Biomedical subjects

G A Gerencser

Publications and source records attributed to G A Gerencser.

At least 19 recordsLinked to original sources

PubMed2001

Phosphorylation of chloride-ATPase reconstituted from Aplysia gut.

The present study was primarily done to compare cation-ATPase phosphorylation kinetics with an anion-ATPase's phosphorylation kinetics because of the paucity of information in this area. Utilizing a proteolipsomal preparation containing Cl(-)-ATPase from Aplysia gut, it was demonstrated that phosphorylation of this P-type ATPase was absolutely dependent upon Mg(2+). In organic phosphate concentrations directly (P(i)) enhanced phosphoprotein formation in the presence of increasing concentrations of Mg(2+). It was also shown that the calculated rate constant for E(1)-P formation was 26/sec. This approximated E(1)-P rate constant values for other electrogenic, uniport P-type ATPases, and therefore it was concluded from the results that the anion-ATPase phosphorylation kinetics did not greatly differ from cation-ATPase phosphorylation kinetics.

Adenosine Triphosphatases↗

PubMed2001

Cl(-)-ATPases: Novel primary active transporters in biology.

Five widely documented mechanisms of chloride transport across plasma membranes are anion-coupled antiport, sodium and hydrogen-coupled symport, Cl(-)channels, and an electrochemical coupling process. No genetic evidence has yet been provided for primary active chloride transport despite numerous reports of cellular Cl(-)-stimulated ATPases co-existing, in the same tissue, with uphill chloride transport that could not be accounted for by the five common chloride transport processes. Cl(-)-stimulated ATPase activity is a common property of practically all biological cells with the major location being of mitochondrial origin. It also appears that plasma membranes are sites of Cl(-)-stimulated ATPase activity. Recent studies of Cl(-)-stimulated ATPase activity and active chloride transport in the same membrane system, including liposomes, suggest a medication by the ATPase in net movement of chloride up its electrochemical gradient across plasma membranes. Further studies, especially from a molecular biological perspective, are required to confirm a direct transport role to plasma membrane-localized Cl(-)-stimulated ATPases. J. Exp. Zool. 289:215-223, 2001.

Adenosine Triphosphatases↗

PubMed2001

Sulfate transport mechanisms in epithelial systems.

A novel invertebrate gastrointestinal transport mechanism has been shown to couple chloride-sulfate exchange in an electrogenic fashion. In the lobster, Homarus americanus, the hepatopancreas, or digestive gland, exists as an outpocketing of the digestive tract, representing a single cell layer separating the gut lumen and an open circulatory system composed of hemolymph. Investigations utilizing independently prepared brush border and basolateral membrane vesicles revealed discrete antiport systems which possess the capacity to bring about a transcellular secretion of sulfate. The luminal antiport system functions as a high-affinity, one-to-one chloride-sulfate exchanger that is stimulated by an increase in luminal hydrogen ion concentration. Such a system would take advantage of the high chloride concentration of ingested seawater as well as the high proton concentrations generated during digestion, which further suggests a potential regulation by resident sodium-proton exchangers. Exchange of one chloride for one divalent sulfate ion provides the driving force for electrogenic vectorial translocation. The basolateral antiport system was found to be electroneutral in nature, responsive to gradients of the dicarboxylic anion oxalate while lacking in proton stimulation. No evidence of sodium-sulfate co-transport, commonly reported for the brush border of vertebrate renal and intestinal epithelia, was observed in either membrane preparation. The two antiporters together can account for the low hemolymph to seawater sulfate levels previously described in decapod crustaceans. A secretory pathway for sulfate based upon electrogenic chloride-antiport may appear among invertebrates partly in response to digestion taking place in a seawater environment. J. Exp. Zool. 289:245-253, 2001.

Animals↗

PubMed2001

Effect of Laticauda semifasciata (sea snake) venom on chloride transport across the frog skin.

Addition of Laticauda semifasciata venom to the outside bathing solution of isolated frog skin elicited sustained increases in transepithelial potential difference, short-circuit current and transepithelial electrical resistance. The Laticauda semifasciata venom-induced short-circuit is carried by a net active Na+ transfer from the outside to the inside bathing solution while the increase in transepithelial resistance is accounted for by a decrease in the outside to inside Cl- flux.

