cAMP activates the sodium pump in cultured cells of the elasmobranch rectal gland.

The inorganic ion content of rectal gland cells cultured from Squalus acanthias was studied by electron probe analysis in order to determine the effect of stimulation by cAMP. Cell sodium was reduced by 30% (P less than 0.01) at 8 min after exposure to dibutyryl cAMP and theophylline and remained low at 25 and 33 min. Chloride content also fell significantly with stimulation. Although cAMP may activate several transport sites, the results are consistent with a direct effect of stimulation to increase the activity of the sodium pump in shark rectal gland.

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Propionate induces cell swelling and K+ accumulation in shark rectal gland

AJP Cell Physiology ◽

10.1152/ajpcell.1989.257.2.c377 ◽

1989 ◽

Vol 257 (2) ◽

pp. C377-C384 ◽

Cited By ~ 23

Author(s):

G. M. Feldman ◽

F. N. Ziyadeh ◽

J. W. Mills ◽

G. W. Booz ◽

A. Kleinzeller

Keyword(s):

Atpase Activity ◽

Propionic Acid ◽

Exchange Process ◽

Squalus Acanthias ◽

Cell Swelling ◽

Rectal Gland ◽

Structural Elements ◽

Acid Diffusion ◽

Shark Rectal Gland ◽

Solute Accumulation

Small organic anions have been reported to induce cell solute accumulation and swelling. To investigate the mechanism of swelling, we utilized preparations of rectal gland cells from Squalus acanthias incubated in medium containing propionate. Propionate causes cells to swell by diffusing across membranes in its nonionic form, acidifying cell contents, and activating the Na+-H+ antiporter. The Na+-H+ exchange process tends to correct intracellular pH (pHi), and thus it maintains a favorable gradient for propionic acid diffusion and allows propionate to accumulate. Activation of the Na+-H+ antiport also facilitates Na+ entry into the cell and Nai accumulation. At the same time Na+-K+-ATPase activity, unaffected by propionate, replaces Nai with Ki, whereas the K+ leak rate, decreased by propionate, allows Ki to accumulate. As judged by 86Rb+ efflux, the reduction in K+ leak was not due to propionate-induced cell acidification or reduction in Cli concentration. Despite inducing cell swelling, propionate did not disrupt cell structural elements and F actin distribution along cell membranes.

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Mechanism of active chloride secretion by shark rectal gland: role of Na-K-ATPase in chloride transport

AJP Renal Physiology ◽

10.1152/ajprenal.1977.233.4.f298 ◽

1977 ◽

Vol 233 (4) ◽

pp. F298-F306 ◽

Cited By ~ 24

Author(s):

P. Silva ◽

J. Stoff ◽

M. Field ◽

L. Fine ◽

J. N. Forrest ◽

...

Keyword(s):

Chloride Transport ◽

Sodium Concentration ◽

Chloride Secretion ◽

Squalus Acanthias ◽

Rectal Gland ◽

Tentative Hypothesis ◽

Shark Rectal Gland ◽

Electrochemical Equilibrium

The isolated rectal gland of Squalus acanthias was stimulated to secrete chloride against an electrical and a chemical gradient when perfused in vitro by theophylline and/or dibutyryl cyclic AMP. Chloride secretion was depressed by ouabain which inhibits Na-K-ATPase. Thiocyanate and furosemide also inhibited chloride secretion but ethoxzolamide, a carbonic anhydrase inhibitor, did not. Chloride transport was highly dependent on sodium concentration in the perfusate. The intracellular concentration of chloride averaged 70-80 meq/liter in intact glands, exceeding the level expected at electrochemical equilibrium and suggesting active transport of chloride into the cell. These features suggest a tentative hypothesis for chloride secretion by the rectal gland in which the uphill transport of chloride into the cytoplasm is coupled through a membrane carrier to the downhill movement of sodium along its electrochemical gradient. The latter is maintained by the Na-K-ATPase pump while chloride is extruded into the duct by electrical forces.

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AMP-activated protein kinase and adenosine are both metabolic modulators that regulate chloride secretion in the shark rectal gland (Squalus acanthias)

AJP Cell Physiology ◽

10.1152/ajpcell.00171.2017 ◽

2018 ◽

Vol 314 (4) ◽

pp. C473-C482

Author(s):

Rugina I. Neuman ◽

Juliette A. M. van Kalmthout ◽

Daniel J. Pfau ◽

Dhariyat M. Menendez ◽

Lawrence H. Young ◽

...

