Na+ entry via TRPC6 causes Ca2+ entry via NCX reversal in ATP stimulated smooth muscle cells

Reversal of the Na+/Ca2+ -exchanger (NCX) has been shown to mediate Ca2+ influx during activation of G-protein linked receptors. Functional coupling between the reverse-mode NCX and the canonical transient receptor potential channels (TRPCs) has been proposed to mediate Ca2+ influx in HEK-293 cells overexpressing TRPC3. In this communication we present evidence for similar functional coupling of NCX to endogenously expressed TRPC6 in rat aorta smooth muscle cells. Selective inhibition of reverse-mode NCX with KB-R7943 and of non-selective cation-channels with SKF-96365 abolished Ca2+ influx in response to agonist stimulation (ATP). Expression of a dominant negative TRPC6 mutant also reduced the Ca2+ influx in proportion to its transfection efficiency. Calyculin A, which is known to disrupt the junctions of the plasma membrane and sarco/endoplasmic reticulum, increased global Na+ elevations and reduced stimulated Ca2+ influx. Together our data provide evidence that localized Na+ elevations are generated by TRPC6 and drive reversal of NCX to mediate Ca2+ influx.

Key role of Kv1 channels in vasoregulation

Small arteries play an essential role in the regulation of blood pressure and organ-specific blood flow by contracting in response to increased intraluminal pressure, ie, the myogenic response. The molecular basis of the myogenic response remains to be defined. To achieve incremental changes in arterial diameter, as well as blood pressure or organ-specific blood flow, the depolarizing influence of intravascular pressure on vascular smooth muscle membrane potential that elicits myogenic contraction must be precisely controlled by an opposing hyperpolarizing influence. Here we use a dominant-negative molecular strategy and pressure myography to determine the role of voltage-dependent Kv1 potassium channels in vasoregulation, specifically, whether they act as a negative-feedback control mechanism of the myogenic response. Functional Kv1 channel expression was altered by transfection of endothelium-denuded rat middle cerebral arteries with cDNAs encoding c-myc epitope-tagged, dominant-negative mutant or wild-type rabbit Kv1.5 subunits. Expression of mutant Kv1.5 dramatically enhanced, whereas wild-type subunit expression markedly suppressed, the myogenic response over a wide range of intraluminal pressures. These effects on arterial diameter were associated with enhanced and reduced myogenic depolarization by mutant and wild-type Kv1.5 subunit expression, respectively. Expression of myc-tagged mutant and wild-type Kv1.5 subunit message and protein in transfected but not control arteries was confirmed, and isolated myocytes of transfected but not control arteries exhibited anti-c-myc immunofluorescence. No changes in message encoding other known, non-Kv1 elements of the myogenic response were apparent. These findings provide the first molecular evidence that Kv1-containing delayed rectifier K+ (K(DR)) channels are of fundamental importance for control of arterial diameter and, thereby, peripheral vascular resistance, blood pressure, and organ-specific blood flow.

Essential role of nuclear medicine technology in tositumomab and 131I-tositumomab therapeutic regimen for non-Hodgkin's lymphoma

Nuclear medicine technology has traditionally focused on diagnostic imaging, with therapeutics left mostly to other medical disciplines. However, after many years in development, radioimmunotherapy (RIT) has finally become a clinical reality in many nuclear medicine departments. The nuclear medicine technologist is a key player in the successful implementation of RIT. Delivery of a therapeutic regimen of tositumomab and (131)I-tositumomab provides a model for the technologist's roles and responsibilities in the developing field of RIT. This article examines the clinical rationale, logistic requirements, and imaging and dosimetry procedures required by this treatment regimen. Upon completion of this article, the reader should be able to describe the target patient population and identify the roles and responsibilities of various members of the treatment team. The reader will also gain an understanding of the treatment process, including drug administration, imaging, and therapeutic dose calculations.

Heteromultimeric TRPC6-TRPC7 channels contribute to arginine vasopressin-induced cation current of A7r5 vascular smooth muscle cells

The molecular identity of receptor-operated, nonselective cation channels (ROCs) of vascular smooth muscle (VSM) cells is not known for certain. Mammalian homologues of the Drosophila canonical transient receptor potential channels (TRPCs) are possible candidates. This study tested the hypothesis that heteromultimeric TRPC channels contribute to ROC current of A7r5 VSM cells activated by [Arg(8)]-vasopressin. A7r5 cells expressed transcripts encoding TRPC1, TRPC4beta, TRPC6, and TRPC7. TRPC4, TRPC6, and TRPC7 protein expression was confirmed by immunoblotting and association of TRPC6 with TRPC7, but not TRPC4beta, was detected by coimmunoprecipitation. The amplitude of arginine vasopressin (AVP)-induced ROC current was suppressed by dominant-negative mutant TRPC6 (TRPC6(DN)) but not TRPC5 (TRPC5(DN)) mutant subunit expression. These data indicate a role for TRPC6- and/or TRPC7-containing channels and rule a more complex subunit composition including TRPC1 and TRPC4. Increasing extracellular Ca(2+) concentration ([Ca(2+)](o)) from 0.05 to 1 mmol/L suppressed currents owing to native, TRPC7, and heteromultimeric TRPC6-TRPC7 channels, but not TRPC6 current, which was slightly enhanced. The relative changes in native and heteromultimeric TRPC6-TRPC7 current amplitudes for [Ca(2+)](o) between approximately 0.01 and 1 mmol/L were identical, but the changes in homomultimeric TRPC6 and TRPC7 currents were significantly less and greater, respectively, compared with the native channels. Taken together, the data provide biochemical and functional evidence supporting the view that heteromultimeric TRPC6-TRPC7 channels contribute to receptor-activated, nonselective cation channels of A7r5 VSM cells.

