scholarly journals Lactic acid secretion by human neutrophils. Evidence for an H+ + lactate- cotransport system.

1992 ◽  
Vol 100 (2) ◽  
pp. 341-367 ◽  
Author(s):  
L Simchowitz ◽  
J A Textor
Keyword(s):  
Lactic Acid ◽  
Steady State ◽  
Ph Dependence ◽  
Transport Systems ◽  
Human Neutrophils ◽  
Bathing Medium ◽  
Monocarboxylate Transport ◽  
Cotransport System ◽  
Ph Stat ◽  
Transport In Mitochondria

The pathway by which L-lactate (Lac) crosses the plasma membrane of isolated human neutrophils was investigated. The influx of [14C]Lac from a 2 mM Lac, 145 mM Cl-, 5.6 mM glucose medium was approximately 1.5 meq/liter of cell water.min and was sensitive to the organomercurial agent mersalyl (apparent Ki approximately 20 microM), to alpha-cyano-4-hydroxycinnamate (CHC), the classical inhibitor of monocarboxylate transport in mitochondria, and to UK-5099 (apparent Ki approximately 40 microM), a more potent analogue of CHC. Transport was also strongly blocked (greater than 80%) by 1 mM of either 3,5-diiodosalicylic acid, MK-473 (an indanyloxyacetate derivative), or diphenyl-amine-2-carboxylate, and by 0.4 mM pentachlorophenol, but not by 1 mM ethacrynic acid, furosemide, or the disulfonic stilbenes SITS or H2DIDS. One-way [14C]Lac efflux from steady-state cells amounted to approximately 6 meq/liter.min and was likewise affected by the agents listed above. Influx, which was membrane potential insensitive and Na+ independent, displayed a strong pH dependence: extracellular acidification enhanced uptake while alkalinization inhibited the process (pK' approximately 5.7 at 2 mM external Lac). The rate of [14C]Lac influx was a saturable function of external Lac, the Km being approximately 7 mM. Steady-state cells exhibited an intracellular Lac content of approximately 5 mM and secreted lactic acid into the bathing medium a a rate of approximately 4 meq/liter.min. Secretion was completely suppressed by 1 mM mersalyl which inactivates the carrier, leading to an internal accumulation of Lac. That the Lac carrier truly mediates an H+ + Lac- cotransport (or formally equivalent Lac-/OH- exchange) was documented by pH-stat techniques wherein an alkalinization of poorly buffered medium could be detected upon the addition of Lac; these pH changes were sensitive to mersalyl. Thus, the Lac carrier of neutrophils possesses several features in common with other monocarboxylate transport systems in erythrocytes and epithelia.

Conservative and nonconservative inhibitors of gastric acid secretion

1987 ◽  
Vol 253 (3) ◽  
pp. G359-G368 ◽  
Author(s):  
E. B. Ekblad ◽  
V. Licko
Keyword(s):  
Steady State ◽  
Acid Secretion ◽  
Initial Step ◽  
No Net Loss ◽  
Apparent Loss ◽  
H2 Antagonist ◽  
Flow Through ◽  
Ph Stat ◽  
High Concentrations ◽  
Continuous Presence

Inhibitors of the initial step (H2-antagonist) and of the final step (thiocyanate, SCN-; and nitrite, NO2-) were used to study the dynamics of acid secretion in isolated frog gastric mucosa. Tissues were mounted in flow-through chambers, and the acid secretion rate (SR) was recorded on a pH-stat microprocessor. Continuous presence of H2-antagonist decreases the SR to a lower steady state, and on removal the SR returns to basal SR, causing a net loss of acid, the nonconservative effect. The amount of lost acid is a unique function of exposure, thus, independent of the patterns (pulses or steps) of inhibition. In contrast, continuous presence of SCN- or NO2- (below 3 mM) results in an undershoot in SR with a return to basal SR, whereas at higher concentrations there is no return. Removal of these inhibitors causes an overshoot in SR with return to basal SR. The rebound acid is equal to acid suppressed by NO2- and low concentration of SCN-, resulting in no net loss of acid, the conservative effect, whereas at high concentrations of SCN- there is an apparent loss of acid. In maximally secreting tissue the overshoot of SR is not observed. However, the acid is not lost, merely delayed. In resting tissue NO2- also merely delays the exit of the acid produced in response to forskolin. The rebound acid is proposed to reside in a sequestered "acid" pool that is stable for at least 120 min. Results with NO2- and SCN- suggest an effect on a saturable exit enzyme, possibly the K+-H+-ATPase.

pH dependence of kinetics and steady-state block of cardiac sodium channels by lidocaine

