ATP-regulated K+ channel and cytosolic Ca2+ mobilization in cultured rat spinal neurons.

ATP activated the K+ channel responsible for outwardly rectifying currents via a P2Y purinoceptor linked to a pertussis toxin-insensitive G-protein in cultured rat spinal neurons. The evoked currents were inhibited by a selective protein kinase C inhibitor, GF109203X, whereas a phospholipase C inhibitor, neomycin had no effect. These indicate that the currents are regulated by phospholipase C-independent protein kinase C activation.

Arachidonic acid potentiates ACh receptor currents by protein kinase C activation but not by receptor phosphorylation.

The effects of arachidonic acid on ACh-gated channel currents were examined using Torpedo nicotinic ACh receptors expressed in Xenopus oocytes. Arachidonic acid decreased ACh-evoked currents during treatment, to a greater extent in Ca(2+)-free extracellular solution. The currents were enhanced for more than 30 min after washing, reaching 150 and 170% in Ca(2+)-containing and -free extracellular solutions, respectively.

Repetitive applications of ATP potentiate potassium current by Ca2+/calmodulin kinase in cultured rat hippocampal neurons.

ATP evoked whole-cell potassium currents in hippocampal neurons. The second application of ATP to the same cell potentiated the current amplitude to around 140% and the current potentiation was maintained by further applications. A calmodulin inhibitor, W-7, or a selective Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibitor, KN-62, inhibited the current potentiation, although a selective protein kinase C inhibitor, GF109203X, or a selective cAMP-dependent protein kinase inhibitor, H-89, had no effect.

Regulation of the serum-activated Ca(2+)-dependent chloride channel in Xenopus oocytes.

Fetal bovine serum evoked Ca(2+)-dependent chloride currents with two components in Xenopus oocytes. The evoked currents were inhibited by GDP beta S, but not by pertussis toxin (PTX). An inositol 1,4,5-triphosphate (IP3) receptor antagonist, heparin completely inhibited the currents, although a phospholipase C inhibitor, neomycin had no effect.

Regulation of the potassium current and cytosolic Ca2+ release induced by 2-methylthio ATP in hippocampal neurons.

A potent P2Y purinoceptor agonist, 2-methylthio ATP (2-MeSATP), produced whole-cell potassium currents through a purinoceptor linked to a pertussis toxin (PTX)-insensitive G-protein in rat hippocampal neurons. The currents were not affected by a selective protein kinase C or A inhibitor. Single channel recordings demonstrated that the potassium channel is activated without latency even in outside-out patches.

P2 purinoceptor-operated potassium channel in rat cerebellar neurons.

P2 purinoceptor agonists produced whole-cell potassium currents in cerebellar neurons with the order of potency 2-methylthio ATP (2-MeSATP) > ADP > ATP > adenosine > alpha,beta- methylene ATP > AMP > UTP. In the outside-out patch clamp configuration, 2-MeSATP evoked single channel currents with two major classes of slope conductances without latency. The currents were blocked by a G-protein inhibitor, GDP beta S, although they were not affected by a phospholipase C inhibitor, a selective protein kinase C or A inhibitor.

Adenosine evokes potassium currents by protein kinase C activated via a novel signaling pathway in superior colliculus neurons.

Adenosine evoked whole-cell potassium currents and enhanced intracellular free Ca2+ concentration ([Ca2+]i) in superior colliculus neurons through a P2Y purinoceptor linked to a pertussis toxin-insensitive G-protein, possibly Gq-protein, which is involved in a protein kinase C (PKC) activation pathway. The [Ca2+]i increase was inhibited by a phospholipase C (PLC) inhibitor, whereas the evoked currents were not affected by a PLC inhibitor or a phospholipase A2 (PLA2) inhibitor. Adenosine elicited single channel currents via PKC activation in cell-attached patches and furthermore, those currents with conductances of the same slope were induced even in excised patches, suggesting that PKC can be activated only by cell membrane factors without intracellular components.

Lysophosphatidylcholine inhibits NMDA-induced currents by a mechanism independent of phospholipase A2-mediated protein kinase C activation in hippocampal glial cells.

Lysophosphatidylcholine (LysoPC), which is formed by phospholipase A2 (PLA2)-mediated phosphatidylcholine hydrolysis, is involved in enhancement of the diacylglycerol- or phorbol ester-dependent protein kinase C (PKC) activation. In the present study, the effect of lysoPC on NMDA-evoked currents was examined by whole-cell patches in cultured rat hippocampal glial cells. NMDA activated the receptor channel and produced currents in glial cells.

