2 vs. +12 +/- 2 microamperemeter/cm2). However, electrical changes were not significantly different in 1 or 10 mM Ca2+. These results indicate that calcium lack increased permeability of tracheal epithelium and that the increase in short-circuit current due to histamine depended in part on calcium.

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Effect of acetazolamide on sodium and chloride transport by in vitro rabbit ileum

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1975.228.6.1808 ◽

1975 ◽

Vol 228 (6) ◽

pp. 1808-1814 ◽

Cited By ~ 40

Author(s):

HN Nellans ◽

RA Frizzell ◽

SG Schultz

Keyword(s):

Cyclic Amp ◽

Chloride Transport ◽

Short Circuit ◽

Electrical Potential ◽

Direct Interaction ◽

Short Circuit Current ◽

Electrical Potential Difference ◽

Membrane Component ◽

Rabbit Ileum

Acetazolamide (8 mM) aboishes active Cl absorption and inhibits but does not abolish active Na absorption by stripped, short-circuited rabbit ileum. These effects are not accompanied by significant changes in the transmural electrical potential difference or short-circuit current. Studies of the undirectional influxes of Na andCl indicate that acetazolamide inhibits the neutral, coupled NaCl influx process at the mucosal membranes. This action appears to explain the observed effect of acetazolamide on active, transepithelial Na and Cl transport. Acetazolamide did not significantly inhibit either spontaneous or theophylline-induced Cl secretion by this preparation, suggesting that the theophylline-induced secretion may not simply be due tothe unmasking of a preexisting efflux process when the neutral influx mechanism is inhibited by theophylline. Finally, inhibition of the neutral NaCl influx process by acetazolamide does not appear to be attributable to an inhibition of endogenous HCO3production or an elevation in intracellular cyclic-AMP levels. Instead, it appearstheat the effect of acetazolamide is due to a direct interaction with a membrane component involved in the coupled influx process.

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INTERRELATIONSHIP OF THE EFFECTS OF ALDOSTERONE AND THYROID HORMONES ON SODIUM TRANSPORT AND ELECTRICAL PROPERTIES OF RAT COLON

Journal of Endocrinology ◽

10.1677/joe.0.0480189 ◽

1970 ◽

Vol 48 (2) ◽

pp. 189-197 ◽

Cited By ~ 12

Author(s):

C. J. EDMONDS ◽

B. D. THOMPSON ◽

JANE MARRIOTT

Keyword(s):

Body Weight ◽

Electrical Resistance ◽

Actinomycin D ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Rat Colon ◽

Electrical Potential Difference ◽

Influx Rate ◽

Descending Colon

SUMMARY Transmucosal electrical potential difference (p.d.), short-circuit current, electrical resistance and Na+ influx rate of the descending colon were similar in euthyroid and hypothyroid rats, the latter having been treated earlier with an ablation dose of 131I. However, in contrast to the considerable p.d. increase found in normal rats, little change of p.d. was found in hypothyroid rats when they were Na+ depleted or given an intravenous aldosterone infusion. A single small dose of tri-iodothyronine (T3) (1 μg/100g body weight) or a larger dose of thyroxine given to hypothyroid rats 10–16 h before aldosterone, restored the p.d. response to normal, although these doses did not influence the animal's oxygen consumption. Fasting for 3 days or giving actinomycin D (8 μg/100 g body weight) abolished the effect of T3 but this did not influence the action of aldosterone in euthyroid animals.

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An Investigation of the Role of Possible Neural Mechanisms in Cholera Toxin-Induced Secretion in Rabbit Ileal Mucosa in Vitro

Clinical Science ◽

10.1042/cs0770161 ◽

1989 ◽

Vol 77 (2) ◽

pp. 161-166 ◽

Cited By ~ 4

Author(s):

K. J. Moriarty ◽

N. B. Higgs ◽

M. Woodford ◽

L. A. Turnberg

Keyword(s):

Cholera Toxin ◽

Fluid Transport ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Electrical Potential Difference ◽

