Kinetic analysis of electrogenic 2 Na+-1 H+ antiport in crustacean hepatopancreas

Na+ uptake by short-circuited brush-border membrane vesicles of the hepatopancreatic epithelium from the freshwater prawn Macrobrachium rosenbergii was Cl- independent, amiloride sensitive, and stimulated by a transmembrane proton gradient ([H+]i greater than [H+]o). Na+ influx (3-s uptake) was a sigmoidal function of [Na]o (2.5-150 mM), when pHi = 6.0, pHo = 8.0, and followed the Hill equation for binding cooperativity [maximal Na+ influx (Jm) = 140.6 nmol mg-1s-1; affinity constant (K') = 82.2 mM Na+; Hill coefficient (n) = 2.07]. Influx kinetic analyses at physiological conditions suggested two external cation-binding sites shared by Na+ and H+ (proton dissociation constant Pk1 = 5.7; Pk2 = 4.0) and a single internal cation site used only by H+ (Pk = 6.5). Amiloride was a competitive inhibitor of Na+ transport at both external binding sites (Ki1 = 50 microM; Ki2 = 1,520 microM). Electrogenic Na+-H+ exchange by these vesicles was demonstrated using an equilibrium-shift method of analysis and a transmembrane electrical potential difference as the only driving force for transport. In addition, electrogenic net Na+ influx (3-s uptake) was observed in vesicles loaded with 5 mM 22Na at pH 7.0 and exposed to media containing several 22Na or proton concentrations. Results suggest the following exchange model: low [Na]o, (1 Na+ and 1 H+)-1 H+; high [Na+]o, 2 Na+-1 H+. This antiport mechanism may account for two major functional operations of the gastrointestinal tract in these animals: 1) proton secretion against considerable concentration gradients leading to stomach luminal acidification, and 2) Na+ absorption from lumen to cytoplasm potentially making a significant contribution to organismic ion balance.

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Sodium and calcium share the electrogenic 2 Na(+)-1 H+ antiporter in crustacean antennal glands

AJP Renal Physiology ◽

10.1152/ajprenal.1990.259.5.f758 ◽

1990 ◽

Vol 259 (5) ◽

pp. F758-F767

Author(s):

G. A. Ahearn ◽

P. Franco

Keyword(s):

Driving Forces ◽

Electrical Potential ◽

Membrane Vesicles ◽

Homarus Americanus ◽

Competitive Inhibitor ◽

Hill Coefficient ◽

Affinity Constant ◽

Electrical Potential Difference ◽

Static Head ◽

Transmembrane Electrical Potential

Na uptake by short-circuited epithelial brush-border membrane vesicles of Atlantic lobster (Homarus americanus) antennal gland labyrinth was Cl independent, amiloride sensitive, and stimulated by a transmembrane H+ gradient [( H]i greater than [H]o; i is internal, o is external). Na influx (2.5-s uptake) was a sigmoidal function of [Na]o (25-400 mM) when pHi = 5.0 and pHo = 8.0 and followed the Hill equation for binding cooperatively [apparent maximal influx (Jmax) = 271 nmol.mg protein-1.s-1, apparent affinity constant for Na (KNa) = 310 mM Na, and Hill coefficient (n) = 2.41]. Amiloride acted as a competitive inhibitor of Na binding to two external sites with markedly dissimilar apparent amiloride affinities (Ki1 = 14 microM; Ki2 = 1,340 mM). Electrogenic Na-H antiport by these vesicles was demonstrated by equilibrium-shift experiments in which an imposed transmembrane electrical potential difference was the only driving force for exchange. A transport stoichiometry of 2 Na to 1 H was demonstrated with the static-head technique in which a balance of driving forces was attained with 10:1 Na gradient and 100:1 H gradient. External Ca, like amiloride, was a strong competitive inhibitor of Na-H exchange, acting at two sites on the outer vesicular face with markedly different apparent divalent cation affinities (Ki1 = 20 microM; Ki2 = 500 microM). Ca-H exchange by electrogenic Na-H antiporter was demonstrated in complete absence of Na by use of an outward H gradient in presence and absence of amiloride. Both external amiloride (Ki1 = 70 microM; Ki2 = 500 microM) and Na (Ki1 = 12 mM; Ki2 = 380 mM) were competitive inhibitors of Ca-H exchange. These results suggest that the electrogenic 2 Na-1 H exchanger characterized for this crustacean epithelium may also have a role in organismic Ca balance.

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Allosteric Regulation of Bk Channel Gating by Ca2+ and Mg2+ through a Nonselective, Low Affinity Divalent Cation Site

The Journal of General Physiology ◽

10.1085/jgp.118.5.607 ◽

2001 ◽

Vol 118 (5) ◽

pp. 607-636 ◽

Cited By ~ 109

Author(s):

X. Zhang ◽

C.R. Solaro ◽

C.J. Lingle

Keyword(s):