Dual effects of ATP on the potassium channel and intracellular Ca2+ release in smooth muscle cells of the bovine brain arteries.

ATP produced whole-cell potassium currents with a latency of 200 msec in cultured smooth muscle cells of bovine brain arteries. The currents were evoked via an ATP receptor linked to a pertussis toxin-insensitive G-protein, which is not involved in phospholipase C (PLC)-mediated signal transduction, and were not regulated by protein kinase A or C. In the cell-attached patches, ATP elicited single channel currents with two major classes of slope conductances and these currents were again induced within 100 msec after bath-application of ATP outside the patch pipette.

ATP activates the potassium channel and enhances cytosolic Ca2+ release via a P2Y purinoceptor linked to pertussis toxin-insensitive G-protein in brain artery endothelial cells.

ATP produced whole-cell potassium currents in cultured endothelial cells of the bovine brain cortical arteries. P2 purinoceptor agonists evoked similar currents with the order of their potency: 2-methylthio ATP > ATP >> alpha, beta-methylene ATP > or = UTP > or = ADP >> AMP. ATP-evoked currents were inhibited by GDP beta S, but not by pertussis toxin (PTX).

Adenosine activates the potassium channel via a P2 purinoceptor but not via an adenosine receptor in cultured rat superior colliculus neurons.

The effect of adenosine on superior colliculus neurons was examined by whole-cell patch clamp recording. Adenosine elicited whole-cell potassium currents. A selective A1 or A2a adenosine receptor agonist induced no current and furthermore, adenosine-evoked currents were not inhibited by selective A1 or A2a adenosine receptor antagonists or a non-selective adenosine receptor (P1 purinoceptor) antagonist, indicating that the currents are not mediated by adenosine receptors.

A P2 purinoceptor activated by ADP in rat medullar neurons.

ADP evoked outwardly rectifying potassium currents with a latency of 0.6 s in cultured rat medullar neurons. Purinoceptor agonists, such as 2-methylthio ATP (2-MeSATP), ATP, AMP, alpha,beta-methylene ATP (alpha,beta-MeATP), and UTP, produced similar outward currents with the order of their potencies for current amplitudes: 2-MeSATP > ADP > ATP > or = alpha,beta-MeATP > or = AMP > UTP.

The P2Y purinoceptor-operated potassium channel is possibly regulated by the beta gamma subunits of a pertussis toxin-insensitive G-protein in cultured rat inferior colliculus neurons.

In whole-cell patches of inferior colliculus neurons, ADP evoked outwardly rectifying potassium currents with a latency of < 1 sec via P2Y purinoceptor. These currents were blocked by GDP beta S, while not by pertussis toxin (PTX). Additionally, a selective protein kinase C inhibitor, GF109203X, or a selective phospholipase A2 inhibitor, BPB, had no effect on the currents.

Activation of endogenous protein kinase C enhances currents through alpha 1 and alpha 2 glycine receptor channels.

The effects of Ca2+ /phospholipid dependent (PKC) phosphorylation on the current amplitudes of alpha 1 and alpha 2 glycine receptors expressed in Xenopus oocytes were examined by whole cell voltage clamp recording. In studies using phorbol esters, PKC phosphorylation has been shown to reduce glycine-induced currents. Endogenous PKC activation by pretreatment with serum, however, enhanced the currents to around 140% in both alpha 1 and alpha 2 glycine receptors.

Methylcobalamin induces a long-lasting enhancement of the postsynaptic field potential in hippocampal slices of the guinea pig.

Methylcobalamin (CH3-B12) enhanced postsynaptic field potential (PSP) elicited from hippocampal slices (around 180% at a maximum), lasting more than 1 h after washing out, while it had no effect on antidromic spike potential (AP). By contrast, cyanocobalamin containing CN- instead of CH3- showed no enhancement in the PSP amplitude, suggesting that CH3- plays an important role for the PSP enhancement by methylcobalamin. The treatment with N-methyl-D-aspartate (NMDA) receptor specific antagonist, DL-2-amino-5-phosphonovaleric acid (APV) inhibited methylcobalamin-induced PSP enhancement by 50%, suggesting that NMDA receptor is partially relevant to the formation of this enhancement.

