Na+/K+-ATPase Inhibition Partially Mimics the Ethanol-Induced Increase of the Golgi Cell-Dependent Component of the Tonic GABAergic Current in Rat Cerebellar Granule Cells

Cerebellar granule cells (CGNs) are one of many neurons that express phasic and tonic GABAergic conductances. Although it is well established that Golgi cells (GoCs) mediate phasic GABAergic currents in CGNs, their role in mediating tonic currents in CGNs (CGN-I_tonic) is controversial. Earlier studies suggested that GoCs mediate a component of CGN-I_tonic that is present only in preparations from immature rodents. However, more recent studies have detected a GoC-dependent component of CGN-I_tonic in preparations of mature rodents. In addition, acute exposure to ethanol was shown to potentiate the GoC component of CGN-I_tonic and to induce a parallel increase in spontaneous inhibitory postsynaptic current frequency at CGNs. Here, we tested the hypothesis that these effects of ethanol on GABAergic transmission in CGNs are mediated by inhibition of the Na⁺/K⁺-ATPase. We used whole-cell patch-clamp electrophysiology techniques in cerebellar slices of male rats (postnatal day 23–30). Under these conditions, we reliably detected a GoC-dependent component of CGN-I_tonic that could be blocked with tetrodotoxin. Further analysis revealed a positive correlation between basal sIPSC frequency and the magnitude of the GoC-dependent component of CGN-I_tonic. Inhibition of the Na⁺/K⁺-ATPase with a submaximal concentration of ouabain partially mimicked the ethanol-induced potentiation of both phasic and tonic GABAergic currents in CGNs. Modeling studies suggest that selective inhibition of the Na⁺/K⁺-ATPase in GoCs can, in part, explain these effects of ethanol. These findings establish a novel mechanism of action of ethanol on GABAergic transmission in the central nervous system.     

Characterization of β-amylase and its deficiency in various rice cultivars

 β-Amylase deficiency in various cultivars of rice was examined at the molecular level. Using an antibody against β-amylase purified from germinating seeds of rice, we were able to demonstrate the expression and organization of the β-amylase gene in normal and deficient cultivars. Although β-amylase is a starch-hydrolyzing enzyme, as is α-amylase, the β-amylase protein/gene is expressed differently from the α-amylase protein/gene; i.e. (1) β-amylase is synthesized only in aleurone cells, (2) the enzyme production in the embryo-less half-seeds is not under hormonal control. We identified some cultivars of rice that are deficient for β-amylase activity. We present new evidence that synthesis is blocked at the level of mRNA synthesis in the deficient cultivars. The usefulness of β-amylase as a crop trait is also discussed. Received: 8 May 1998 / Accepted: 5 June 1998     

The use of volatile cues in recognition of kin eggs by predatory mites

1. Several animal species are known to distinguish between their own eggs and eggs of unrelated conspecifics. However, the cues involved in this discrimination are often unknown. These cues were studied using the predatory mite Gynaeseius liturivorus Ehara.
2. Adult females of these predatory mites oviposit in clusters and avoid oviposition close to eggs laid by other females, resulting in reduced cannibalism between offspring. Because predatory mites are blind, it was tested whether volatiles of eggs were used as a cue for egg recognition.
3. Adult female predatory mites were offered volatile cues of their own eggs and of unrelated conspecific eggs, and females were prevented from contacting the eggs. Predatory mites oviposited closer to their own eggs than to unrelated eggs. This preference was observed even when one own and one unrelated egg were offered as a volatile source.
4. These results suggest that adult female predatory mites can determine kinship using volatiles released from the eggs.

     

Effect of oleic acid on mitochondrial cytochrome c oxidase activity

Both Km and Vmax values of cytochrome c oxidase for cytochrome c were elevated in oleic acid-incorporated mitochondria, whereas the amount of oleic acid incorporated into submitochondrial particles was smaller than that into mitochondria and the fatty acid had little effect on the enzyme activity. The degree of change in the bulk membrane fluidity was, however, almost the same in mitochondria and submitochondrial particles. Solubilized cytochrome c oxidase was insensitive to the effect of oleic acid. Oleic acid may act as a modifier of the interaction between cytochrome c oxidase and membrane lipids.     