1993 ◽  
Vol 264 (5) ◽  
pp. H1588-H1598 ◽  
Author(s):  
D. J. Wendt ◽  
C. F. Starmer ◽  
A. O. Grant
Keyword(s):  
Steady State ◽  
Sodium Channel ◽  
Local Anesthetic ◽  
Ph Dependence ◽  
Membrane Depolarization ◽  
Low Ph ◽  
Proton Exchange ◽  
Phasic Block ◽  
Cardiac Sodium Channels ◽  
External Ph

The local anesthetic-class antiarrhythmic drugs produce greater depression of conduction in ischemic compared with normal myocardium. The basis for this relatively selective action is uncertain. A model of the pH-dependent interaction of tertiary amine drugs with the sodium channel suggests that the low pH occurring during ischemia slows drug dissociation from the channel by changing the drug's protonation. The importance of the proton exchange reaction and the effect of overall slowing of drug dissociation on steady-state sodium channel blockade is uncertain. We have measured whole cell sodium channel current in rabbit atrial myocytes during control and exposure to lidocaine while external pH was varied between 6.8 and 7.8 at membrane potentials of -140, -120, and -100 mV. Tonic blockade was little influenced by external pH. Decreasing the external pH from 7.8 to 6.8 slowed both the rate of development of phasic block and recovery from the block. Decreasing the membrane potential from -140 to -100 mV increased the degree of phasic block attained in the steady state. Block was further enhanced when low pH was combined with membrane depolarization. Experiments in which deuterium ions were substituted for protons suggest that the kinetics of proton exchange is not rate limiting in the dissociation of drugs from the sodium channel. We conclude that it is the combined effect of low pH and membrane depolarization that may be critical in the enhanced blocking action of local anesthetic-class drugs during ischemia.

scholarly journals Studies on the electron-transfer mechanism of the human neutrophil NADPH oxidase

1989 ◽  
Vol 262 (2) ◽  
pp. 575-579 ◽  
Author(s):  
J A Ellis ◽  
A R Cross ◽  
O T G Jones
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Nadph Oxidase ◽  
Cytochrome B ◽  
Human Neutrophil ◽  
Sodium Deoxycholate ◽  
Human Neutrophils ◽  
Electron Transfer Mechanism ◽  
State Reduction ◽  
O2 Production

A superoxide-generating NADPH oxidase was solubilized from phorbol 12-myristate 13-acetate-activated human neutrophils with a mixture of sodium deoxycholate (0.125%, w/v) and Lubrol-PX (0.125%, v/v). The solubilized preparation contained FAD (577 pmol/mg of protein) and cytochrome b-245 (479 pmol/mg of protein) and produced 11.61 mol of O2-./s per mol of cytochrome b (340 nmol of O2-./min per mg of protein). On addition of NADPH, the cytochrome b-245 was reduced by 7.9% and the FAD by 38% in the aerobic steady state; NADH addition caused little steady-state reduction of cytochrome b and FAD. In this preparation, and several others, the measured rate of O2-. production correlated with the turnover of cytochrome b calculated from the extent of cytochrome b-245 reduction under aerobic conditions. Addition of diphenyleneiodonium abolished the reduction of both the FAD and cytochrome b-245 components and inhibited O2-. production. The haem ligand imidazole inhibited O2-. generation and cytochrome b reduction while permitting FAD reduction. These results support the suggestion that the human neutrophil NADPH oxidase has the electron-transport sequence: NADPH-FAD-cytochrome b-245-O2.

Responses of trout gill ion transport systems to acute acidosis

1976 ◽  
Vol 64 (2) ◽  
pp. 511-515
Author(s):  
T. H. Kerstetter ◽  
R. Mize
Keyword(s):  
Lactic Acid ◽  
Rainbow Trout ◽  
Ion Transport ◽  
Ion Uptake ◽  
Transport Systems ◽  
Ph Changes ◽  
Blood Ph ◽  
Slow Infusion ◽  
Trout Gill

The response of rainbow trout Na+ and Cl- uptake systems to acute acidosis was tested by slow infusion of lactic acid into anaesthetized animals. Depression of blood pH by 0–4 pH unit had no effect on influx rates for either ion, and we conclude that gill ion uptake systems do not respond rapidly to blood pH changes.

