香茶菜甲素酯对依赖钙调素的环核苷酸磷酸二酯酶的抑制作用

香茶菜甲素酯是香茶菜甲素的一种新的衍生物。研究发现该化合物能明显抑制CaM激活的PDE活性,其IC_(50)为75μmol/L。抑制动力学测定表明它以非竞争方式拮抗CaM对PDE的活化。CaM荧光测定显示,香茶菜甲素酯可以降低ca~(2+)诱导的CaM酪氨酸荧光强度,提示它可能通过改变Ca~(2+)—CaM构象而抑制CaM—PDE。     

Involvement of calmodulin in platelet reaction

Penothiazines, known as selective inhibitors of calmodulin, completely inhibited platelet aggregation and secretion induced by ADP, collagen, epinephrine, thrombin or calcium ionophore. They also completely inhibited aggregation induced by exogenous arachidonate (AA) or a mixture of thromboxane A₂ and prostaglandin endoperoxides (TxA₂/PG G₂,H₂). Also, in the presence of these calmodulin inhibitors, the release of AA from platelet phospholipids (PL) was dosedependently inhibited in stimulated platelets. These observations suggest that in platelet reaction, calmodulin is involved in at least two different steps of the reaction: activation of phospholipases and contraction of platelet actomyosin after the formation of TxA₂.     

Topical W-7 inhibits ultraviolet radiation-induced melanogenesis in Skh:HR2 pigmented hairless mice

We studied the effect of N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide (W-7) on ultraviolet radiation (UVR)-induced melanogenesis (tanning) in Skh:HR2 pigmented hairless mice. Topically pretreated mice were exposed to subminimal edematogenic as well as edematogenic UVR doses to establish whether W-7-UVR-induced edema prophylaxis allows increased melanogenesis while preventing edema. Ultraviolet light-irradiated vehicle control animals developed visible tans; however, both W-7-treated groups failed to tan. Topical W-7 before UVR exposure inhibited UVR induction of dopa oxidase activity in melanocytes by 49% (P=0.029) and inhibited UVR-induced deposition of melanin in the epidermis by 88% (P=0.006). Topical W-7 blocked 23% of the UVR but this blockage could not account for the inhibition of dopa oxidase and melanization. We conclude that, in addition to preventing edema, W-7 inhibits UVR-induced melanogenesis, possibly by affecting Ca²⁺-calmodulin and/or protein kinase C-dependent processes.     

Protein kinases modulate the sensitivity of hippocampal neurons to nitric oxide toxicity and anoxia

Multiple processes lead to neuronal death after ischemia, but the generation of nitric oxide (NO) is a key component in this cascade of events. The mechanisms that regulate the extent of neuronal degeneration during anoxia and NO toxicity are multifactorial. Neuronal death may be modulated by the activity of signal transduction systems that influence the toxicity of NO or its metabolic products such as cGMP. The enzyme responsible for the production of NO, nitric oxide synthase (NOS), is phosphorylated by protein kinase C (PKC), the cAMP-dependent protein kinase (PKA), and the calcium/calmodulin-dependent protein kinase II (CaM-II). We examined in primary cultured hippocampal neurons whether the protein kinases PKC, PKA, CaM-II, and cGMP-dependent protein kinase modified the toxic effects of anoxia and NO. Down-regulation of PKC activity with PMA (1μM) increased hippocampal neuronal survival during anoxia and NO exposure from approximately 22% to 88%. Inhibitors of PKC activity 9H-7, H-8, sphingosine, and staurosporine also were neuroprotective. Down-regulation of PKC activity increased survival during anoxia even in the presence of the NOS inhibitor, N^ω-methyl-L-arginine. Thus, although down-regulation of PKC activity may increase neuronal survival by decreasing NOS activity, it also is likely that PKC contributes to ischemic neuronal death by mechanisms that are independent of NOS. Inhibition of the cGMP-dependent protein kinase activity, but not the activity of the CaM-II also was neuroprotective during NO administration. In contrast to the protective effects of inhibition of PKC and the cGMP-dependent protein kinase, activation rather than inhibition of PKA increased hippocampal neuronal survival during NO exposure. These results indicate that neuronal survival during anoxia and NO exposure is linked to the modulation of PKC, PKA, and cGMP-dependent protein kinase activity but is not dependent on the CaM-II pathway. Understanding the involvement of PKC, PKA, and the cGMP-dependent protein kinase in modulating the effect of neuronal death during ischemia and NO toxicity may help in directing future therapeutic modalities for cerebrovascular disease. © 1993 Wiley-Liss, Inc.     

