Phorbol 12,13-diacetate-induced contraction of the canine basilar artery: role of protein kinase C.

The pharmacological and biochemical mechanisms of contractile responses to the protein kinase C (PKC) activator phorbol-12,13-diacetate (PDA) were investigated in canine basilar arteries. In the normal medium, PDA elicited a strong, dose-related, and slow-developing sustained contraction. Among the constrictors examined, including serotonin, prostaglandin F2 alpha, and endothelin, only PDA yielded contractions in a Ca2(+)-free medium. In both media, the PDA-induced contractions were virtually inhibited by either staurosporine, H-7, or quinacrine, while neither neurotransmitter blockades nor R24571 (calmidazolium) exerted significant effects. In addition, it was shown that 8-bromocyclic GMP, but not 8-bromocyclic AMP, markedly curtailed the PDA-induced contractions. Biochemical analysis, furthermore, showed that PDA induced increased phosphorylations of 27- and 96-kDa and proteins other than the myosin light chain (MLC) 20-kDa protein. Thus, the present results open up a novel mechanism of sustained cerebral artery contractions, where PKC activation rather than Ca2+/calmodulin/MLC system plays a key role that is regulated both by phospholipase A2 and by cyclic GMP.

Intracellular marking with lucifer yellow CH and horseradish peroxidase of cells electrophysiologically characterized as glia in the cerebral cortex of the cat.

Intracellular microelectrodes filled with either Lucifer Yellow CH, a highly florescent dye, or horseradish peroxidase (HRP) were used to electrophysiologically characterize and mark cells in the cerebral cortex of cat. Fifty-eight cells, characterized electrophysiologically as glia, were marked with Lucifer Yellow CH. All were identified as protoplasmic astrocytes, and included cells in the glia limitans of the molecular layer. An additional 54 cells, similarly characterized as glia, were labeled with HRP. The results were the same; only protoplasmic astrocytes were labeled. The "staining quality" of the glia labeled with HRP was superior to that of cells injected with Lucifer Yellow; greater lengths of individual processes were revealed, and they could often be followed to blood vessels where they ended on the walls of vessels with expanded perivascular end-feet. The observations indicate that the many previously reported studies on presumed glial cells in the cat cerebral cortex have characterized the behavior of protoplasmic astrocytes. Neurons were also marked during these experiments. The "staining" quality of the Lucifer Yellow filled neurons was excellent; dendritic spines, axons, and axon collaterals were clearly visible. These fine neuronal details were not as well revealed after HRP labeling. High resting membrane potentials (RMP's) were not a prerequisite for obtaining well-marked neurons (mean RMP of Lucifer Yellow filled neurons was -33.6 mV; mean RMP of HRP filled neurons was 42.3 mV). In contrast, the mean RMPs of Lucifer Yellow and HRP marked glia was -68 Mv and -75 mV respectively, and the quality of "staining" appeared to be more closely related to the RMP.

Neurochemical correlates of selective neuronal loss following cerebral ischemia: role of decreased Na+,K(+)-ATPase activity.

In order to investigate the role of Na+,K(+)-ATPase in the development of neuronal necrosis following cerebral ischemia, ischemia was induced in gerbils by occluding the common carotid artery unilaterally for 10 min. A time-course analysis revealed that significant reductions of the Na+,K(+)-ATPase activity in the cerebral cortex and hippocampus were manifested at 15 min, 30 min, and 1 h, and returned to the control level one day following recirculation. No apparent alterations of the Mg(2+)-ATPase activity, on the other hand, were obtained throughout the experimental period. Furthermore, Scatchard analyses of [3H]ouabain binding to the cerebral cortex membranes disclosed that the Bmax values invariably decreased without any change of Kd values following ischemia. It has also been shown that treatment of the animals with an agent known to mitigate ischemic neuronal necrosis, i.e. BY-1949, significantly reversed such derangements. These results suggest that the recovery of decreased Na+,K(+)-ATPase activity shortly after ischemia exerts a protective effect against ischemic brain damage.

BY-1949 elicits vasodilation via preferential elevation of cyclic GMP levels within the cerebral artery: possible involvement of endothelium-mediated mechanisms.

The pharmacological mechanisms by which BY-1949, a novel dibenzoxazepine derivative, increases in regional cerebral blood flow, were investigated using the canine basilar artery in vitro. BY-1949 inhibited contractions elicited by serotonin (5-HT), prostaglandin (PG) F2 alpha, endothelin and phorbol-12,13-diacetate (PDA), respectively, to the same extent. In addition, pretreatment of the artery with methylene blue significantly suppressed the vasodilating effect of BY-1949. BY-1949 also dose dependently suppressed contractions of the basilar artery induced by CaCl2 (Ca2+) in a non-competitive manner. Biochemical studies disclosed that BY-1949 significantly increased cyclic GMP without causing any apparent change in cyclic AMP. These increases in cyclic GMP were virtually abolished after the endothelial cells were removed. These results strongly suggest that the increased regional cerebral blood flow induced by BY-1949 is explicable, at least partly, in terms of a preferential elevation of cyclic GMP within the cerebral vasculature, where the endothelium plays a pivotal role.

The role of cGMP in the anti-aggregating properties of BY-1949, a novel dibenzoxazepine derivative.