Bicarbonate Transport Systems in the Intestine of the Seawater EEL

1990 ◽  
Vol 150 (1) ◽  
pp. 381-394 ◽  
Author(s):  
MASAAKI ANDO ◽  
M. V. SUBRAMANYAM
Keyword(s):  
Latent Period ◽  
Water Transport ◽  
Basolateral Membrane ◽  
Transport Systems ◽  
Bicarbonate Transport ◽  
Ph Stat ◽  
Stat Method

Utilizing a pH-stat method, the rates of mucosal and serosal alkalinization were measured separately in the seawater eel intestine. These two rates were dependent on contralateral HCO3− concentration and were inhibited by contralateral application of DIDS, an inhibitor of HCO3− transport, indicating that the mucosal and serosal alkalinization are due to HCO3− secretion and absorption, respectively. The mucosal alkalinization was enhanced after inhibiting Na+/K+/Cl− cotransport by treatment with bumetanide, furosemide or Ba2+, with a latent period of more than lOmin, suggesting that HCO3− absorption from mucosa to serosa depends on Na+/K+/Cl− cotransport. The serosal alkalinization caused by HCO3− absorption was completely abolished after mucosal application of bumetanide. After pretreatment with bumetanide, mucosal omission of Cl− halved the enhanced rate of mucosal alkalinization, and Na+ omission had no effect on it; this indicates that the exit of HCO3− into the lumen depends on luminal Cl−, i.e. on the existence of the usual C1−/HCO3− exchange on the brushborder membrane. When serosal Na+ was removed under the same conditions, mucosal alkalinization was reduced, indicating that HCO3− entry from the serosal fluid depends on Na+. Serosal omission of Cl− did not reduce mucosal alkalinization. In addition, serosal alkalinization was enhanced by serosal removal of Na+ but not of Cl−. These results suggest that there is a Na+/HCO3− cotransport on the basolateral membrane. A possible model for HCO3− transport systems in the seawater eel intestine is proposed, and a possible role for these transport systems is discussed in relation to Na+, Cl− and water transport.

P-glycoprotein-mediated secretion of a fluorescent cyclosporin analogue by teleost renal proximal tubules

1995 ◽  
Vol 268 (1) ◽  
pp. F46-F52 ◽  
Author(s):  
U. Schramm ◽  
G. Fricker ◽  
R. Wenger ◽  
D. S. Miller
Keyword(s):  
Steady State ◽  
Fluorescence Intensity ◽  
Fundulus Heteroclitus ◽  
Organic Anion ◽  
Proximal Tubules ◽  
Metabolic Inhibitors ◽  
Epifluorescence Microscopy ◽  
Transport Systems ◽  
Simple Diffusion ◽  
P Glycoprotein

The transport of a fluorescent cyclosporin analogue was measured in killifish (Fundulus heteroclitus) proximal tubules by means of epifluorescence microscopy and digital image analysis. Renal cells rapidly accumulated the cyclosporin analogue from the medium and attained steady state within 60 min; luminal fluorescence increased over the first 60-90 min. At steady state, luminal fluorescence intensity was two to three times higher than cellular. Cellular fluorescence intensity was a linear function of medium substrate concentration and was not affected by any treatment used. In contrast, luminal fluorescence exhibited a saturable component as the medium concentration of the cyclosporin was increased. Secretion into the lumen was blocked by metabolic inhibitors, vanadate, other cyclosporins, such as cyclosporin A and cyclosporin G, and substrates for P-glycoprotein (verapamil, vinblastine, and quinine) but not by substrates for the renal organic anion or organic cation transport systems, such as p-aminohippurate or tetraethylammonium. The data are consistent with the fluorescent cyclosporin analogue entering proximal tubule cells by simple diffusion and then being pumped into the tubular lumen by P-glycoprotein.

Kinetic analysis of batch and continuous culture of Streptococcus cremoris HP

1978 ◽  
Vol 24 (4) ◽  
pp. 372-380 ◽  
Author(s):  
P. L. Rogers ◽  
L. Bramall ◽  
I. J. McDonald
Keyword(s):  
Lactic Acid ◽  
Steady State ◽  
Kinetic Analysis ◽  
Continuous Culture ◽  
Batch Culture ◽  
Lactic Acid Production ◽  
Streptococcus Cremoris ◽  
Lactose Utilization ◽  
State Growth ◽  
Batch Data

The growth of Streptococcus cremoris on a semidefined medium was studied at initial lactose concentrations of 0.2–5.0% in batch culture, and in lactose-limited chemostat cultures at 0.5% lactose. Kinetic analysis of the batch data, using statistical techniques, indicated the importance of lactose limitation and lactic acid inhibition of the growth of S. cremoris. A model for the biomass production, lactose utilization, and lactic acid production in batch culture was proposed. In continuous culture, it was found that steady state populations were maintained at higher dilution rates (D = 0.6–0.7 h−1) than the maximum predicted by batch culture (0.56 h−1). No evidence for a selection of fast-growing mutants was obtained. Copious growth adhering to the walls of the fermentor (i.e. wall growth) occurred very rapidly at higher dilution rates and this undoubtedly affected steady-state growth and wash-out and, as a consequence, the apparent maximum dilution rate.

Sign in / Sign up

Export Citation Format

Share Document