Rabbit Ileum ◽

Ileal Mucosa

1. Cholera toxin stimulates intestinal secretion in vitro by activation of mucosal adenylate cyclase. However, it has been proposed that cholera toxin promotes secretion in vivo mainly through an indirect mechanism involving enteric neural reflexes. 2. We examined this hypothesis further by studying the influence of neuronal blockade on cholera toxin-induced changes in fluid transport across rabbit ileum in vitro. Mucosa, stripped of muscle layers, was mounted in flux chambers and luminal application of crude cholera toxin (2 μg/ml) caused a delayed but sustained rise in the short-circuit current, electrical potential difference and Cl− secretion. Pretreatment with the nerve-blocking drug, tetrodotoxin (5 × 10−6 mol/l serosal side), failed to influence the secretory response to cholera toxin, and addition of tetrodotoxin at the peak response to cholera toxin also had no effect. 3. That tetrodotoxin could block neurally mediated secretagogues was confirmed by the demonstration that the electrical responses to neurotensin (10−7 mol/l and 10−8 mol/l) were blocked by tetrodotoxin (5 × 10−6 mol/l). Furthermore, the response to cholera toxin of segments of ileum, which included the myenteric, submucosal and mucosal nerve plexuses, was not inhibited by tetrodotoxin. 4. We conclude that cholera toxin-induced secretion in rabbit ileum in vitro is not mediated via a neurological mechanism.

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In vitro studies of sodium transport across the lower intestine of a desert parrot

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1980.239.3.r285 ◽

1980 ◽

Vol 239 (3) ◽

pp. R285-R290

Author(s):

E. Skadhauge ◽

T. J. Dawson

Keyword(s):

Short Circuit ◽

Electrical Potential ◽

Flux Ratio ◽

Short Circuit Current ◽

Electrical Potential Difference ◽

Na Transport ◽

Salt Loading ◽

Ussing Chambers ◽

Lower Intestine

The lower intestine (coprodeum and colon) of the Australian parrot, the galah, was mounted in Ussing chambers. Short-circuit current (SCC), electrical potential difference (PD), and unidirectional fluxes of Na and Cl were measured in birds that were fed mixed seeds or were NaCl loaded. The net Na transport of both coprodeum and colon was nearly equal to the SCC, and the flux ratio for Cl was unity. In birds which received mixed seeds, average coprodeal Na transport was 7.8 mu eq . cm-2 . h-1, and PD was 19 mV. The Km for Na was 5.7 meq/l. In colon, Na transport was reduced by 67% and PD by 70%. The ratio between unidirectional Na and Cl fluxes in the serosa-mucosa direction was 0.7. Salt loading suppressed coprodeal, but increased colonic Na transport. The coprodeal and colonic SCC and NA transport of birds receiving mixed seeds were inhibited by amiloride on the mucosal side. Colonic SCC of NaCl-loaded birds was only slightly reduced by amiloride (by 17%), but stimulated by amino acids (by 18%).

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Electrical properties of the otic vesicle epithelium in the chick embryo

Development ◽

10.1242/dev.97.1.125 ◽

1986 ◽

Vol 97 (1) ◽

pp. 125-139

Author(s):

J. J. Represa ◽

E. Barbosa ◽

F. Giraldez

Keyword(s):

Electrical Properties ◽

Chick Embryo ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

High Rate ◽

Otic Vesicle ◽

Selectivity Ratio ◽

Electrical Potential Difference ◽

Leaky Epithelia

The electrophysiological properties of the epithelium of the otic vesicle were studied in the chick embryo using conventional microelectrode techniques. A preparation is described that allows continuous recording of transmural potential and resistance during changes in the composition of the bathing fluid. Vesicles in stages 18 to 22 showed a spontaneous transmural potential (ET) that ranged from 2 to 6 mV, inner positive. This electrical potential difference was abolished after 2h incubation in K+-free strophantidin (10−4M) and it increased by about twofold immediately after addition of the cation ionophore Amphotericin B (250 µM) to the bath. The specific resistance of the wall (RT) was about 80 Ωcm2 between stages 18 and 22 indicating a low-resistance, noncellular, permeation pathway for current flow. The short-circuit current, calculated from ET and RT was about 50×l0−6A cm−2 throughout this period. This corresponds to a net flux of 187×10−8 mol cm−2h−1 of a single cation pumped towards the vesicular cavity. Diffusion potentials (salt gradients and single-ion substitutions) showed a selectivity ratio PK:PNa:PCl = 1:0·9:0·7, which is that of a weakly charged aqueous pathway. Measurements of vesicular volume and surface area showed an increase by a factor of ten in the size of the vesicle with maximal rates of change in volume of 5µl cm−2h−1. The electrical properties reported here for the epithelium of the otic vesicle resemble very much those of ‘leaky’ epithelia which are known to transport ions and water at a very high rate.

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