Myogenic regulation of arterial diameter: role of potassium channels with a focus on delayed rectifier potassium current

The phenomenon of myogenic constriction of arterial resistance vessels in response to increased intraluminal pressure has been known for over 100 years, yet our understanding of the molecular mechanisms involved remains incomplete. The focus of this paper concerns the potassium (K+) channels that provide a negative feedback control of the myogenic depolarization of vascular smooth muscle cells that is provoked by elevations in intraluminal pressure, and specifically, the contribution of delayed rectifier (KDR) channels. Our knowledge of the important role played by KDR channels, as well as their molecular identity and acute modulation via changes in gating, has increased dramatically in recent years. Several lines of evidence point to a crucial contribution by heteromultimeric KV1 subunit-containing KDR channels in the control of arterial diameter and myogenic reactivity, but other members of the KV superfamily are also expressed by vascular myocytes, and less is known concerning their specific functions. The effect of pharmacological modulation of KDR channels is discussed, with particular reference to the actions of anorexinogens on KV1- and KV2-containing KDR channels. Finally, the need for a greater understanding of the mechanisms that control KDR channel gene expression is stressed in light of evidence indicating that there is a reduced expression of KDR channels in diseases associated with abnormal myogenic reactivity and vascular remodelling.Key words: resistance arteries, myogenic response, potassium channels, delayed rectifier K+ current, KV channels, KV1, KV2.

Defects in cAMP-pathway may initiate carcinogenesis in dividing nerve cells: a review

The mechanisms of carcinogenesis in nervous tissues are not well understood. It is now established that adenosine 3,',5'-cyclic monophosphate (cAMP)-pathway plays a crucial role in initiating differentiation in transformed and embryonic cells of neuronal and glial origin. Therefore, we propose that defects in the cAMP-pathway may initiate the first phase of carcinogenesis (immortalization). Subsequent genetic abnormalities in oncogenes, anti-oncogenes or other cellular genes individually or in combination may lead to transformation (cancer phenotype). This hypothesis is derived from the fact that an elevation of the cAMP level in murine NB cells induces terminal differentiation in many of these cells in spite of the fact that they are highly aneuploid. Additional changes in cAMP-regulated genes responsible for initiating differentiation may make these cells resistant to cAMP or may make the cAMP-effect on differentiation reversible. Indeed, cAMP-resistant cells exist in NB cell populations, and the cAMP-effect on differentiation is reversible in glioma cells. Identification of genes that initiate, promote and maintain terminal differentiation and those which prevent differentiation following elevation of cAMP in NB cells may increase our understanding of the mechanisms of carcinogenesis. This review illustrates the following: (a) historical background leading to the discovery of cAMP as an inducer of differentiation in nerve cells; (b) identification of potential sites in cAMP-pathway that may play a crucial role in initiating the first phase of carcinogenesis (immortalization) and potential gene targets in immortalized cells whose alterations may cause neoplastic transformation of nerve cells. It is interesting to note that the cAMP pathway remains responsive to an elevated cAMP level in inducing differentiation in NB cells in spite of chromosomal anomalies and genetic changes associated with the maintenance of a cancer phenotype.

Alpha-tocopheryl succinate, the most effective form of vitamin E for adjuvant cancer treatment: a review

In 1982, it was established that alpha-tocopheryl succinate (alpha-TS) was the most effective form of vitamin E in comparison to alpha-tocopherol, alpha-tocopheryl acetate and alpha-tocopheryl nicotinate in inducing differentiation, inhibition of proliferation and apoptosis in cancer cells, depending upon its concentration. During the last two decades, several studies have confirmed this observation in rodent and human cancer cells in culture and in vivo (animal model). The most exciting aspect of this alpha-TS effect is that it does not affect the proliferation of most normal cells. In spite of several studies published on the anti-cancer properties of alpha-TS, the value of this form of vitamin E has not drawn significant attention from researchers and clinicians. Therefore, a critical review on the potential role of alpha-TS in the management of cancer is needed. In addition, such a review can also provide in-depth analysis of existing literature on this subject. alpha-TS treatment causes extensive alterations in gene expression; however, only some can be attributed to differentiation, inhibition of proliferation and apoptosis. alpha-TS also enhances the growth-inhibitory effect of ionizing radiation, hyperthermia, some chemotherapeutic agents and biological response modifiers on tumor cells, while protecting normal cells against some of their adverse effects. Thus, alpha-TS alone or in combination with dietary micronutrients can be useful as an adjunct to standard cancer therapy by increasing tumor response and possibly decreasing some of the toxicities to normal cells.

ATP-sensitive K+ channels of vascular smooth muscle cells

ATP-sensitive potassium channels (K(ATP)) of vascular smooth muscle cells represent potential therapeutic targets for control of abnormal vascular contractility. The biophysical properties, regulation and pharmacology of these channels have received intense scrutiny during the past twenty years, however, the molecular basis of vascular K(ATP) channels remains ill-defined. This review summarizes the recent advancements made in our understanding of the molecular composition of vascular K(ATP) channels with a focus on the evidence that hetero-octameric complexes of Kir6.1 and SUR2B subunits constitute the vascular K(ATP) subtype responsible for control of arterial diameter by vasoactive agonists.

Smooth muscle membrane potential modulates endothelium-dependent relaxation of rat basilar artery via myo-endothelial gap junctions

The release of endothelium-derived relaxing factors, such as nitric oxide (NO), is dependent on an increase in intracellular calcium levels ([Ca(2+)](i)) within endothelial cells. Endothelial cell membrane potential plays a critical role in the regulation of [Ca(2+)](i) in that calcium influx from the extracellular space is dependent on membrane hyperpolarization. In this study, the effect of inhibition of vascular smooth muscle delayed rectifier K(+) (K(DR)) channels by 4-aminopyridine (4-AP) on endothelium-dependent relaxation of rat basilar artery to acetylcholine (ACh) was assessed. ACh-evoked endothelium-dependent relaxations were inhibited by N-(Omega)-nitro-L-arginine (L-NNA) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), confirming a role for NO and guanylyl cyclase. 4-AP (300 microM) also suppressed ACh-induced relaxation, with the maximal response reduced from approximately 92 to approximately 33 % (n = 11; P < 0.01). However, relaxations in response to exogenous NO, applied in the form of authentic NO, sodium nitroprusside or diethylamineNONOate (DEANONOate), were not affected by 4-AP treatment (n = 3-11). These data are not consistent with the view that 4-AP-sensitive K(DR) channels are mediators of vascular hyperpolarization and relaxation in response to endothelium-derived NO. Inhibition of ACh-evoked relaxation by 4-AP was reversed by pinacidil (0.5-1 microM; n = 5) or 18beta-glycyrrhetinic acid (18betaGA; 5 microM; n = 5), indicating that depolarization and electrical coupling of the smooth muscle to the endothelium were involved. 4-AP caused depolarization of both endothelial and vascular smooth muscle cells of isolated segments of basilar artery (mean change 11 +/- 1 and 9 +/- 2 mV, respectively; n = 15). Significantly, 18betaGA almost completely prevented the depolarization of endothelial cells (n = 6), but not smooth muscle cells (n = 6) by 4-AP. ACh-induced hyperpolarization of endothelium and smooth muscle cells was also reduced by 4-AP, but this inhibition was not observed in the combined presence of 4-AP and 18betaGA. These data indicate that 4-AP can induce an indirect inhibition of endothelium-dependent relaxation in the rat basilar artery by electrical coupling of smooth muscle membrane depolarization to the endothelium via myo-endothelial gap junctions.