ATP-evoked potassium currents in rat striatal neurons are mediated by a P2 purinergic receptor.

The effect of ATP on cultured striatal neurons was examined by whole cell voltage clamp recordings. ATP produced outwardly rectifying currents that reversed near the expected equilibrium potential for the potassium ion and the currents were blocked by intracellular Cs+. Purinergic receptor agonists such as ADP, AMP adenosine, and 2-methylthio ATP (2-MeSATP) also evoked similar outward currents.

Cleavage of connectin by calpain and cathepsin D.

mu-Calpain quickly split the alpha-connectin in myofibrils into beta-connectin, and then produced a 1700-kDa component. Cathepsin D also split alpha-connectin into beta-connectin, further degrading it to fragments smaller than the 1700-kDa component with increasing incubation time. The action of cathepsin D on the connectin molecule was distinctly different from that of mu-calpain in terms of the splitting rate and manner.

Effects of high pressure treatment on Ca2+ release and Ca2+ uptake of sarcoplasmic reticulum.

To clarify the mechanism of pressure-induced meat tenderization or acceleration of meat conditioning, the pressure-induced morphological and biochemical changes in sarcoplasmic reticulum (SR), and Ca2+ release from SR in the rabbit skeletal muscle treated with high pressure (100-300 MPa, 5 min) were investigated in comparison with those of the SR from conditioned muscle. The destruction of the membrane structure of the SR expanded with increasing pressure applied to the muscle. Significant changes in the SDS-PAGE profile were not observed in the SR from the pressurized muscle up to 200 MPa, but a marked decrease of the ATPase protein and high-affinity Ca(2+)-binding protein were observed in the SR from the pressurized muscle at 300 MPa.

Levels of calpain and calpastatin in meat subjected to high pressure.

The levels of μ-, m-calpain and calpastatin were assayed in pressurized rabbit muscle. The crude calpain level from the pressurized muscle at 100 MPa was almost the same with that of control. Above 100 MPa, the level of calpain decreased rapidly with increased pressure.

Toluene inhibits synaptic transmission without causing gross morphological disturbances.

The effects of toluene on synaptic transmission and neuronal morphology were investigated using guinea pig hippocampal slices. Population spikes (PS) were elicited in granule cell layer by stimulation of the perforant path and antidromic potentials (AP) were evoked in the same locii by stimulation of mossy fibers. Toluene at a concentration of 1000 micrograms/ml completely depressed post-synaptic responses within 15 min but increased the AP to 140% of its original value.

The contribution of PKA to the excitatory mechanism of adenosine in guinea pig superior colliculus slices.

The involvement of cyclic AMP-dependent protein kinase (PKA) for excitatory action of adenosine on neurotransmission was investigated using superior colliculus slices. The postsynaptic potential was elicited in the superficial gray layer after optic layer stimulation. Application of dibutyryl cyclic AMP to the medium enhanced the postsynaptic potential, but additional application of adenosine at 100 microM did not change the amplitude.

Effects of high pressure treatment on the proteolytic enzymes in meat.

This paper describes the effects of high-pressure treatment on proteolytic enzymes in muscle, especially catheptic enzymes which influence meat tenderization, and on acid phosphatase, used as an index of disruption of lysosomal membranes. Acid phosphatase activity in the extract from pressurized muscle increased with increasing pressure applied to the muscle up to 500 MPa. Activity of cathepsin B, D and L increased up to 400 MPa, then tended to decrease at 500 MPa.

Effects of high pressure treatment on the flavour-related components in meat.

This paper describes the effects of high-pressure treatment on the water-soluble components of meat responsible for the flavor of meat. The amounts of peptides and amino acids as estimated by phenol reagent positive materials (PPM) apparently increased with increasing pressure applied to the muscle up to 300 MPa, but the differences between each treatment were not statistically significant. When the muscles were stored at 2°C for 7 days after the pressurization, increases in the amount of PPM were observed both in untreated and pressurized muscles.

Effects of calf breed on milk production and other economic traits of Holstein dams.

Production of purebred or crossbred feeder calves for beef, especially HolsteinxJapanese-Black (HxJB) and Japanese-Black (JB), from dairy cattle using artificial insemination or embryo transfer have been used widely in Japan. However, dairy farmers feel uneasy about the effects of calf breed on the economic traits of dams. In this study, those effects were investigated in 798 Holstein heifers bearing Holstein, HxJB, JB or other breed calves.