Relation between microvilli membrane potential and glucose transport capacity of rat small intestine.

Transepithelial electrical potential differences induced by glucose were measured in rat small intestine under conditions of experimental diabetes, application of corticosteroids, adrenalectomy, and inhibition of adrenocortical functions. A close linear correlation between the capacity of monosaccharide absorption and the transepithelial potential difference was found. Microelectrode studies indicated that glucose-induced alterations of the transepithelial potential difference are due to depolarization of the potential difference across the microvilli membrane. Changes in the potential difference across the basolateral plasma membrane were not detectable after addition of glucose.

Effect of diabetes and adrenocortical state on intestinal transport capacity and (Na+ + K+)-activated adenosine triphosphatase activity.

(Na+ + K+)-activated adenosine triphosphatase activity in the mucosal homogenate of rat small intestine estimated under conditions of experimental diabetes, application of corticosteroids, adrenalectomy or inhibition of adrenocortical function suggests a general parallelism between the capacity for monosaccharide absorption and enzyme activity. Studying the kinetic parameters it has been found that the maximal velocities of monosaccharide uptake as well as of (Na+ + K+)-activated adenosine triphosphatase reaction are significantly different, whereas sugar concentrations for halfmaximal transport velocities and enzyme-substrate affinity constants remain unaltered. From studies with purified brush borders and basolateral plasma membranes it has been shown that the activity changes were caused exclusively by that part of (Na+ + K+)-activated adenosine triphosphatase which is localized in the basolateral plasma membranes. The enzyme activity in the brush border region remains unchanged. These findings support a concept of intestinal transport mechanism which suggests that the basolateral part of (Na+ + K+)-activated adenosine triphosphatase is responsible for metabolic energy supply.

[Detection of a Na+-activated, furosemide-inhibited ATPase activity in rat intestinal mucosa]. / Nachweis einer Na+-aktivierbaren, durch Furosemid hemmbaren ATPase-Aktivität in der Dünndarmmukosa der Ratte.

An ouabain-insensitive, Mg++-dependent, Na+-stimulated ATPase activity which is inhibited by furosemide was found in mucosal homogenate of rat small intestine. The subcellular localization of this ATPase activity was studied by means of isolated purified brush borders and basolateral plasma membranes. The results suggest a nearly identical distribution of Na+-activated and (Na+K+)-activated ATPase within the epithelial cells. Under conditions of alloxan and streptozotocin diabetes an increase of both ATPase activities can be found only in the basolateral plasma membranes. These observations agree well with the convective model of intestinal absorption.

[Increase of (Na+ + K+)-activated ATPase activity of basolateral plasma membranes from intestinal mucosa of diabetic rats]. / Anstieg der (Na+ + K+)-aktivierbaren ATPase-Aktivität in den basolateralen Plasmamembranen der Dünndarmmukosa diabetischer Ratten.

A significant increase of the (Na+ + K+)-activated ATPase was found in mucosal homogenates of rat small intestine under conditions of alloxan and streptozotocin diabetes. From studies with isolated plasma membranes it has been shown that the activity changes were caused by that part of the (Na+ + K+)-activated ATPase only which is localized in the basolateral plasma membranes, whereas the enzyme activity in the brush border region remains unchanged. In connection with the enhanced capacity of ion, nonelectrolyte and water absorption in experimental diabetes, our findings support a concept of intestinal transport mechanism which suggest that the basolateral part of the (Na+ + K+)-activated ATPase is responsible for metabolic energy supply. The luminal part of the enzyme may be involved in regulation of passive Na+ influx.

[Effect of pellet size on respiratory activity and motility of cryopreserved spermatocytes]. / Einfluss der Pelletgrösse auf die Atmungsaktivität sowie Motilität kryokonservierter humaner Spermienzellen.

The effect of different pellet volumes at freeze preservation in human semen was studied. It was measured the motility of spermatozoa during an incubation time of several hours at 37 degrees C and the alteration of oxygen consumption after adding rotenone, succinate, digitonine or 2,4-dinitrophenol. - The motility of cryopreserved spermatozoa does not show significant differences after preservation procedure. In respect of oxygen consumption the smallest differences from native material were obtained at a pellet volume of 0,2 to 0,3 cm3. Explanations for this behaviour are discussed.

[Effect of alloxan diabetes on (Na+ + K+)-activated ATPase in brush border membrane of the mucosal cell of rat small intestine]. / Der Einfluss des Alloxandiabetes auf die (Na+ + K+)-aktivierbare ATPase in der Bürstensaummembran der Rattendünndarmmukosa.

In order to elucidate a possible relationship between (Na+ + K+)-activated ATPase and intestinal absorption of actively transported monosaccharides enzyme activity was measured in mucosal cells from alloxan diabetic rats. The general effect of increasing capacity of active, Na+-dependent transport processes in diabetes mellitus is associated with a significantly enhanced (Na+ +K+)-activated ATPase activity in mucosal homogenate from diabetic animals. To study the localization of these effects within the cell we isolated purified brush borders and their substructures. To enable a comparison to be made between preparation procedures of diabetic and control animals the fractions were controlled by electronmicroscopy and by measuring the sucrase activity. In the purified brush border fraction of alloxan treated rats there was no significant increase in (Na+ + K+)-activated ATPase activity. Based on these results we conclude that the (Na+ + K+)-activated ATPase in the basolateral membranes was increased in alloxan diabetes, and it seems very likely that this enzyme is involved in the regulation of Na+-dependent transport processes.

[Monosaccharide-dependent potassium ion influx across the microvilli membrane of the rat jejunum]. / Monosaccharidabhängiger K+-Influx über die Mikrovillimembran des Jejunums der Ratte

1. The condidtions were studied under which the Na+-dependently transported monosaccharides influence the K+-influx across the microvilli membrane of rat jejunum. 2. The Na+-dependent, energy requiring transport of monosaccharides causes a decrease of the K+-influx, whereas monosaccharides metabolizable by the intestinal mucosal cells - under suitable conditions - induce an increase in the K+-influx. 3. These results indicate that the K+-influx may be controlled by an energy dependent system in the microvilli membrane, which is influenced by metabolism and monosaccharide transport. It is discussed that this control system may be a (Na+ + K+)-ATPase.

Subcellular localization of (Na+ + K+)-activated ATPase in the brush border membrane of the mucosal cell of the rat small intestine.

The localization of (Na+ + K+)-activated ATPase was investigated in isolated brush borders of rat small intestinal mucosa. The purity of the fractions has been checked by morphological and enzymatic criteria. The brush borders were found to contain a significant quantity of (Na+ + K+)-activated ATPase. Separation of isolated brush borders into their substructures suggests that (Na+ + K+)-activated ATPase is localized deeper within the brush border region than invertase. These findings are discussed in relation to active monosaccharide transport in the intestine.