Risk factors for Alzheimer's disease: role of multiple antioxidants, non-steroidal anti-inflammatory and cholinergic agents alone or in combination in prevention and treatment

The etiology of Alzheimer's disease (AD) is not well understood. Etiologic factors, chronic inflammatory reactions, oxidative and nitrosylative stresses and high cholesterol levels are thought to be important for initiating and promoting neurodegenerative changes commonly found in AD brains. Even in familial AD, oxidative stress plays an important role in the early onset of the disease. Mitochondrial damage and proteasome inhibition represent early events in the pathogenesis of AD, whereas increased processing of amyloid precursor protein (APP) to beta-amyloid (Abeta) fragments (Abeta(40) and Abeta(42)) and formation of senile plaques and neurofibrillary tangles (NFTs) represent late events. We propose a hypothesis that in idiopathic AD, epigenetic components of neurons such as mitochondria, proteasomes and post-translation protein modifications (processing of amyloid precursor protein to beta-amyloid and hyperphosphorylation of tau), rather than nuclear genes, are the primary targets for the action of diverse groups of neurotoxins. Based on epidemiologic, laboratory and limited clinical studies, we propose that a combination of non steroidal anti-inflammatory drugs (NSAIDs) and appropriate levels and types of multiple micronutrients, including antioxidants, may be more effective than the individual agents in the prevention, and they, in combination with a cholinergic agent, may be more effective in the treatment of AD than the individual agents alone. In addition, agents, which can prevent formation of plaques or dissolve these plaques may further enhance the efficacy of our proposed treatment strategy.

D-alpha-tocopheryl succinate (vitamin E) enhances radiation-induced chromosomal damage levels in human cancer cells, but reduces it in normal cells

OBJECTIVE

The purpose of this study was to measure and compare the effect of d-alpha-tocopheryl succinate (alpha-TS) in modifying radiation-induced chromosomal damage in human normal cells and cancer cells in culture.

METHODS

Three human normal fibroblast cell lines (GM2149, AG1522 and HF19) and three human cancer cell lines, cervical cancer (HeLa) and ovarian carcinoma cells (OVGI and SKOV3) were treated with alpha-TS (37.6 microM) 20 hours before 100 cGy gamma-irradiation. After 30 minutes of irradiation, colcemid was added and cells were fixed. One hundred randomly selected metaphase cells were scored for the presence of chromatid gaps and breaks. To study the cellular accumulation of alpha-TS. cells were incubated in the presence of alpha-TS (18.8 and 37.6 microM) for 24 hours, and alpha-TS was extracted with hexane using a-tocopheryl acetate as an internal standard. The levels of alpha-TS were determined by HPLC.

RESULTS

Results showed that alpha-TS induced chromosomal damage in both human cervical cancer cells and ovarian cancer cells, but not in human normal fibroblasts in culture. In addition, alpha-TS enhanced the level of radiation-induced chromosomal damage in cancer cells, but it protected normal cells against such damage. Both cancer cells and normal cells accumulated similar levels of alpha-TS, suggesting that increased sensitivity of cancer cells to alpha-TS is acquired during transformation.

CONCLUSION

The use of alpha-TS during radiation therapy may improve the efficacy of radiation therapy by enhancing tumor response and decreasing some of the toxicities on normal cells.

Mevastatin induces degeneration and decreases viability of cAMP-induced differentiated neuroblastoma cells in culture by inhibiting proteasome activity, and mevalonic acid lactone prevents these effects

Statins with a closed-ring structure (mevastatin, lovastatin, and simvastatin) and with an open-ring structure (pravastatin and fluvastatin) are widely used in the human population to manage hypercholesterolemia. These statins may have neuroprotective or neurotoxic effects, but these effects remain controversial. We have utilized adenosine 3',5'-cyclic monophosphate-induced terminally differentiated murine neuroblastoma (NB) cells in culture as an experimental model to study the effect of statins. Results showed that mevastatin induced degenerative changes and reduced the viability of differentiated NB cells by inhibiting proteasome activity. Lactacystin, an established inhibitor of proteasome, also produced similar degenerative changes in these cells. In contrast, pravastatin neither affected the degeneration and viability of differentiated NB cells nor the proteasome activity. High-performance liquid chromatography (HPLC) analysis of the extract obtained from mevastatin-treated growth medium and differentiated cells revealed that about 50% of mevastatin is converted to an open-ring structure in the growth medium; however, differentiated cells did not convert any portion of mevastatin into an open-ring structure and accumulated only mevastatin with a closed-ring structure. Mevalonic acid lactone by itself did not affect the viability of differentiated NB cells or the proteasome activity, but it completely prevented mevastatin-induced degeneration and decreased viability by reducing the uptake of mevastatin and by blocking its action on proteasome activity. Mevalonic acid failed to prevent lactacystin-induced degeneration and inhibition of proteasome activity. Our results suggest that mevastatin could act as a neurotoxic agent or neuroprotective agent, depending upon the extent of its hydrolysis to an open-ring structure and the level of mevalonic acid.

