Horseradish peroxidase (HRP) was used to investigate whether benfluron (a potential cytostatic drug) can be biotransformed extra-hepatically by systems other than flavin-containing monooxygenase and cytochromes P450. Three types of incubation mixtures differing in buffers (Na-phosphate buffer 50 mmol/l, pH 6.8 and 8.4 and Tris-HCl buffer 25 mmol/l, pH 7.5) were tested. The amount of N-demethyla...

Na(+)/H(+) exchangers are a family of ubiquitous membrane proteins. In higher eukaryotes they regulate cytosolic pH by removing an intracellular H(+) in exchange for an extracellular Na(+). In yeast and Escherichia coli, Na(+)/H(+) exchangers function in the opposite direction to remove intracellular Na(+) in exchange for extracellular H(+). Na(+)/H(+) exchangers display an internal pH-sensitiv...

Fluid secretion and intracellular pH were measured in isolated mosquito Malpighian tubules to determine the presence of Na(+)/H(+) exchange. Rates of fluid secretion by individual Malpighian tubules in vitro were inhibited by 78% of control in the presence of 100 microM 5-(N-ethyl-n-isopropyl)-amiloride (EIPA), a specific inhibitor of Na(+)/H(+) exchange. Steady-state intracellular pH was measu...

The intestinal absorption of many nutrients and drug molecules is mediated by ion-driven transport mechanisms in the intestinal enterocyte plasma membrane. Clearly, the establishment and maintenance of the driving forces - transepithelial ion gradients - are vital for maximum nutrient absorption. The purpose of this study was to determine the nature of intracellular pH (pH(i)) regulation in res...

An electroneutral Na+/H+exchange mechanism (dimethylamiloride inhibitable, Li+ sensitive, and Ca2+ insensitive) was identified in brush-border membrane vesicles (BBMV) from Kuruma prawn hepatopancreas by monitoring Na+-dependent H+ fluxes with the pH-sensitive dye acridine orange and measuring22Na+uptake. Kinetic parameters measured under short-circuited conditions were the Na+ concentration th...

The foregone studies have shown that nicotinic acid cannot produce noticeable reductive signal at carbon-based electrodes without appropriate modification of the electrode. This is an obvious reason that mercury is known as the main electrode material for electro-reduction of nicotinic acid. In this study, it has been shown that it is possible to create a remarkable reduction signal for NA at a...

Chimeras of the catalytic subunits of the gastric H,K-ATPase and Na, K-ATPase were constructed and expressed in LLC-PK1 cells. The chimeras included the following: (i) a control, H85N (the first 85 residues comprising the cytoplasmic N terminus of Na,K-ATPase replaced by the analogous region of H,K-ATPase); (ii) H85N/H356-519N (the N-terminal half of the cytoplasmic M4-M5 loop also replaced); a...

Apical membrane H+ extrusion in the renal outer medullary collecting duct, inner stripe, is mediated by a Na(+)-independent H+ pump. To examine the regulation of this transporter, cell pH and cell Ca2+ were measured microfluorometrically in in vitro perfused tubules using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and fura-2, respectively. Apical membrane H+ pump activity, assayed as cell ...

Extracellular acidification is known to decrease the conductance of many voltage-gated potassium channels. In the present study, we investigated the mechanism of H(+)(o)-induced current inhibition by taking advantage of Na(+) permeation through inactivated channels. In hKv1.5, H(+)(o) inhibited open-state Na(+) current with a similar potency to K(+) current, but had little effect on the amplitu...