阿片类物质对淋巴细胞内环磷酸腺苷及游离钙的影响

文本观察了几种阿片类物质对小鼠脾脏淋巴细胞内环磷酸腺苷,游离钙及钙调蛋白的影响。结果表明:吗啡、α-CAO、MENK、DADLE及强啡肽均降低小鼠脾脏淋巴细胞内环磷酸腺苷水平,升高淋巴细胞内游离钙浓度,增加淋巴细胞内钙调蛋白活性。预先给予纳洛酮能够阻断阿片类物质的作用。说明阿片类物质的作用是通过阿片受体介导的。     

Central nicotinic acetylcholine receptor involved in Ca(2+) -calmodulin-endothelial nitric oxide synthase pathway modulated hypotensive effects

BACKGROUND AND PURPOSE

Recent evidence has suggested that nicotine decreases blood pressure (BP) and heart rate (HR) in the nucleus tractus solitarii (NTS), indicating that nicotinic acetylcholine receptors (nAChRs) play an important role in BP control in the NTS. However, the signalling mechanisms involved in nAChR-mediated depressor effects in the NTS are unclear. Hence, the aim of this study was to investigate these signalling mechanisms.

EXPERIMENTAL APPROACH

Depressor responses to nicotine microinjected into the NTS of Wistar-Kyoto rats were elicited in the absence and presence of an antagonist of α7 nAChR, the calcium chelator ethylene glycol tetraacetic acid, a calmodulin-specific inhibitor, nitric oxide (NO) synthase (NOS) inhibitor, endothelial NOS (eNOS)-selective inhibitor or neuronal NOS (nNOS)-specific inhibitor.

KEY RESULTS

Microinjection of nicotine into the NTS produced a dose-dependent decrease in BP and HR, and increased nitrate levels. This depressor effect of nicotine was attenuated after pretreatment with a nAChR antagonist or blockers of the calmodulin-eNOS pathway. In contrast, N5-(1-Imino-3-butenyl)-L-ornithine (vinyl-L-NIO), nNOS-specific inhibitor, did not diminish these nicotine-mediated effects. Calmodulin was found to bind eNOS after nicotine injection into NTS. However, nicotine did not affect the eNOS phosphorylation level or eNOS upstream extracellular signal-regulated kinases (ERK)1/2 and Akt phosphorylation levels. Furthermore, pretreatment with an ERK1/2 or Akt inhibitor did not attenuate nicotine-induced depressor effects in the NTS.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the nAChR-Ca²⁺-calmodulin-eNOS-NO signalling pathway, but not nNOS, plays a significant role in central BP regulation, and neither the ERK1/2 nor Akt signalling pathway are significantly involved in the activation of eNOS by nAChRs in the NTS.     

Cardiac ischaemic stress: cardiomyocyte Ca²⁺, sex and sex steroids

1. Important sex differences exist in ischaemic heart disease. Oestrogen has been conventionally regarded as providing a cardioprotective benefit and testosterone frequently perceived to exert a deleterious effect. However, there is accumulating evidence that argues against this simple dichotomy, suggesting that the influence of oestrogen and testosterone conferring benefit or detriment may be context specific. 2. Cardiomyocyte calcium (Ca(2+)) loading is recognized to be a major factor in acute ischaemia-reperfusion pathology, promoting cell death, contractile dysfunction and arrhythmogenic activity. Ca(2+)/calmodulin-dependent kinase II (CaMKII) is a mediator of many of the cardiomyocyte Ca(2+)-related pathologies in ischaemia-reperfusion. Cardiomyocyte Ca(2+)-handling processes have been shown to be modulated by the actions of oestrogen and testosterone. A role for these sex steroids in influencing CaMKII activation is argued. 3. Although many experimental studies of oestrogen manipulation can identify a cardioprotective role for this sex steroid, there are also numerous reports that fail to demonstrate sex differences in postischaemic recovery. Experimental studies report that testosterone can be protective in ischaemia-reperfusion in males and females in some settings. 4. Further studies of sex steroid influence in the ischaemic heart will allow the development of therapeutic interventions that are specifically targeted for male and female hearts.