Ca2+-activated K+ conductance causes membrane hyperpolarizations in a monkey kidney cell line (JTC-12)

Summary We have previously reported hyperpolarizing membrane potential changes in a monkey kidney cell line (JTC-12) which has characteristics resembling proximal tubular cells. These hyperpolarizations could be observed spontaneously or evoked by mechanically touching adjacent cells. In this report, we have shown further evidence that these hyperpolarizations are elicited by an increase in membrane conductance to K⁺ which is caused by an increase in cytosolic Ca²⁺ concentration. In addition, we have found another type of hyperpolarization which is evoked by applying flow of extracellular fluid to the cell. Intracellular injection of Ca²⁺ and Sr²⁺ evoked hyperpolarizations, while intracellular injection of Mn²⁺ and Ba²⁺ did not. Intracellular injection of EGTA suppressed both spontaneous and mechanically evoked hyperpolarizations. In Ca²⁺-free medium, both spontaneous and flow-evoked hyperpolarizations were not observed, while mechanical stimuli consistently evoked hyperpolarization. In Na⁺-free medium, the incidence of cells showing the spontaneous or flow-evoked hyperpolarization increased, and the amplitude and the duration of the mechanically evoked hyperpolarization became greater. Quinidine inhibited all types of hyperpolarization. These data suggest that hyperpolarizations in JTC-12 cells are due to an increase in Ca²⁺-activated K⁺ conductance.     

Inhibition of rat brain adenylate cyclase activity by benzodiazepine through the effects on Gi and catalytic proteins

The effect of benzodiazepines on adenylate cyclase system was examined in rat brain. Micromolar concentrations of diazepam inhibited the enzyme activity in synaptic membranes in dose- and time-dependent manners. The inhibitory effect of diazepam was more evident on the enzyme activity in the presence of guanylyl-5'-imidodiphosphate (GppNHp) or NaF-AlCl3 than on that in the basal state. In the pertussis toxin-treated membranes, the effect of diazepam in the presence of GppNHp or NaF-AlCl3 was markedly suppressed. In addition, other benzodiazepines, such as medazepam, flurazepam, flunitrazepam, and clonazepam, had similar effects to those of diazepam, whereas Ro15-1788, an antagonist of a high affinity receptor in the central nervous system, had no effect on adenylate cyclase activity and did not antagonize the effect of diazepam. These findings indicate that benzodiazepines inhibit rat brain adenylate cyclase activity through the effects on both a low affinity benzodiazepine receptor coupled with the inhibitory GTP-binding regulatory protein (Gi) and catalytic protein.     

Characterization of a glucuronyltransferase: neolactotetraosylceramide glucuronyltransferase from rat brain

The properties of a rat brain glucuronyltransferase, which is presumed to be associated with the biosynthesis of the HNK-1 epitope on sulfoglucuronyl glycolipids, are described. The enzyme required divalent cations for reaction, with maximal activity at 10mm Mn²⁺, and exhibited a dual optimum at pH 4–5 and pH 6 depending upon the buffer used, with the highest activity at pH 4.5 in MES buffer. This enzyme strictly recognized the Gal1-4GlcNAc terminal structure, and was highly specific for neolacto (type 2) glycolipids as acceptor. The enzyme was localized specifically in the brain, and was barely detected in other issues, including the thymus, spleen, liver, kidney, lung, and sciatic nerve fibres. Phosphatidylinositol and phosphatidylserine increased the enzymatic reaction 4.4- and 2.3-fold, respectively, whereas phosphatidylcholine slightly decreased the rate.Abbreviations GlcA glucuronic acid - Lc-PA₁₄ lactotetraose-phenyl-C₁₄H₂₉ - nLc-PA₁₄ neolactotetraose-phenyl-C₁₄H₂₉ - nLcOse₄-Cer neolactotetraosylceramide - NP-40 Nonidet P-40 - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PS phosphatidylserine - SGGL sulfoglucuronyl glycolipid     

Phosphorus-31 magnetic resonance spectroscopy of forearm flexor muscles in student rowers using an exercise protocol adjusted for differences in cross-sectional muscle area

