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H Garty

Publications and source records attributed to H Garty.

12 recordsLinked to original sources
PubMed1992

Expression of amiloride-sensitive Na+ channels of hen lower intestine in Xenopus oocytes: electrophysiological studies on the dependence of varying NaCl intake.

Epithelial Na+ channels were incorporated into the plasma membrane of Xenopus laevis oocytes after micro-injection of RNA from hen lower intestinal epithelium (colon and coprodeum). The animals were fed either a normal poultry food which contained NaCl (HS), or a similar food devoid of NaCl (LS). Oocytes were monitored for the expression of amiloride-sensitive sodium channels by measuring membrane potentials and currents. Oocytes injected with poly(A)+RNA prepared from HS animals or non-injected control oocytes showed no detectable sodium currents, whereas oocytes injected with LS-poly(A)+RNA had large amiloride-blockable sodium currents. These currents were almost completely saturated by sodium concentrations of 20 mM with a Km of about 2.6 mM sodium. Amiloride (10 microM) inhibits the expressed sodium channels entirely and examination of dose response relationships yielded a half-maximal inhibition concentration (Ki) of 120 nM amiloride. I-V difference curves in the presence or absence of sodium or amiloride (10 microM) indicate a potential dependence of the sodium transport which can be described by the Goldman equation. When Na+ is replaced by K+, no amiloride response was detected indicating a high selectivity for Na+ over K+. These results provide strong evidence that intestinal Na+ channels are regulated by dietary salt intake on the RNA level.

Amiloride↗
PubMed1992

Expression of the amiloride-blockable Na+ channel by RNA from control versus aldosterone-stimulated tissue.

The amiloride-blockable Na+ channel was expressed in Xenopus oocytes injected with total RNA isolated from the toad urinary bladder. This system was used to investigate mechanisms that mediate the natriferic action of aldosterone. Incubation of the epithelium with aldosterone for 3 h doubled its channel activity but did not increase the ability of isolated RNA to express functional channels in oocytes. A 20-h incubation with the hormone produced an additional increase of Na+ transport across the intact epithelium and also augmented the channel activity expressed in oocytes by nearly 10-fold. The data are in agreement with our model that aldosterone enhances the apical Na+ permeability of tight epithelia by a short term activation of pre-existing channels, followed by chronic induction of new channel protein. Blocking methyl transfer reactions, previously shown to inhibit the natriferic action of aldosterone in tight epithelia, did not alter the basal or aldosterone-induced response in oocytes.

Aldosterone↗
PubMed1992

NaCl-dependent expression of amiloride-blockable Na+ channel in Xenopus oocytes.

RNA was isolated from chicken lower intestine (both colon and coprodeum) and injected into Xenopus oocytes. 22Na+ fluxes measured after 1-4 days demonstrated the induction of an amiloride-blockable pathway. The Na+ transporter expressed by the exogenous RNA had a high affinity to amiloride (inhibitory constant less than 0.1 microM), but was insensitive to ethylisopropyl amiloride, i.e., it is likely to be the apical Na+ channel. Functional channels were readily expressed in oocytes injected with RNA derived from chickens fed a low-NaCl diet. On the other hand, no channel activity was detected in oocytes injected with RNA isolated from chickens fed a high-NaCl diet. Thus the previously reported regulation of transport by the dietary NaCl intake involves modulations in the level of mRNA that codes either for the Na+ channel or a posttranscriptional regulator of the channel.

Amiloride↗
PubMed1979

Light-induced pH changes in sub-bacterial particles of Halobacterium halobium. Effects of ionophores.

The kinetics of light-induced acidification and of the subsequent dark-induced alkalization in suspensions of sub-bacterial particles of Halobacterium halobium may be expressed as the sum of two exponentials, indicating two processes (Eisenbach, M., Bakker, E.P., Korenstein, R. and Caplan, S.R. (1976) FEBS Lett. 71, 228--232). We studied the effects of carbonyl cyanide p-trifluoromethyoxy phenyl-hydrazone, nigericin, gramicidin D, valinomycin, and monactin on the extents and the rate constants of the two processes. The various ionophores affected the two processes differently and in general the slower process was more sensitive to their presence. Valinomycin and monactin had relatively minor effects, apparently due to the high ionic strength of the suspension. When an artificial membrane potential was created in the dark, the light-induced acidification was preceded by a transient alkalization as is usually observed in intact cells. These results are discussed in the light of a suggested model accounting for the two processes (Caplan, S.R., Eisenbach, M., Cooper, S., Garty, H., Klemperer, G. and Bakker, E.P. (1977) in Bioenergetics of Membranes (Packer, L., Papageorgiou, G.C. and Trebst, A., eds.), pp. 101--114, Elsevier/North-Holland Biomedical Press, Amsterdam), taking into account the different selectivities of the ionophores applied.