Mode of inhibitory action of cholecystokinin in amylase release from isolated rat pancreatic acini--inhibition of secretory process post to protein kinase C-calcium ion systems

The incubation of isolated rat pancreatic acini with low doses (1 x 10(-11)-1 x 10(-10) M) of cholecystokinin-octapeptide (CCK8) induced amylase release. This CCK8-induced amylase release has been shown to be mediated through the protein kinase C activation and the Ca2+ mobilization which are linked to the phospholipase C-mediated hydrolysis of phosphoinositides. However, the incubation of the acini with high doses (1 x 10(-9)-1 x 10(-7) M) of CCK8 reduced amylase release to the level less than that induced by the maximally effective dose (1 x 10(-10) M) of this secretagogue. Under the same conditions, the high doses of this secretagogue did not inhibit the phospholipase C-mediated hydrolysis of phosphoinositides. The stimulatory action of the maximally effective dose of CCK8 in amylase release was mimicked by the simultaneous addition of protein kinase C-activating 12-O-tetradecanoylphorbol-13-acetate (TPA) and Ca2+ ionophore A23187. A high dose (1 x 10(-7) M) of CCK8 reduced the amylase release induced by the combination of TPA and A23187. These results suggest that the high doses of CCK8 inhibit the secretory process post to the protein kinase C-Ca2+ systems and thereby reduce the amylase release induced by the maximally effective dose of CCK8 in rat pancreatic acini.     

Inhibitory effect of very-long-chain monounsaturated fatty-acyl-CoAs on the elongation of long-chain fatty acid in swine cerebral microsomes

Characteristics of condensation and overall elongation of very-long-chain fatty-acyl-CoAs in swine cerebral microsomes were studied using radio high-performance liquid chromatography (RHPLC) and gas chromatography-mass spectrometry (GC-MS). The monounsaturated fatty-acyl-CoA depressed both the condensation and overall elongation activities of endogenous substrates and also of exogenous saturated fatty-acyl-CoA. The extent of the decrease of the elongation activity was dependent on the concentration and the chain length of the exogenous fatty-acyl-CoAs. The dependence of the condensation activity of monounsaturated fatty-acyl-CoA on the concentration of malonyl-CoA suggested that the non-Michaelis-Menten type kinetics was dominant for oleoyl-CoA, however, a normal kinetic pattern was obtained for endogenous palmitoyl-CoA and arachidonoyl-CoA with Km = 37 microM to malonyl-CoA. The condensation activity for icosanoyl-CoA (20:0-CoA) was inhibited by icosenoyl-CoA (20:1-CoA) in a non-competitive manner, which suggested that the condensation enzyme, or at least the active center of the enzyme for icosenoyl-CoA, was different from that for icosanoyl-CoA.     

Enhancement of growth factor-induced DNA synthesis by colon tumor-promoting bile acids in Swiss 3T3 cells. Their different mode of action from that of phorbol esters

In Swiss 3T3 cells, colon tumor-promoting deoxycholate (DOC) enhanced DNA synthesis which was induced by fibroblast growth factor (FGF) in the presence of insulin. This effect was observed only when DOC was added within 10 h after the addition of FGF. DOC by itself did not induce DNA synthesis irrespective of the presence or absence of insulin. Similar results were obtained with other colon tumor-promoting bile acids such as cholate, chenodeoxycholate and taurocholate. In contrast to these bile acids, 12-O-tetradecanoylphorbol-13-acetate (TPA) induced DNA synthesis fully without FGF in the presence of insulin. DOC did not affect TPA-induced DNA synthesis. Prolonged treatment of the cells with phorbol-12,13-dibutyrate caused the down-regulation of the phorbol ester receptor and rendered the cells unresponsive to TPA. In these cells, FGF still induced DNA synthesis in the presence of insulin, but the maximal level was reduced to about one third of that in the control cells. DOC did not enhance this DNA synthesis any more. DOC did not alter the binding of FGF to the cells. These results indicate that colon tumor-promoting bile acids enhance the mitogenic action of FGF and thereby stimulate DNA synthesis, although the phorbol ester substitutes for the mitogenic action of FGF.     

Bile acid metabolism in partially hepatectomized rats

The bile flow and the bile acid secretion, calculated on liver weight basis, increased 12 H and 24 H after 60-70% hepatectomy and returned to the initial levels thereafter. The biliary phospholipid secretion much more increased than bile acids, but the cholesterol secretion decreased. Bile acid composition changed with an increase of the cholic acid group and a decrease of the chenodeoxycholic acid group in both bile and feces. These changes almost disappeared on Day 14. The pool size of bile acid decreased maximally on Day 4 to about 40% of the initial, but the distribution of bile acids in the enterohepatic circulation was not changed. The fecal cholesterol and coprostanol markedly decreased on Day 2 but gradually returned to the initial levels according to the recovery of diet intake. The fecal bile acids decreased on Day 2, increased on Day 4, and returned to the normal range after Day 7. In conclusion, the regenerating liver secretes more bile, bile acids and phospholipids, and less cholesterol than the normal liver. Cholic acid predominates in the bile acids. These changes restored to the initial levels by about one week after the operation.