Protein kinase C modulation of recombinant ATP-sensitive K(+) channels composed of Kir6.1 and/or Kir6.2 expressed with SUR2B

The molecular identity of smooth muscle ATP-sensitive K(+) channels (K(ATP)) is not established with certainty. Patch clamp methods were employed to determine if recombinant K(ATP) channels composed of Kir6.1 and SUR2B subunits expressed by human embryonic kidney (HEK293) cells share an identical modulation by protein kinase C (PKC) with the vascular K(NDP) subtype of K(ATP) channel. The open probability of Kir6.1/SUR2B channels was determined before and after sequential exposure to pinacidil (50 microM) and the combination of pinacidil and phorbol 12,13-dibutyrate (PdBu; 50 nM). Treatment with PdBu caused a decline in channel activity, but this was not seen with an inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate (PdDe; 50 nM). Angiotensin II (0.1 microM) induced a similar inhibition of Kir6.1/SUR2B channels in cells expressing angiotensin AT(1) receptors. The effects of PdBu and angiotensin II were blocked by the PKC inhibitor, chelerythrine (3 microM). Purified PKC inhibited Kir6.1/SUR2B activity (in 0.5 mM ATP/ 0.5 mM ADP), and the inhibition was blocked by a specific peptide inhibitor of PKC, PKC(19-31). In contrast, PdBu increased the activity of recombinant K(ATP) channels composed of Kir6.2 and SUR2B, or the combination of Kir6.1, Kir6.2 and SUR2B subunits. The results indicate that the modulation by PKC of Kir6.1/SUR2B, but not Kir6.2/SUR2B or Kir6.1-Kir6.2/SUR2B channel gating mimics that of native vascular K(NDP) channels. Physiological inhibition of vascular K(ATP) current by vasoconstrictors which utilize intracellular signalling cascades involving PKC is concluded to involve the modulation of K(NDP) channel complexes composed of four Kir6.1 and their associated SUR2B subunits.

Pros and cons of antioxidant use during radiation therapy

Radiation therapy is one of the major treatment modalities in the management of human cancer. While impressive progress like more accurate dosimetry and more precise methods of radiation targeting to tumor tissue has been made, the value of radiation therapy in tumor control may have reached a plateau. At present, two opposing hypotheses regarding the use of antioxidants during radiation therapy have been proposed. One hypothesis states that supplementation with high doses of multiple micronutrients including high dose dietary antioxidants (vitamins C and E, and carotenoids) may improve the efficacy of radiation therapy by increasing tumor response and decreasing some of its toxicity on normal cells. The other hypothesis suggests that antioxidants (dietary or endogenously made) should not be used during radiation therapy, because they would protect cancer cells against radiation damage. Each of these hypotheses is based on different conceptual frameworks that are derived from results obtained from specific experimental designs, and thus, each may be correct within its parameters. The question arises whether any of these concepts and experimental designs can be used during radiation therapy to improve the management of human cancer by this modality. This review has analyzed published data that are used in support of each hypothesis, and has revealed that the current controversies can be resolved, if the results obtained from one experimental design are not extrapolated to the other. This review has also discussed the scientific rationale for a micronutrient protocol that includes high doses of dietary antioxidants (vitamin C, vitamin E succinate and natural beta-carotene) which can be used adjunctively with radiation therapy.

Alpha tocopheryl succinate, retinoic acid and polar carotenoids enhanced the growth-inhibitory effect of a cholesterol-lowering drug on immortalized and transformed nerve cells in culture

OBJECTIVE

Statins (cholesterol lowering drugs) with a closed-ring structure (lovastatin, simvastatin and mevastatin) and an open-ring structure (pravastatin and fluvastatin) are currently used in the management of cardiac disease. Lovastatin and simvastatin inhibit the growth of tumor cells; however, the studies on the effect of a statin in combination with micronutrients such as alpha-tocopheryl succinate (alpha-TS), 13-cis retinoic acid (RA) and polar carotenoids (PC) have never been performed. The primary objective of this study was to investigate the effect of mevastatin alone and in combination with the above micronutrients on the growth of mouse neuroblastoma (NB) cells and rat immortalized dopamine (DA) neurons in culture. In addition, a comparative efficacy of mevastatin and pravastatin on the growth of NB cells was studied.

METHODS

Cells were treated with mevastatin in combination with individual antioxidants, alpha-TS, RA and polar carotenoids, 24 hours after plating. Fresh growth medium and agents were changed at two days after treatment, and the viability in control and experimental groups was determined at three days after treatment by MTT assay. Each experiment was repeated three times with triplicate samples per treatment. Growth in experimental groups was expressed as % of untreated cells.

RESULTS

Mevastatin inhibited the growth of neuroblastoma (NB) cells and immortalized, non-tumorigenic dopamine (DA) neurons in culture in a dose-dependent manner. Immortalized DA neurons were more sensitive to mevastatin than NB cells. Pravastatin at similar concentrations was ineffective in inhibiting the growth of NB cells. Mevastatin in combination with alpha-TS, RA or PC was more effective in reducing the growth of NB and DA neurons than the individual agents.

CONCLUSIONS

Statins with a closed-ring structure can inhibit the growth of established cancer cells as well as immortalized cells (equivalent to pre-malignant lesion), whereas statins with an open-ring structure may be ineffective. A combination of a statin having a closed-ring structure with alpha-TS, RA and PC may be one of the potentially useful anti-cancer agents for prevention and treatment strategies.

Molecular composition of 4-aminopyridine-sensitive voltage-gated K(+) channels of vascular smooth muscle

Voltage-gated K(+) channels (Kv) play a critical role in regulating arterial tone by modulating the membrane potential of vascular smooth muscle cells. Our previous work demonstrated that the dominant 4-aminopyridine (4-AP)-sensitive, delayed rectifier Kv current of rabbit portal vein (RPV) myocytes demonstrates similar 4-AP sensitivity and biophysical properties to Kv1alpha-containing channels. To identify the molecular constituents underlying the 4-AP-sensitive Kv current of vascular myocytes, we characterized the expression pattern of Kv1alpha subunits and their modulatory Kvbeta subunits in RPV. The mRNAs encoding pore-forming subunits Kv1.2, Kv1.4, and Kv1.5 were detected by reverse transcriptase-polymerase chain reaction (RT-PCR), whereas Kv1.1, Kv1.3, and Kv1.6 transcripts were undetectable. Kvbeta1.1, beta1.2, beta1.3, beta2.1, and beta2.2 messages were expressed, whereas Kvbeta3.1 and beta4 mRNAs were undetected by RT-PCR. Kv1.2, Kv1.4, Kv1.5, Kvbeta1.2, beta1.3, and beta2.1 proteins were detected in RPV by Western blotting and/or immunocytochemistry of freshly isolated myocytes. We provide the first evidence, from coimmunoprecipitation studies, for the formation of heteromultimeric Kv channel complexes composed of Kv1.2, Kv1.5, and Kvbeta1.2 subunits in vascular smooth muscle.