Anti-Bacterial Agents↗
PubMed1979

Light-induced conductivity changes in purple membrane suspensions.

Small light-induced changes in the conductivity of light-adapted purple membrane suspended in strong electrolyte solutions were detected. The method used involved modulated light and a phase sensitive detector and it allowed us to detect accurately changes as small as 0.0001% in the conductivity of the suspension. The light-induced conductivity changes turned out to be composed of at least two different event: a small fast increase in conductivity (tau approximately 2 ms) followed by a slower and larger decrease in this parameter (tau = 70 ms-80 ms). The effects of pH and temperature on these changes were studied. Both events reached maximal values around neutral pH and approached zero at both high and low pH's. Heating the suspension decreased the photoconductivity change and Arrhenius plots of the data showed breaks around 31 degrees C. It is suggested that the conductivity changes reflect changes in the surface charge of the membrane and can be used to follow the kinetics of the conformational changes occurring in the system.

Bacteriorhodopsins↗
PubMed1978

Bacteriorhodopsin: lipid environment and conformational changes.

The polar lipids of the purple membrane were exchanged for different phosphatidylcholine species. The resulting complexes had the same protein to lipid-phosphorus ratio as the natural membrane, but only about 0.5-1.0 mole of original lipid was still present per mole of bacteriorhodopsin. In such complexes the bacteriorhodopsin photocycle is slowed down 10-20 times, but the strong protein-protein interaction is not abolished. Due to the slow rate of the photocycle we were able to measure in the light the ratio between net proton release and net accumulation of the last intermediate of the photocycle, the unprotonated M412. This ratio was not constant and equal to 1.0, as expected for a single deprotonation reaction, but varied with pH from 1.5 to 0.4. The variable ratio suggests that light-induced conformational changes occur in the nonchromophore part of the protein, which shift the pKa values of unidentified groups so as to cause binding or release of additional protons. A similar conclusion was drawn from experiments on the kinetics of proton transfer by bacteriorhodopsin in subbacterial particles of Halobacterium halobium and in reconstituted bacteriorhodopsin proteoliposomes. However, in this case light-induced association and dissociation of additional protons occurs simultaneously on different sides of the membrane.

Bacteriorhodopsins↗
PubMed1977

Light-driven sodium transport in sub-bacterial particles of Halobacterium halobium.

Light-induced Na+ efflux was observed in sub-bacterial particles of Halobacterium halobium loaded and suspended in 4 M NaCl solution. The Na+ efflux was not ATP driven, since ATPase inhibitors were without effect or even enhanced efflux at low light intensity. Uncouplers, on the other hand, inhibited Na+ efflux, the inhibition being complete at low light intensity. The Na+ efflux was accompanied by proton influx. Both processes were dependent on light intensity, unaffected or enhanced by ATPase inhibitors and similarly affected by uncouplers. Proton influx was not observed in particles loaded with 4 M KCl instead of 4 M NaCl. Na+ transport in the dark could be induced by artificial formation of a pH difference across the membrane; changing the sign of the pH difference reversed the direction of the Na+ transport. Proton influx in the dark followed the artificial formation of a sodium gradient [Na+]in less than [Na+]out). These results may be explained by a Na+/H+ antiport mechanism. The fluxes of Na+ and H+ were of comparable magnitude, but the initial rate of Cl- efflux in the same experiment was one-third of the initial rate of Na+ efflux. Consequently Cl- is not regarded as a participant in the Na+ efflux mechanism.

Arsenates↗
PubMed1977

Light-depending rubidium transport in intact Halobacterium halobium cells.

The uptake of rubidium in intact Halobacterium halobium cells was followed, and found to be light-dependent. The exchange process is slow, the steady-state rate of 86Rb+/Rb+ exchange being given by k. = 6.3 - 10(-4) min-1. Starved cells exhibited a faster rate than unstarved cells. The influx of 86Rb+ was almost completely blocked in the presence of proton conductors (CCCP, FCCP, and SF 6847), and was sensitive to the presence of the permeant cation TPMP+. Valinomycin very slightly increased the rate of uptake, while 1 - 10(-6) M nigericin showed significant inhibition. On the other hand, release of 86Rb+ was not light-dependent, although still affected by uncouplers, TPMP+, and nigericin. These experimental observations may be explained in terms of a passive flux driven by an electrical potential difference, and influenced by positive isotope interaction within the membrane. In carefully matched influx-efflux studies, the extent of the positive isotope interaction was measured. Using the formal treatment of Kedem and Essig, the ratio (exchange resistance)/(resistance to net flow) for 86Rb+ was found to be 1.7.

Biological Transport, Active↗