Ureagenesis in the liver consumes up to 1,000 mmol of HCO3-/day in humans as a result of 2NH4+ + 2HCO3- --> urea + CO2 + 3H2O. Whether the liver contributes to the regulation of acid-base equilibrium by controlling the rate of ureagenesis and, therefore, HCO3- consumption in response to changes in plasma acidity has not been adequately evaluated in humans. Rates of ureagenesis were measured in ...

Bicarbonate provides the dominant pH buffer of the cochlear fluids. In the present study, perilymph bicarbonate concentration was manipulated during which endocochlear potential, cochlear fluids pH and cochlear sensitivity to sounds were monitored. Perilymphatic perfusion of medium containing elevated HCO3, at higher pH than normal, produced a decrease in endolymph pH. Similarly, perfusion of n...

Membrane-bound luminal carbonic anhydrase (CA) IV, by catalyzing the dehydration of carbonic acid into CO2 plus water, facilitates H+ secretion in the renal outer medullary collecting duct from the inner stripe (OMCDi). To examine the role of CA IV on H+ secretion, we measured net HCO3- transport in perfused OMCDi segments and examined the effect on transport of two extracellular CA inhibitors,...

Intestinal endocrine cells release gut hormones, including glucagon-like peptides (GLPs), in response to luminal nutrients. Luminal L-glutamate (L-Glu) and 5'-inosine monophosphate (IMP) synergistically increases duodenal HCO3- secretion via GLP-2 release. Since L cells express the bile acid receptor TGR5 and dipeptidyl peptidase (DPP) IV rapidly degrades GLPs, we hypothesized that luminal amin...

A large alkaline tide (up to 20 mmol l(-1) increase in bicarbonate concentration [HCO3-] with an accompanied increase in blood pH) has previously been reported for some carnivorous reptiles within 24 h after ingesting a large meal. This phenomenon has been attributed to the secretion of large amounts of H+ ions into the stomach, which is required for digestion of large prey items. To test the g...

The midpoint potential (Em) of [Formula: see text], the one-electron acceptor quinone of Photosystem II (PSII), provides the thermodynamic reference for calibrating PSII bioenergetics. Uncertainty exists in the literature, with two values differing by ∼80 mV. Here, we have resolved this discrepancy by using spectroelectrochemistry on plant PSII-enriched membranes. Removal of bicarbonate (HCO3-)...

At physiological concentrations of HCO3- and CO2, Mn(II) catalyzes disproportionation of H2O2. This catalase-like activity is directly proportional to the concentrations of Mn(II) and H2O2, and it increases exponentially with increases in pH. The effect of increasing pH is almost completely attributable to the concomitant increase in HCO3- concentration. The rate is proportional to the third po...

We have previously shown that continuous intravenous infusion of NaHCO3 for 24 h ( approximately 1000 micromol kg(-1) h(-1)) results in the relocation of V-H+-ATPase from the cytoplasm to the basolateral membrane in the gills of the Pacific dogfish. To further investigate this putative base-secretive process we performed similar experiments with the addition of colchicine, an inhibitor of cytos...

In the intact eye, the transition from light to dark alters pH, [Ca2+], and [K] in the subretinal space (SRS) separating the photoreceptor outer segments and the apical membrane of the retinal pigment epithelium (RPE). In addition to these changes, oxygen consumption in the retina increases with a concomitant release of CO2 and H2O into the SRS. The RPE maintains SRS pH and volume homeostasis b...