Heteromultimeric Kv1.2-Kv1.5 channels underlie 4-aminopyridine-sensitive delayed rectifier K(+) current of rabbit vascular myocytes

The molecular identity of vascular delayed rectifier K(+) channels (K(DR)) is poorly characterized. Inhibition by 4-aminopyridine (4-AP) of K(DR) of rabbit portal vein (RPV) myocytes was studied by patch clamp and compared with that of channels composed of Kv1.5 and/or Kv1.2 subunits cloned from the RPV and expressed in mammalian cells. 4-AP block of K(DR) was pulse-frequency dependent, required channel activation, and was associated with a positive shift in voltage dependence of activation. 4-AP caused a voltage-dependent reduction in mean open time of K(DR). Relief of 4-AP block of whole cell currents during washout required channel activation and was unaffected by voltage. Homotetrameric Kv1.5 channels did not exhibit the shift in voltage dependence of activation exhibited by the native channels. In contrast, Kv1.2 channels displayed a shift in voltage dependence of activation, and this characteristic was also evident during 4-AP treatment when Kv1.2 was coexpressed with Kv1.5 or coupled to Kv1.5 in a tandem construct to produce heterotetrameric [Kv1.5/Kv1.2](2) channels. K(DR) currents were not sensitive to charybdotoxin, which blocks homotetrameric Kv1.2 channels. The findings of this study (1) indicate that vascular K(DR) are inhibited by 4-AP via an open-state block mechanism and trapping of the drug within the pore on channel closure and (2) provide novel evidence based on a comparison of functional characteristics that indicate the dominant form of vascular K(DR) channel complex in RPV involves the heteromultimeric association of Kv1.2 and Kv1.5 subunits.

Differentiation genes: are they primary targets for human carcinogenesis?

In spite of extensive research in molecular carcinogenesis, genes that can be considered primary targets in human carcinogenesis remain to be identified. Mutated oncogenes or cellular growth regulatory genes, when incorporated into normal human epithelial cells, failed to immortalize or transform these cells. Therefore, they may be secondary events in human carcinogenesis. Based on some experimental studies we have proposed that downregulation of a differentiation gene may be the primary event in human carcinogenesis. Such a gene could be referred to as a tumor-initiating gene. Downregulation of a differentiation gene can be accomplished by a mutation in the differentiation gene, by activation of differentiation suppressor genes, and by inactivation of tumor suppressor genes. Downregulation of a differentiation gene can lead to immortalization of normal cells. Mutations in cellular proto-oncogenes, growth regulatory genes, and tumor suppressor genes in immortalized cells can lead to transformation. Such genes could be called tumor-promoting genes. This hypothesis can be documented by experiments published on differentiation of neuroblastoma (NB) cells in culture. The fact that terminal differentiation can be induced in NB cells by adenosine 3',5'-cyclic monophosphate (cAMP) suggests that the differentiation gene in these cells is not mutated, and thus can be activated by an appropriate agent. The fact that cAMP-resistant cells exist in NB cell populations suggests that a differentiation gene is mutated in these cancer cells, or that differentiation regulatory genes have become unresponsive to cAMP. In addition to cAMP, several other differentiating agents have been identified. Our proposed hypothesis of carcinogenesis can also be applied to other human tumors such as melanoma, pheochromocytoma, medulloblastoma, glioma, sarcoma, and colon cancer.

Scientific rationale for using high-dose multiple micronutrients as an adjunct to standard and experimental cancer therapies

We have hypothesized that high-dose multiple micronutrients, including antioxidants, as an adjunct to standard (radiation therapy and chemotherapy) or experimental therapy (hyperthermia and immunotherapy), may improve the efficacy of cancer therapy by increasing tumor response and decreasing toxicity. Several in vitro studies and some in vivo investigations support this hypothesis. A second hypothesis is that antioxidants may interfere with the efficacy of radiation therapy and chemotherapy. This hypothesis is based on the concept that antioxidants will destroy free radicals that are generated during therapy, thereby protecting cancer cells against death. None of the published data on the effect of antioxidants in combination with radiation or chemotherapeutic agents on tumor cells supports the second hypothesis. Scientific rationale in support of a micronutrient protocol to be used as an adjunct to standard or experimental cancer therapy is presented.

State-dependent block of rabbit vascular smooth muscle delayed rectifier and Kv1.5 channels by inhibitors of cytochrome P450-dependent enzymes

The effects of the cytochrome P450 inhibitors clotrimazole, ketoconazole, and 1-aminobenzotriazole (1-ABT) on native delayed rectifier (K(DR)) and cloned Kv1.5 (RPV Kv1.5) K+ channels of rabbit portal vein (RPV) myocytes were determined using whole-cell and single channel patch-clamp analysis. Clotrimazole reduced K(DR) and RPV Kv1.5 whole-cell current with respective Kd values of 1.15 +/- 0.39 and 1.99 +/- 0.6 microM. Clotrimazole acted via an open state blocking mechanism based on the following: 1) the early time course of K(DR) current activation was not affected, but inhibition developed with time during depolarizing steps and increased the rate of decay in current amplitude; 2) the inhibition was voltage-dependent, increasing steeply over the voltage range of K(DR) activation; and 3) mean open time of RPV Kv1.5 channels in inside-out patches was decreased significantly. Ketoconazole reduced K(DR) current amplitude with a Kd value of 38 +/- 3.2 microM. However, ketoconazole acted via a closed (resting) state blocking mechanism: 1) K(DR) amplitude was reduced throughout the duration of depolarizing steps and the rate of decay of current was unaffected, 2) there was no voltage dependence to the block by ketoconazole over the K(DR) activation range, and 3) ketoconazole did not affect mean open time of RPV Kv1.5 channels in inside-out membrane patches. 1-ABT between 0.5 and 3 mM did not affect native K(DR) or RPV Kv1.5 current of rabbit portal vein myocytes. Clotrimazole and ketoconazole, but not 1-ABT, suppress vascular K(DR) channels by direct, state-dependent block mechanisms not involving the modulation of cytochrome P450 enzyme activity.

Peripartum cardiomyopathy: echocardiogram to predict prognosis

Peripartum cardiomyopathy is an uncommon complication of human pregnancy that threatens both the mother and fetus with maternal congestive heart failure. Clinicians must be aware of this problem in order to provide prompt diagnosis and effective treatment that will insure a favorable return of normal left ventricular function.