To assess exercise energy metabolism of forearm flexor muscles in rowers, six male student rowers and six control subjects matched for age and sex were studied using phosphorus-31 magnetic resonance spectroscopy (31P-MRS). Firstly, to adjust for the effect of differences in cross-sectional muscle area, the maximal cross-sectional area (CSAmax) of the forearm flexor muscles was estimated in each individual using magnetic resonance imaging. Multistage exercise was then carried out with an initial energy production of 1 J.cm-2 CSAmax for 1 min and an increment of 1 J.cm-2 CSAmax every minute to the point of muscle exhaustion. A series of measurements of 31P-MRS were performed every minute. The CSAmax was significantly greater in the student rowers than in the control subjects [19.8 (SD 2.2) vs 17.1 (SD 1.2) cm2, P less than 0.05]. The absolute maximal exercise intensity (J.min-1) was greater in the rowers than in the control subjects. However, the maximal exercise intensity per unit of muscle cross sectional area (J.min-1.cm-2) was not significantly different between the two groups. During mild to moderate exercise intensities, a decrease in phosphocreatine and an increase in inorganic phosphate before the onset of acidosis were significantly less in the rowers, indicating a requirement of less adenosine 5'-diphosphate to drive adenosine 5'-triphosphate production. The onset of acidosis was also significantly delayed in the rowers. No difference was observed in forearm blood flow between the two groups at the same exercise intensity (J.min-1.cm-2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Enclosure experiment on the control mechanism of planktonic bacterial standing stock

In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the different enclosures ranged from 1.2 to 2.7×10⁷ cells mL⁻¹ throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was 6.3×10⁵ cells mL⁻¹ h⁻¹. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already stocked in the water column, though it is not known whether the dominant bacteria were the same.     

A novel and efficient method for enzymatic synthesis of high purity maltose using moranoline (1-deoxynojirimycin).

A transglycosylation reaction with moranoline (1-deoxynojirimycin) was done with soluble starch as the glucosyl donor and Bacillus macerans amylase as a cyclodextrin glycosyltransferase [EC 2.4.1.19]. The resultant transglycosylation products with moranoline, obtained by treating the reaction mixture with a strong cation exchange resin, were hydrolyzed by beta-amylase [EC 3.2.1.2] from sweet potatoes. The hydrolysate was treated with a strong cation exchange resin, and high purity maltose was obtained.     

Changes in plant growth processes under microgravity conditions simulated by a three-dimensional clinostat

We developed a three-dimensional (3-D) clinostat to simulate a microgravity environment and studied the changes in plant growth processes under this condition. The rate of germination of cress (Lepidium sativum), maize (Zea mays), rice (Oryza sativa), pea (Pisum sativum), or azuki bean (Vigna angularis) was not affected on the clinostat. The clinostat rotation did not influence the growth rate of their roots or shoots, except for a slight promotion of growth in azuki roots and epicotyls. On the contrary, the direction of growth of plant organs clearly changed on the 3-D clinostat. On the surface of the earth, roots grow downward while shoots upward in parallel to the gravity vector. On the 3-D clinostat, roots of cress elongated along the direction of the tip of root primordia after having changed the direction continuously. Rice roots also grew parallel to the direction of the tip of root primordia. On the other hand, roots of maize, pea, and azuki bean grew in a random fashion. The direction of growth of shoots was more controlled even on the 3-D clinostat. In a front view of embryos, shoots grew mostly along the direction of the tip of primordia. In a side view, rice coleoptiles showed an adaxial (toward the caryopsis) while coleoptiles of maize and epicotyls of pea and azuki bean an abaxial curvature. The curvature of shoots became larger with their growth. Such an autotropism may have an important role in regulation of life cycle of higher plants under a microgravity environment.     

Effect of various factors on serotonin-induced Ca2+ response in human platelets

Serotonin (5-HT)-stimulated intracellular Ca2+ concentration change was studied in the platelets of healthy subjects, using fluorescent Ca indicator fura-2. 5-HT increased the Ca2+ response in a concentration-dependent manner. 10 microM of 5-HT induced the maximal response and its EC50 value was 0.4 microM. This response was potently inhibited by selective 5-HT2 antagonists, suggesting that 5-HT-induced Ca2+ mobilization in human platelets is mediated by 5-HT2 receptors. This 5-HT2-mediated Ca2+ response was not significantly affected by the time of blood sampling, gender, meal or exercise. However, this response declined with time after blood drawing, suggesting that it must be measured as soon as possible after sampling. These results indicate that 5-HT-stimulated Ca2+ response in human platelets is a stable parameter and that it will be suitable for assessing 5-HT2 receptor function in depressed patients.