Animals↗

PubMed2001

Cl(-)-ATPases: biological active transporters.

Five widely documented mechanisms of chloride transport across plasma membranes are: anion-coupled antiport; sodium and hydrogen-coupled symport; Cl- channels; and an electrochemical coupling process. No genetic evidence has yet been provided for primary active chloride transport despite numerous reports of cellular Cl(-)-stimulated ATPases co-existing, in the same tissue, with uphill chloride transport that could not be accounted for by the five common chloride transport processes. Cl(-)-stimulated ATPase activity is a common property of practically all biological cells with the major location being of mitochondrial origin. It also appears that plasma membranes are sites of Cl(-)-stimulated ATPase activity. Recent studies of Cl(-)-stimulated ATPase activity and active chloride transport in the same membrane system, including liposomes, suggest a mediation by the ATPase in net movement of chloride up its electrochemical gradient across plasma membranes. Further studies, especially from a molecular biological perspective, are required to confirm a direct transport role to plasma membrane-localized Cl(-)-stimulated ATPases.

Adenosine Triphosphatases↗

PubMed2001

The Aplysia californica Cl- pump is a P-type ATPase: evidence through inhibition studies.

Utilizing a proteoliposomal preparation containing Cl(-)-ATPase from Aplysia californica foregut, it was shown that orthovanodate inhibited Cl(-)-ATPase activity, ATP-dependent Cl- transport, ATP-dependent membrane potential change and ATP-dependent phosphorylation. N-ethylmalemide and p-chloromercurobenzoate also inhibited the Cl- pump biochemical and physiological transport characteristics. However, bafilomycin, azide, N, N'-dicyclohexylcarboiimide (DCCD), and efrapeptin had no effect on the Cl- pump biochemical or physiological characteristics, suggesting that this Cl- pump was a P-type ATPase. It was concluded that this P-type ATPase Cl- pump is the mechanism that is responsible for the net absorptive flux of Cl- in the A. californica foregut.

4-Chloromercuribenzenesulfonate↗

PubMed2001

Transport energetics of the Na+ pump in Aplysia californica gut.

Basolateral membranes of Aplysia californica foregut epithelia contain an ATP-dependent Na+ transporter (Na+ pump). Increased activity of the Na+ pump, coupled to luminal Na+/AIB symporter activity and basolateral membrane depolarization, changed the Na+ transport energetics across the basolateral membrane to a greater extent than the change in Na+ transport energetics across the luminal membrane.

Aminoisobutyric Acids↗

PubMed2000

Aplysia gut epithelial cells: luminal membrane chloride channel activity.

The Cl(-) energy gradient across the luminal membrane of Aplysia foregut epithelial cells is directed downhill from the lumen to the cellular cytosol. No primary or secondary active transporters had been shown to be involved in Cl(-) translocation across the luminal membrane. Cl(-) channel blockers impeded the movement of Cl(-) from the lumen into the foregut cellular cytosol. It was concluded that the primary means of Cl(-) transport across the luminal membrane was via Cl(-) conductance.

Animals↗

PubMed2000

Chloride transport by lobster hepatopancreas is facilitated by several anion antiport mechanisms.

Three anion antiporters have previously been demonstrated in lobster hepatopancreatic basolateral membrane vesicles (BLMV) to perform vital physiological functions in the crustacean. Cl(-) was shown to be transported by all three of the documented antiporters. The stilbene, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, also known as SITS, strongly inhibited Cl(-)/SO(4)(2-), Cl(-)/oxalate(2-) and Cl(-)/HCO(3)(-) exchange. It was concluded that Cl(-) could be transported by different modes of the documented existing anion antiporters in the lobster hepatopancreatic BLMV.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗

PubMed2000

The oxalate/sulfate antiporter in lobster hepatopancreas: internal and external binding constants.