Divalent Cation ◽

Binding Sites ◽

Time Course ◽

Cytosolic Calcium ◽

Bk Channels ◽

Bk Channel ◽

Cation Binding ◽

Cation Site ◽

Current Activation ◽

Activation Rates

The ability of membrane voltage to activate high conductance, calcium-activated (BK-type) K+ channels is enhanced by cytosolic calcium (Ca2+). Activation is sensitive to a range of [Ca2+] that spans over four orders of magnitude. Here, we examine the activation of BK channels resulting from expression of cloned mouse Slo1 α subunits at [Ca2+] and [Mg2+] up to 100 mM. The half-activation voltage (V0.5) is steeply dependent on [Ca2+] in the micromolar range, but shows a tendency towards saturation over the range of 60–300 μM Ca2+. As [Ca2+] is increased to millimolar levels, the V0.5 is strongly shifted again to more negative potentials. When channels are activated by 300 μM Ca2+, further addition of either mM Ca2+ or mM Mg2+ produces similar negative shifts in steady-state activation. Millimolar Mg2+ also produces shifts of similar magnitude in the complete absence of Ca2+. The ability of millimolar concentrations of divalent cations to shift activation is primarily correlated with a slowing of BK current deactivation. At voltages where millimolar elevations in [Ca2+] increase activation rates, addition of 10 mM Mg2+ to 0 Ca2+ produces little effect on activation time course, while markedly slowing deactivation. This suggests that Mg2+ does not participate in Ca2+-dependent steps that influence current activation rate. We conclude that millimolar Mg2+ and Ca2+ concentrations interact with low affinity, relatively nonselective divalent cation binding sites that are distinct from higher affinity, Ca2+-selective binding sites that increase current activation rates. A symmetrical model with four independent higher affinity Ca2+ binding steps, four voltage sensors, and four independent lower affinity Ca2+/Mg2+ binding steps describes well the behavior of G-V curves over a range of Ca2+ and Mg2+. The ability of a broad range of [Ca2+] to produce shifts in activation of Slo1 conductance can, therefore, be accounted for by multiple types of divalent cation binding sites.

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Effects of theophylline and cAMP on intestinal allosteric chloride transport in freshwater prawns

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1984.247.1.r196 ◽

1984 ◽

Vol 247 (1) ◽

pp. R196-R202

Author(s):

G. A. Ahearn ◽

L. K. Kullama

Keyword(s):

Divalent Cation ◽

Cyclic Nucleotide ◽

Apical Membrane ◽

Chloride Transport ◽

Macrobrachium Rosenbergii ◽

Freshwater Prawn ◽

Affinity Constant ◽

Intracellular Camp ◽

Cyclic Monophosphate ◽

Monovalent Ions

Active transmural Cl- transport across the intestine of the freshwater prawn Macrobrachium rosenbergii and the transmural potential difference resulting from the net movements of this ion and Na+ are significantly reduced or abolished in the presence of 10 mM theophylline or 1 mM dibutyryl adenosine 3',5'-cyclic monophosphate (DB-cAMP). The locus of theophylline or DB-cAMP action appears to be at the epithelial apical membrane where increased intracellular cAMP or other cyclic nucleotide such as guanosine 3',5'-cyclic monophosphate (cGMP) may interact directly or through another agent, such as the divalent cation Ca2+, to reduce or eliminate coupled Na+-Cl- influx into the cell from the gut lumen. Under control conditions, cotransport of Na+ and Cl- across the epithelial apical membrane of prawn intestine occurs by an allosteric carrier protein exhibiting sigmoidal influx kinetics for the two monovalent ions. Exogenous Ca2+ is a third binding ligand for this multisubunit protein, with the divalent cation serving as an allosteric activator of the transport system. Bilateral intestinal incubation with 10 mM theophylline abolished Cl- influx (control, 0.71 +/- 0.23; theophylline treated, 0.03 +/- 0.03 mumol X cm-2 X h-1). Addition of 1 mM DB-cAMP to intestinal incubation saline significantly (P less than 0.01) reduced the maximal Cl- influx velocity from 0.76 +/- 0.08 to 0.33 +/- 0.05 mumol X cm-2 X h-1 without altering the anion affinity constant (control, 102 +/- 5; DB-cAMP, 96 +/- 19 mM). In addition, the cyclic nucleotide had no effect on the Hill interaction coefficient of the transfer mechanism (control, 3.22 +/- 0.12; DB-cAMP, 3.42 +/- 0.68).(ABSTRACT TRUNCATED AT 250 WORDS)

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Giant freshwater prawn (Macrobrachium rosenbergii de Man, 1879) farming in brackish water areas of the Mekong Delta, Vietnam

Can Tho University Journal of Science ◽

10.22144/ctu.jen.2017.053 ◽

2017 ◽

Vol 07 ◽

pp. 82 ◽

Cited By ~ 1

Author(s):

Hai, T.N. ◽

Phuong, N.T. ◽

Huong, D.T.T. ◽

Viet, L.Q. ◽

Huong, H.K.

Keyword(s):

Brackish Water ◽

Macrobrachium Rosenbergii ◽

Mekong Delta ◽

Freshwater Prawn ◽

Giant Freshwater Prawn ◽

De Man

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Effect of various medium compositions on survival and hatching rates of embryos of the giant freshwater prawn Macrobrachium rosenbergii cultured in vitro

Fisheries Science ◽

10.1046/j.1444-2906.2001.00200.x ◽

2001 ◽

Vol 67 (1) ◽

pp. 64-70 ◽

Cited By ~ 9

Author(s):

Praneet Damrongphol ◽

Pleanphit Jaroensastraraks ◽

Boonserm Poolsanguan

Keyword(s):

Macrobrachium Rosenbergii ◽

Freshwater Prawn ◽

Giant Freshwater Prawn ◽

Hatching Rates

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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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