Comparison of the pharmacological properties of EDHF-mediated vasorelaxation in guinea-pig cerebral and mesenteric resistance vessels

In the presence of L-NNA (100 microM), indomethacin (10 microM) and ODQ (10 microM), acetylcholine induced a concentration-dependent vasorelaxation of guinea-pig mesenteric and middle cerebral arteries precontracted with cirazoline or histamine, but not with high K(+), indicating the contribution of an endothelium-derived hyperpolarizing factor (EDHF). In cerebral arteries, charybdotoxin (ChTX; 0.1 microM) completely inhibited the indomethacin, L-NNA and ODQ-insensitive relaxation; iberiotoxin (IbTX, 0.1 microM), 4-aminopyridine (4-AP, 1 mM), or barium (30 microM) significantly reduced the response; in the mesenteric artery, ChTX and IbTX also reduced this relaxation. Glibenclamide (10 microM) had no affect in either the mesenteric or cerebral artery. Neither clotrimazole (1 microM) nor 7-ethoxyresorufin (3 microM) affected EDHF-mediated relaxation in the mesenteric artery, but abolished or attenuated EDHF-mediated relaxations in the cerebral artery. AM404 (30 microM), a selective anandamide transport inhibitor, did not affect the vasorelaxation response to acetylcholine in the cerebral artery, but in the mesenteric artery potentiated the vasorelaxation response to acetylcholine in an IbTX, and apamin-sensitive, but SR 141816A-insensitive manner. Ouabain (100 microM) almost abolished EDHF-mediated relaxation in the mesenteric artery, but enhanced the relaxation in the cerebral artery whereas the addition of K(+) (5 - 20 mM) to precontracted guinea-pig cerebral or mesenteric artery induced further vasoconstriction. These data suggest that in the guinea-pig mesenteric and cerebral arteries different EDHFs mediate acetylcholine-induced relaxation, however, EDHF is unlikely to be mediated by K(+).

Inhibition by protein kinase C of the K(NDP) subtype of vascular smooth muscle ATP-sensitive potassium channel

ATP-sensitive K(+) channels (K(ATP)) contribute to the regulation of tone in vascular smooth muscle cells. We determined the effects of protein kinase C (PKC) activation on the nucleoside diphosphate-activated (K(NDP)) subtype of vascular smooth muscle K(ATP) channel. Phorbol 12,13-dibutyrate (PdBu) and angiotensin II inhibited K(NDP) activity of C-A patches of rabbit portal vein (PV) myocytes, but an inactive phorbol ester was without effect, and pretreatment with PKC inhibitor prevented the actions of PdBu. Constitutively active PKC inhibited K(NDP) in I-O patches but was without effect in the presence of a specific peptide inhibitor of PKC. PdBu increased the duration of a long-lived interburst closed state but was without effect on burst duration or intraburst kinetics. PdBu treatment inhibited K(NDP), but not a 70-pS K(ATP) channel of rat PV. The results indicate that the K(NDP) subtype of vascular smooth muscle K(ATP) channel is inhibited by activation of PKC. Control of K(NDP) activity by intracellular signaling cascades involving PKC may, therefore, contribute to control of tone and arterial diameter by vasoconstrictors.

Vitamin E (d-alpha-tocopheryl succinate) decreases mitotic accumulation in gamma-irradiated human tumor, but not in normal, cells

Previous studies have shown that treatment of tumor cells in vitro with d-alpha-tocopheryl succinate (alpha-TS), a most effective form of vitamin E, alone or in combination with X-irradiation, reduced the growth of these cells more than that produced by individual agents. However, it is unknown whether alpha-TS, alone or in combination with gamma-irradiation, would produce similar effects on normal cells. To study this, we have compared the effects of alpha-TS on three human tumor cell lines, HeLa (cervical carcinoma), OVGI (ovarian carcinoma), and A549 (lung carcinoma), with the effects on three human normal fibroblast lines, GM2149, AG1522, and HF19. Results showed that alpha-TS treatment of HeLa cells for 20 hours caused inhibition of growth in a dose-dependent manner, but normal human fibroblasts treated similarly with alpha-TS did not show such an effect. alpha-TS treatment for 20 hours also decreased mitotic accumulation in all three tumor cell lines but did not produce such an effect in any of the normal fibroblasts. As expected, gamma-irradiation with 1 Gy decreased mitotic accumulation in human tumor cells and normal fibroblasts; however, alpha-TS treatment for 24 hours before, during, and after irradiation for the entire experimental period further decreased mitotic accumulation in human tumor cells but not in normal cells. These data suggest that effects of alpha-TS, alone or in combination with gamma-irradiation, are selective for tumor cells. Therefore, existing fear that antioxidants such as vitamin E may protect cancer cells from free radical damage during radiation therapy is not justified.

Cicatricial pemphigoid with an upper airway lesion

Cicatricial pemphigoid is an unusual mucocutaneous disease that is characterized by subepidermal blister formation involving the oral and conjunctival membranes. The oral lesions are expressed as erythema and induration and have rarely been associated with upper airway obstruction. We report the case of a patient with dyspnea and an abnormal flow-volume loop who was found to have subglottic compromise due to cicatricial pemphigoid. Immunosuppressive therapy improved his symptoms and air flow.