Utilizing a purified basolateral plasma membrane vesicle (BLMV) preparation containing a sulfate/oxalate antiporter, it was demonstrated that sulfate exhibited similar binding characteristics to the transporter whether bound internally or externally. It was also demonstrated that oxalate had similar binding characteristics to the antiporter whether it was bound internally or externally. Oxalate had a greater affinity to the transporter than did sulfate. Several organic anions affected binding and, therefore, overall transport by the antiporter. Most notably, sulfate was the only anion that stimulated oxalate uptake into BLMVs, which suggests a conservative binding specificity for the antiporter. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and/or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) inhibited the transport rate, confirming the existence of oxalate/sulfate exchange by the transporter. These results suggest that oxalate, not sulfate, regulates the transport rate because of its greater affinity to the transporter.

Animals↗

PubMed1999

Chloride transport in the ferret trachea.

A net secretion of chloride stimulated by carbamylcholine was observed in whole trachea. Luminal anthracene-9-carboxylic acid inhibited the net secretion of chloride and the transepithelial potential difference across the isolated trachea. Submucosal ouabain inhibited the net secretion of chloride and submucosal ouabain, or submucosal bumetanide inhibited the transepithelial potential difference across the isolated trachea. Short-circuited flat sheets of trachea manifested a net secretion of chloride induced by carbamylcholine. Serosal ouabain inhibited the short-circuit current and net chloride flux across isolated flat sheets of trachea.

Animals↗

PubMed1998

Intracellular K+ activities in Aplysia gut: effects of transport inhibitors on the Na+ pump.

Na+ absorption by the Aplysia californica foregut is affected through an active Na+ transport mechanism located in the basolateral membrane of the epithelial absorptive cells. Since Cl- absorption by the Aplysia gut has been shown to be very different from that demonstrated in vertebrate gut, the present study was undertaken to discern if Na+ transport was also different from that observed in vertebrate preparations. Utilizing microelectrode technique, it was demonstrated that intracellular K+ activity is above electrochemical equilibrium in the Aplysia absorptive cells and that serosal ouabain, Ba2+ or Cd2+ abolished this asymmetry in K+ electrochemical potential. Neither bumetanide nor furosemide had any effect on intracellular K+ activities, mucosal membrane potentials or transepithelial potentials in the Aplysia gut preparation. These results are consistent with the operation of a basolateral Na+/K+ pump.

Animals↗

PubMed1997

Transport energetics of the Cl- pump in Aplysia gut.

Basolateral membranes of Aplysia foregut epithelia contain an ATP-dependent Cl- transporter (Cl- pump). Increased activity of the Cl- pump, coupled to apical and basolateral membrane depolarization, changed the Cl- transport energetics across the apical membrane but did not change the vectorially-opposite Cl- transport energetics across the basolateral membrane.

Aminoisobutyric Acids↗

PubMed1996

An electrogenic chloride pump in a zoological membrane.

Two widely documented mechanisms of chloride transport across animal plasma membranes are anion-coupled antiport and sodium-coupled symport. No direct genetic evidence has yet been provided for primary active chloride transport despite numerous reports of cellular CI(-)-stimulated ATPases coexisting, in the same tissue, with uphill chloride transport that could not be accounted for by the two common chloride transport processes. CI(-)-stimulated ATPases are a common property of practically all animal cells, with the major location being of mitochondrial origin. It also appears that the plasma membranes of animal cells are sites of CI(-)-stimulated ATPase activity. Recent studies of CI(-)-stimulated ATPase activity and chloride transport in the same membrane system, including liposomes, suggest a mediation by the ATPase in net movement of chloride up its electrochemical gradient across animal plasma membranes. Further studies, especially from a molecular biological perspective, are required to confirm a direct transport role to plasma membrane-localized Cl(-)-stimulated ATPases.

Adenosine Triphosphatases↗

PubMed1996

Antiport-driven sulfate secretion in an invertebrate epithelium.