Keyword(s):

Feedback Inhibition ◽

Short Circuit ◽

Short Circuit Current ◽

Chloride Secretion ◽

Squalus Acanthias ◽

Catalytic Subunit ◽

Rectal Gland ◽

Apical Side ◽

Shark Rectal Gland ◽

Amp Activated Protein Kinase

The production of endogenous adenosine during secretagogue stimulation of CFTR leads to feedback inhibition limiting further chloride secretion in the rectal gland of the dogfish shark (Squalus acanthias). In the present study, we examined the role of AMP-kinase (AMPK) as an energy sensor also modulating chloride secretion through CFTR. We found that glands perfused with forskolin and isobutylmethylxanthine (F + I), potent stimulators of chloride secretion in this ancient model, caused significant phosphorylation of the catalytic subunit Thr172 of AMPK. These findings indicate that AMPK is activated during energy-requiring stimulated chloride secretion. In molecular studies, we confirmed that the activating Thr172 site is indeed present in the α-catalytic subunit of AMPK in this ancient gland, which reveals striking homology to AMPKα subunits sequenced in other vertebrates. When perfused rectal glands stimulated with F + I were subjected to severe hypoxic stress or perfused with pharmacologic inhibitors of metabolism (FCCP or oligomycin), phosphorylation of AMPK Thr172 was further increased and chloride secretion was dramatically diminished. The pharmacologic activation of AMPK with AICAR-inhibited chloride secretion, as measured by short-circuit current, when applied to the apical side of shark rectal gland monolayers in primary culture. These results indicate that that activated AMPK, similar to adenosine, transmits an inhibitory signal from metabolism, that limits chloride secretion in the shark rectal gland.

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Mode of activation of salt secretion by C-type natriuretic peptide in the shark rectal gland

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1999.277.6.r1725 ◽

1999 ◽

Vol 277 (6) ◽

pp. R1725-R1732 ◽

Cited By ~ 8

Author(s):

Patricio Silva ◽

Richard J. Solomon ◽

Franklin H. Epstein

Keyword(s):

Short Circuit ◽

Short Circuit Current ◽

Chloride Secretion ◽

Squalus Acanthias ◽

Rectal Gland ◽

Stimulatory Action ◽

Kinase C ◽

Shark Rectal Gland ◽

Pkc Activation ◽

Stimulation Of

We studied the modes of activation of the salt-secreting rectal gland of the spiny dogfish, Squalus acanthias, by the native cardiac peptide CNP. The stimulatory action of CNP in isolated perfused glands is inhibited by 10 mM procaine, presumably by blocking release of vasoactive intestinal peptide (VIP) from nerves. Procaine reduces the slope of the dose-response curve of human CNP and that of shark CNP (each P < 0.0001). CNP increases short-circuit current in cultured rectal gland cells from 4.8 ± 1.6 to 27.0 ± 7.8 μA/cm2. It also stimulates the secretion of chloride in isolated perfused glands in the presence of 10 mM procaine from 72 ± 31 to 652 ± 173 μeq ⋅ h−1 ⋅ g−1. These results suggest that CNP has a direct cellular action not mediated by the neural release of VIP. The residual stimulation of perfused glands in the presence of procaine was almost completely inhibited by staurosporine [10 nM; an inhibitor of protein kinase C (PKC)] from 652 ± 173 to 237 ± 61 μeq ⋅ h−1 ⋅ g−1. Although CNP stimulates guanylyl cyclase in shark rectal gland, chloride secretion of perfused glands was not elicited by 8-bromoadenosine-cGMP (8-BrcGMP) alone nor by the activator of PKC phorbol ester. The combination of PKC activation and 8-BrcGMP infusion, however, stimulated chloride secretion in perfused glands from 94 ± 30 to 506 ± 61 μeq ⋅ h−1 ⋅ g−1, a level comparable to that observed in glands blocked with procaine. Several parallel pathways appear to be synergistic in activating chloride secretion stimulated by CNP in the rectal gland.

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Resolution of apical from basolateral membrane of shark rectal gland

AJP Cell Physiology ◽

10.1152/ajpcell.1986.251.5.c721 ◽

1986 ◽

Vol 251 (5) ◽

pp. C721-C726 ◽

Cited By ~ 12

Author(s):

W. P. Dubinsky ◽

L. B. Monti

Keyword(s):

Membrane Fraction ◽

Sucrose Gradient ◽

Apical Membrane ◽

Specific Activity ◽

Basolateral Membrane ◽

Anion Transport ◽

Squalus Acanthias ◽

Rectal Gland ◽

Crude Homogenate ◽

Shark Rectal Gland

Membrane fractions were isolated from the rectal gland of Squalus acanthias using differential centrifugation and a sucrose gradient run in the presence of 1 M KBr. Using the basolateral membrane marker Na+-K+-ATPase, we obtained a sixfold purification with the most highly purified fraction from the gradient (sp act = 336 +/- 37 mumol X mg protein-1 X h-1). Electrogenic Br- transport was used as a marker activity of the apical membrane, which enabled the identification and purification of a membrane fraction that is highly resolved from the basolateral membrane. The most active fraction was purified approximately 50-fold compared with the crude homogenate. In this fraction, the specific activity of electrogenic anion transport was 296 +/- 87 nmol X mg protein-1 X min-1, whereas the ATPase was only 17.6 +/- 5.7 mumol X mg protein-1 X h-1, representing about a 4-5% contamination of the apical fraction with the basolateral membrane.

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