Protons secretion

P. Imas, B. Bar-Yosef, U. Kakafi, and R. Ganmore-Neumann, Carboxylic anions and proton secretion by tomato roots in response to ammonium/nitrate ratio and pH in nutrient. solution. Plant Soil 191 (1997). 

Precellular solute ionization dictates membrane permeability dependence on mucosal pH. Therefore, lumenal or cellular events that affect mucosal microclimate pH may alter the membrane transport of ionizable solutes. The mucosal microclimate pH is defined by a region in the neighborhood of the mucosal membrane in which pH is lower than in the lumenal fluid. This is the result of proton secretion by the enterocytes, for which outward diffusion is slowed by intestinal mucus. (In fact, mucosal secretion of any ion coupled with mucus-restricted diffusion will provide an ionic microclimate.) Important differences in solute transport between experimental systems may be due to differences in intestinal ions and mucus secretion. It might be anticipated that microclimate pH effects would be less pronounced in epithelial cell culture (devoid of goblet cells) transport studies than in whole intestinal tissue. 

The excretion of water soluble waste via the kidneys requires filtration followed by selective reabsorption from and secretion into the renal tubules. Regulation of normal blood pH within very strict limits due to proton secretion and bicarbonate reabsorption is a major role of the kidney. 

Overall, for each bicarbonate ion filtered, one has been returned to the blood that is sodium bicarbonate has been reabsorbed and the glomerular filtrate leaving the PCT has a greatly reduced bicarbonate concentration. The relatively small amount of proton secreted by the PCT cell and not used to protonate filtered bicarbonate... 

Figure 8.4 Rote of carbonic anhydrase in proton secretion and bicarbonate reabsorption...

Gorodeski GI [2005] Effects of estrogen on proton secretion via the apical membrane in vaginal-ectocervical epithelial cells of postmenopausal women. Menopause 12 679-684... 

The basal rate of proton secretion is around 10% of maximal but the perception of food (smell, taste, sight or even just the thought of it) increases secretion. This is the cephalic effect of food. Nervons signals from the brain canse release of acetylcholine, histamine and gastrin to stimnlate acid secretion from the parietal cells. When food actnally reaches the stomach, distension, proteins, peptides and amino acids farther stimulate the release of gastrin. 

Boron also appears to be involved in redox metabolism in cell membranes. Boron deficiency was shown to inhibit membrane H -ATPase isolated from plant roots, and H -ATPase-associated proton secretion is decreased in boron-deficient cell cultures [71]. Other studies show an effect of boron on membrane electron transport reactions and the stimulation of plasma reduced nicotinamide adenine dinucleotide (NADH) oxidase upon addition of boron to cell cultures [72, 73]. NADH oxidase in plasma membrane is believed to play a role in the reduction of ascorbate free radical to ascorbate [74]. One theory proposes that, by stimulating NADH oxidase to keep ascorbate reduced at the cell wall-membrane interface, the presence of boron is important in... 

A potassium chloride co-transporter must be closely related to the H /K -ATPase during proton secretion. Potassium and chloride ions move across the apical membrane together with secreted protons Figure 4.1) [15-17]. Potassiiun is recycled while hydrochloric acid of the gastric juice is formed by chloride ions together with the secreted protons. Stimulation of gastric acid secretion across the apical membrane may predominantly reflect the activation or insertion of an active potassium chloride co-transporter rather than direct activation of HVK -ATPase [1]. 

Of possible relevance in this respect are the observations that BS and auxin appear to produce opposite effects in root systems whereas they usually act in a similar (but not identical) way on the shoot and commonly show important interactive effects. The most strikingly different effects of these two compounds in roots relate to adventitious root formation in cuttings which is inhibited by BS (24, 30, 31) and promoted by auxin (24), and proton secretion and membrane potential in root segments which are enhanced and hyper-polarized respectively by BS and inhibited and depolarized respectively by auxin (39, 40). These data could suggest either that BS act independently of auxin in roots or that they antagonize... 

Auxin is known to stimulate proton secretion from the cytosol to the cell wall matrix. BR also does the same in cucumber hypocotyl sections as has been reported for other plant materials (16-20). When sections with the epidermis peeled off are incubated in a weakly alkaline buffer, the pH of the buffer drops considerably, indicating that protons are secreted from the tissue to the medium. BR at 10 nM and IAA at 10 iM are almost equally effective (Figure 5). The interaction of BR and IAA is rather inhibitory at the early period of incubation. However, proton secretion continues longer in the presence of both BR and IAA, and finally exceeds those by BR or IAA alone. BR behaves similarly to IAA in this effect. 

Figure 5. Effects of Brassinolide and IAA on proton secretion from peeled hypocotyl sections.

Self-referencing ion-selective electrodes have seen attractive applications in a diversity of medical problems. For example, the vacuolar-type H+-ATPase has been shown to play an important role in the acidification of the lumen of the proximal vas deferens, part of the male reproductive system. An acidic luminal fluid is required for the maintenance of sperm quiescence and for the prevention of premature activation of acrosomal enzymes during their storage in the epididymis and vas deferens. Proton secretion in the proximal vas deferens has been measured with the self-referencing technique (Fig. 6) [40]. Likewise, altered potassium homeostasis is indicative of dying cells, as the transplasma membrane potential is no longer maintained, as measured in both viable and nonviable embryos [41]. 

Fig. 6 Representative trace showing effects of diphenylamine-2-carboxylate (DPC), 4-acetamido-4 -isothiocyanostilbene-2,2 -disulfonic acid (SITS), and bafilomycin on rate of proton secretion. Addition of 0.5 mM DPC had no effect, and 1 mM SITS strongly inhibited...

On activation of the proton pump, it would be anticipated that the parietal cell becomes more alkaline, because for each proton secreted, an equivalent OH, rapidly converted to HCO3- by carbonic anhydrase, is accumulated within the cell. However, experimental measurements during stimulation of add secretion indicate only a small or no change in pH, compared to the nonstimulated state. 

Wingo CS, Armitage FE (1993) Rubidium absorption and proton secretion by rabbit outer... 

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