Relative sensitivity of undifferentiated and cyclic adenosine 3',5'-monophosphate-induced differentiated neuroblastoma cells to cyclosporin A: potential role of beta-amyloid and ubiquitin in neurotoxicity

Cyclosporin A is routinely used in transplant therapy following allogeneic or xenogeneic tissue transplantation to prevent rejection. This immunosuppressive drug is also neurotoxic; however, its mechanisms of action for neurotoxicity are poorly understood. Undifferentiated and cyclic adenosine 3',5'-monophosphate (cAMP)-induced differentiated neuroblastoma (NB) cells were used as an experimental model to study the toxicity of cyclosporin A. Results showed that cyclosporin A promoted the outgrowth of neurites and inhibited the growth of undifferentiated NB cells. When cyclosporin A was added simultaneously with RO20-1724, an inhibitor of cyclic nucleotide phosphodiesterase, or with prostaglandin E1, a stimulator of adenylate cyclase, it markedly enhanced the growth inhibitory and differentiation effects of these cAMP-stimulating agents. In addition, cyclosporin A added to cAMP-induced differentiated NB cells caused dose-dependent degeneration of these cells as evidenced by the vacuolization of cytoplasm and the fragmentation of nuclear and cytoplasmic materials; however, neurites remained intact. Cyclosporin A alone did not alter the intensity of cell immunostaining for ubiquitin or beta-amyloid peptide (amino acids 1-14) (Abeta1-14); however, it enhanced the intensity of staining for both ubiquitin and Abeta in cells that were treated with cAMP-stimulating agents. The intensity of staining of amyloid precursor protein (amino acids 44-63) (APP44-66) did not change in any treated group, suggesting that the increase in Abeta staining is due to increased processing of APP to Abeta. We propose that one of the mechanisms of cyclosporin A-induced neurotoxicity involves increased levels of Abeta and ubiquitin.

Multiple antioxidants in the prevention and treatment of Alzheimer disease: analysis of biologic rationale

The etiology of Alzheimer disease (AD) is not well understood; therefore, neither prevention strategies nor long-term effective treatment modalities are available for this disease. Based on laboratory and clinical studies, it appears that reactive oxygen species (ROS) and reactive nitrogen species (RNS) that are generated extracellularly and intracellularly by various mechanisms are among the major intermediary risk factors that initiate and promote neurodegeneration in idiopathic AD. Therefore, multiple antioxidant supplements could be useful in the prevention of AD, and as an adjunct to standard therapy in the treatment of AD. The products of inflammatory reactions such as prostaglandins (PGs; PGE1 and PGA1), free radicals, cytokines, and complement proteins are neurotoxic. Nonsteroidal antiinflammatory drugs (NSAIDs), which inhibit the synthesis of PGs, reduce the rate of deterioration of cognitive functions in patients with advanced AD. Cholinergic drugs are routinely used in the treatment of AD to improve cognitive functions. Therefore, we propose that a combination of multiple antioxidants and NSAIDs may be more beneficial in the prevention of AD, and that this combination taken together with cholinergic drugs may be more effective in the treatment of AD than the individual agents alone. We also hypothesize that, in idiopathic AD, epigenetic components of neurons such as mitochondria, membranes, other membranous structures, and protein modifications--rather than the genes of neurons--are the primary targets for the action of neurotoxins including free radicals. In some familial AD, mutations in amyloid precursor protein and presenilins are associated with the risk of early onset of this disease; however, their mechanisms of action are not fully understood.

Multiple antioxidants in the prevention and treatment of neurodegenerative disease: analysis of biologic rationale

Parkinson's disease and Alzheimer's disease are major progressive neurologic disorders, the risk of which increases with advancing age (65 years and over). In familial cases, however, early onset of disease (35-65 years) is observed. In spite of extensive basic and chemical research on Parkinson's disease and Alzheimer's disease, no preventive or long-term effective treatment strategies are available. The analysis of existing literature suggests that oxidative stress is a major intermediary risk factor for the action of diverse groups of neurotoxins that are involved in these neurodegenerative diseases. In this review, it is proposed that the epigenetic components (mitochondria, other organelles, membranes, protein modification) rather than nuclear genes of neurons are the primary targets for the action of neurotoxins, including free radicals. In addition, a scientific rationale for using multiple antioxidants in clinical trials for the prevention of Parkinson's disease and Alzheimer's disease among high-risk populations, and as an adjunct to standard therapy in the treatment of these diseases is presented.

Adenosine 3',5'-cyclic monophosphate increases processing of amyloid precursor protein (APP) to beta-amyloid in neuroblastoma cells without changing APP levels or expression of APP mRNA

Beta-Amyloid (Abeta), a 39-43 residue peptide generated by splicing of the amyloid precursor protein (APP), is one of the major components of senile plaques which are the hallmark of Alzheimer's disease (AD); and therefore, a role of Abeta in neuronal degeneration has been proposed. The factors which regulate the levels of Abeta have not been fully identified. Since an elevation of the intracellular levels of adenosine, 3', 5'-cyclic monophosphate (cAMP) in neuroblastoma cells (NB) induces terminal differentiation, and since these differentiated NB cells undergo spontaneous degeneration, the role of cAMP in the regulation of Abeta levels in these cells have been investigated. In order to determine the specificity of the effect of cAMP on nerve cells, rat glioma cells (C-6) were investigated in a similar manner. Results showed that an elevation of the levels of cAMP in NB cells enhances the intensity of Abeta immunostaining without changing the levels of APP or APP mRNA. This suggests that the rate of processing of APP to Abeta increases following an elevation of cAMP level in NB cells. Data also revealed that an elevation of cAMP level in glioma cells did not alter the intensity of staining with APP or Abeta.

Multiple antioxidants in the prevention and treatment of Parkinson's disease

Parkinson's disease (PD) is one of the major progressive neurological disorders for which no preventative or long-term effective treatment strategies are available. Epidemiologic studies have failed to identify specific environmental, dietary or lifestyle risk factors for PD except for toxic exposure to manganese, meperidine (Demerol, the "designer drug" version of which often contains a toxic byproduct of the synthesis, 1-methyl-4-phenyl 1,2,3,6 tetrahydropyridine [MPTP]), and some herbicides and pesticides. The search for genetic risk factors such as mutation, overexpression or underexpression of nuclear genes in DA neurons in idiopathic PD has not been successful as yet. Polymorphism in certain genes appears to be a risk factor, but there is no direct evidence for the causal relationship between polymorphism and increased risk of PD. In familial PD, mutation in the alpha-synuclein gene is associated with the disease, but a direct role of this gene in degeneration of DA neurons remains to be established. Although mutations in the Parkin gene has been associated with autosomal recessive juvenile Parkinson's disease, the role of this gene mutation in causing degeneration of DA neurons has not been defined. We have reported that in hereditary PD, a mutation in the alpha-synuclein gene may increase the sensitivity of DA neurons to neurotoxins. We hypothesize that, in idiopathic PD, epigenetic (mitochondria, membranes, protein modifications) rather than genetic events are primary targets which, when impaired, initiate degeneration in DA neurons, eventually leading to cell death. Although the nature of neurotoxins that cause degeneration in DA neurons in PD is not well understood, oxidative stress is one of the intermediary risk factors that could initiate and/or promote degeneration of DA neurons. Therefore, supplementation with antioxidants may prevent or reduce the rate of progression of this disease. Supplementation with multiple antioxidants at appropriate doses is essential because various types of free radicals are produced, antioxidants vary in their ability to quench different free radicals and cellular environments vary with respect to their lipid and aqueous phases. L-dihydroxyphenylalanine (L-dopa) is one of the agents used in the treatment of PD. Since L-dopa is known to produce free radicals during its normal metabolism, the combination of L-dopa with high levels of multiple antioxidants may improve the efficacy of L-dopa therapy.