A novel invertebrate gastrointestinal transport mechanism has been shown to couple chloride/sulfate exchange in an electrogenic fashion. In the lobster, Homarus americanus, the hepatopancreas, or digestive gland, exists as an outpocketing of the digestive tract, representing a single cell layer separating the gut lumen and an open circulatory system comprised of hemolymph. Investigations utilizing independently prepared brush-border and basolateral membrane vesicles revealed discrete antiport systems which possess the capacity to bring about a transcellular secretion of sulfate. The luminal antiport system functions as a high affinity, one-to-one chloride-sulfate exchanger that is stimulated by an increase in luminal hydrogen ion concentration. Such a system would take advantage of the high chloride concentration of ingested seawater, as well as the high proton concentrations generated during digestion, which further suggests a potential regulation by resident sodium-proton exchangers. Exchange of one chloride for one divalent sulfate ion provides the driving force for electrogenic vectorial translocation. The basolateral antiport system was found to be electroneutral in nature, responsive to gradients of the dicarboxylic anion oxalate, while lacking in proton stimulation. No evidence of sodium-sulfate cotransport, commonly reported for the brush border of vertebrate renal and intestinal epithelia, was observed in either membrane preparation. The two antiporters together can account for the low hemolymph to seawater sulfate levels previously described in decapod crustaceans. A secretory pathway for sulfate based upon electrogenic chloride-antiport may appear among invertebrates partly in response to digestion taking place in a seawater environment.

Animals↗

PubMed1996

Reconstituted Cl- pump protein: a novel ion(Cl-)-motive ATPase.

Cl- absorption by the Aplysia californica foregut is effected through an active Cl- transport mechanism located in the basolateral membrane of the epithelial absorptive cells. These basolateral membranes contain both Cl(-)-stimulated ATPase and ATP-dependent Cl- transport activities which can be incorporated into liposomes via reconstitution. Utilizing the proteoliposomal preparation, it was demonstrated that ATP, and its subsequent hydrolysis, Mg2+, Cl-, and a pH optimum of 7.8 were required to generate maximal intraliposomal Cl- accumulation, electrical negativity, and ATPase activity. Additionally, an inwardly-directed valinomycin-induced K+ diffusion potential, making the liposome interior electrically positive, enhanced both ATP-driven Cl- accumulation and electrical potential while an outwardly-directed valinomycin-induced K+ diffusion potential, making the liposome interior electrically negative, decreased both ATP-driven Cl- accumulation and electrical potential compared with proteoliposomes lacking the ionophore. Either orthovanadate or p-chloromercurobenzene sulfonate inhibited both the ATP-dependent intraliposomal Cl- accumulation, intraliposomal negative potential difference, and also Cl(-)-stimulated ATPase activity. Both aspects of Cl- pump transport kinetics and its associated catalytic component kinetics were the first obtained utilizing a reconstituted transporter protein. These results strongly support the hypothesis that Cl(-)-ATPase actively transports Cl- by an electrogenic process.

Adenosine Triphosphatases↗

PubMed1996

Glutathione inhibition of silver-enhanced sodium transport across toad skin.

Silver stimulated short-circuit current and transepithelial potential difference. Glutathione inhibited the silver-induced short-circuit current. There was a dose-response inhibition of silver-induced short-circuit current by glutathione. The silver-induced short-circuit current is carried by a net active sodium transfer from the outside to the inside bathing solution.

Animals↗

PubMed1996

The chloride pump: a Cl(-)-translocating P-type ATPase.

Three widely documented mechanisms of chloride transport across plasma membranes are anion-coupled antiport, sodium-coupled symport, and an electrochemical coupling process. No direct genetic evidence has yet been provided for primary active chloride transport despite numerous reports of cellular Cl(-)-stimulated adenosine triphosphate (ATP)ases coexisting in the same tissue with uphill chloride transport that could not be accounted for by the three common chloride transport processes. Cl(-)-stimulated ATPases are a common property of practically all biological cells, with the major location being of mitochondrial origin. It also appears that plasma membranes are sites of Cl(-)-stimulated ATPase activity. Recent studies of Cl(-)-stimulated ATPase activity and chloride transport in the same membrane system, including liposomes, suggest a mediation by the ATPase in net movement of chloride up its electrochemical gradient across plasma membranes. Further studies, especially from a molecular biological perspective, are required to confirm a direct transport role to plasma membrane-localized Cl(-)-stimulated ATPases.

Adenosine Triphosphatases↗