The anti-aggregatory activity of a novel agent, BY-1949, 3-methoxy-11-methyldibenz (b,f) (1,4) oxazepine-8-carboxylic acid, was examined using rabbit platelets. Oral administration of BY-1949 (10 or 30 mg/kg) inhibited platelet aggregation induced by ADP, collagen, and arachidonate in a dose-related fashion. In in vitro studies, however, neither BY-1949 nor its major metabolites inhibited platelet aggregation, even at a concentration similar to that attained in plasma in vivo. With regard to the anti-aggregatory action of BY-1949, biochemical analysis revealed that BY-1949 preferentially augmented cyclic GMP (cGMP) formation, via inhibition of phosphodiesterase activity, without altering cyclic AMP (cAMP) formation. Furthermore, the in vitro anti-aggregatory activity was significantly enhanced when the platelets were concomitantly treated with nitric oxide (NO). Based on these results, it is suggested that the in vivo anti-aggregatory effects of BY-1949 are at least partly elicited via platelet/endothelium interactions, in which cGMP plays a pivotal role.

A novel dibenzoxazepine derivative (BY-1949) increases regional cerebral blood flow.

The effects of BY-1949, a novel dibenzoxazepine derivative, on the regional cerebral blood flow were investigated in conscious cats. Oral administration of BY-1949 (10-50 mg/kg) significantly increased in a dose-related manner the regional cerebral blood flow in all brain regions examined. Vinpocetine (20 mg/kg p.p.) had similar effects that were shorter-lasted than those of BY-1949. From these results, it seems likely that amelioration by BY-1949 of cognitive impairment following cerebral ischemia/hypoxia or that occurs on ageing is at least partly explainable in terms of its effects on the cerebral circulation.

Neuronal and glial activity during spreading depression in cerebral cortex of cat.

1. Extra- and intracellular potentials were recorded from neurons and glia during spreading depression (SD) in cerebral cortex of cats. The glial membrane depolarized during SD and the time course of depolarization was concurrent with the surface DC change of SD. The glial depolarization evoked by 20-Hz repetitive cortical stimulation disappeared during the negative DC shift of SD. Simultaneous recording of the extra- and intracellular potentials from a single glial cell with a coaxial microelectrode showed that the extracellular DC potential change was of opposite polarity to the glial intracellular potential, which suggests that the slow glial depolarization concurrent with SD is not the field potential. In contrast to glial cells, the neuronal burst discharges as well as the neuronal membrane depolarization associated with SD did not show a close relationship to SD: the neuronal membrane depolarization and discharge were frequently delayed by 10-3- s from the onset of the SD slow wave. Sometimes SD was observed without accompanying neuronal depolarization. The degree of neuronal depolarization was not always correlated with the amplitude of the negative wave of SD. 2. The effect of tetrodotoxin (TTX) on the negative DC potential of SD was examined. Simultaneous recording of glial membrane potential and the neuronal unit activity as well as extracellular DC potential and surface DC potential during SD was performed and the TTX-treated cortex was compared with the normal state. TTX did not change the DC level of the cerebral cortex. SD could be evoked by KCl when neuronal discharge was completely abolished by TTX application...

An activation of synaptosomal Na+,K(+)-ATPase by a novel dibenzoxazepine derivative (BY-1949) in the rat brain: its functional role in the neurotransmitter uptake systems.

In search of factors mitigating the final outcome of ischemic and epileptic brain damage, we tested a novel dibenzoxazepine derivative (BY-1949), as the compound has been shown to be effective under these two conditions. First, using rat brain, we assessed whether or not BY-1949 affects the Na+,K(+)-ATPase activity. Although in vitro applications of either BY-1949 or its three major metabolites did not cause any apparent effects, both acute and chronic oral administrations of the compound (10 mg/kg) invariably increased the Na+,K(+)-ATPase activity in the synaptosomal plasma membranes by increasing Vmax values. Second, it was shown by this study that the drug treatment caused marked increases in the uptake of both glutamic acid and gamma-aminobutyric acid into the synaptosomes. These results suggest that the activity against ischemic/epileptic brain damage by BY-1949 is explicable, at least partly, in terms of improvement of ionic derangements across the neural membranes via Na+,K(+)-ATPase activation.

Possible mechanisms of 15-hydroperoxyarachidonic acid-induced contraction of the canine basilar artery in vitro.

Pharmacological studies of the contraction induced by 15-hydroperoxyarachidonic acid (15-HPAA) were done in the isolated canine basilar artery. The maximal contractile force produced by 15-HPAA was 1.5 times that of serotonin and was equivalent to that of prostaglandin (PG) F2 alpha or PGA1. At concentrations in which reductions of [14C]-6-keto-PGF1 alpha (the breakdown product of PGI2) occurred, both 15-HPAA and tranylcypromine contracted the artery, whereas indomethacin consistently relaxed it. In the case of indomethacin, as the drug inhibited the synthesis of [14C]-PGE2, F2 alpha and thromboxane(TX) B2 (the breakdown product of TXA2) as well, it has been considered that the balances between PGI2 and other vasoconstrictive PGs or TX may regulate the tone of the artery. Furthermore, it was shown that 15-HPAA enhanced the synthesis of lipoxygenase products from [14C]arachidonic acid. Experiments were done, therefore, to know whether these enhanced lipoxygenase products participated in the manifestation of contraction induced by 15-HPAA or not. As a result, although indomethacin did not affect the contraction, significant reductions of the contraction were shown by eicosatetraynoic acid. These results suggest that enhanced synthesis of lipoxygenase products may be involved in eliciting contractile responses of 15-HPAA.