Cyclosporin A regulates the levels of cyclophilin A in neuroblastoma cells in culture

Cyclophilin A (CyP-A), a member of a highly conserved family of proteins, immunophilins, is the major intracellular receptor for the immunosuppressive drug, cyclosporin A (CsA). CyP-A is widely expressed in many tissues, but is found in the highest concentration in brain tissues and may perform critical neuronal functions. CsA is a known neurotoxin. Therefore, understanding the regulation of CyP-A levels in nerve cells, particularly by CsA, is important. We have utilized murine neuroblastoma (NB) cells as an experimental model to investigate this issue. Our results show that CsA alone was sufficient to induce morphological differentiation in undifferentiated NB cells and to increase CyP-A levels as determined by immunostaining. However, inducing terminal differentiation by elevating adenosine 3',5'-cyclic monophosphate (cAMP) levels using either 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (RO20-1724), an inhibitor of cyclic nucleotide phosphodiesterase, or prostaglandin E1 (PGE1), a stimulator of adenylate cyclase, was not sufficient to increase CyP-A levels. CsA was required to increase CyP-A levels in both RO20-1724- and PGE1-induced differentiated NB cells. Increases in CyP-A levels, however, occurred without any change in the expression of the CyP-A gene as determined by reverse-transcriptase polymerase-chain reaction analysis using (CyP-A)-specific primers. These results suggest that CsA regulates the level of its own binding protein, CyP-A, in both undifferentiated and cAMP-induced differentiated NB cells in culture.

Identification, cloning and expression of rabbit vascular smooth muscle Kv1.5 and comparison with native delayed rectifier K+ current

1. The molecular basis of voltage-gated, delayed rectifier K+ (KDR) channels in vascular smooth muscle cells is poorly defined. In this study we employed (i) an antibody against Kv1.5 and (ii) a cDNA clone encoding Kv1.5 derived from rabbit portal vein (RPV) to demonstrate Kv1.5 expression in RPV and to compare the properties of RPVKv1.5 expressed in mammalian cells with those of native RPV KDR current. 2. Expression of Kv1.5 channel protein in RPV was demonstrated by (i) immunocytolocalization of an antibody raised against a C-terminal epitope of mouse cardiac Kv1.5 in permeabilized, freshly isolated RPV smooth muscle cells and (ii) isolation of a cDNA clone encoding RPVKv1.5 by reverse transcription-polymerase chain reaction (RT-PCR) using mRNA derived from endothelium-denuded and adventitia-free RPV. 3. RPVKv1.5 cDNA was expressed in mammalian L cells and human embryonic kidney (HEK293) cells and the properties of the expressed channels compared with those of native KDR channels of freshly dispersed myocytes under identical conditions. 4. The kinetics and voltage dependence of activation of L cell-expressed RPVKv1.5 and native KDR current were identical, as were the kinetics of recovery from inactivation and single channel conductance. In contrast, there was little similarity between HEK293 cell-expressed RPVKv1.5 and native KDR current. 5. Inactivation occurred with the same voltage for half-maximal availability, but the kinetics and slope constant for the voltage dependence of inactivation for L cell-expressed RPVKv1.5 and the native current were different: slow time constants were 6.5 +/- 0.6 and 3.5 +/- 0.4 s and slope factors were 4.7 +/- 0.2 and 7.0 +/- 0.8 mV, respectively. 6. This study provides immunofluorescence and functional evidence that Kv1.5 alpha-subunits are a component of native KDR channels of vascular smooth muscle cells of RPV. However, the differences in kinetics and voltage sensitivity of inactivation between L cell- and HEK293 cell-expressed channels and native KDR channels provide functional evidence that vascular KDR current is not due to homomultimers of RPV Kv1.5 alone. The channel structure may be more complex, involving heteromultimers and modulatory Kvbeta-subunits, and/or native KDR current may have other components involving Kvalpha-subunits of other families.

High doses of multiple antioxidant vitamins: essential ingredients in improving the efficacy of standard cancer therapy

Numerous articles and several reviews have been published on the role of antioxidants, and diet and lifestyle modifications in cancer prevention. However, the potential role of these factors in the management of human cancer have been largely ignored. Extensive in vitro studies and limited in vivo studies have revealed that individual antioxidants such as vitamin A (retinoids), vitamin E (primarily alpha-tocopheryl succinate), vitamin C (primarily sodium ascorbate) and carotenoids (primarily polar carotenoids) induce cell differentiation and growth inhibition to various degrees in rodent and human cancer cells by complex mechanisms. The proposed mechanisms for these effects include inhibition of protein kinase C activity, prostaglandin E1-stimulated adenylate cyclase activity, expression of c-myc, H-ras, and a transcription factor (E2F), and induction of transforming growth factor-beta and p21 genes. Furthermore, antioxidant vitamins individually or in combination enhance the growth-inhibitory effects of x-irradiation, chemotherapeutic agents, hyperthermia, and biological response modifiers on tumor cells, primarily in vitro. These vitamins, individually, also reduce the toxicity of several standard tumor therapeutic agents on normal cells. Low fat and high fiber diets can further enhance the efficacy of standard cancer therapeutic agents; the proposed mechanisms for these effects include the production of increased levels of butyric acid and binding of potential mutagens in the gastrointestinal tract by high fiber and reduced levels of growth promoting agents such as prostaglandins, certain fatty acids and estrogen by low fat. We propose, therefore, a working hypothesis that multiple antioxidant vitamin supplements together with diet and lifestyle modifications may improve the efficacy of standard and experimental cancer therapies.

Endothelium-derived hyperpolarizing factor(s): species and tissue heterogeneity

1. Endothelium-derived relaxing factor is almost universally considered to be synonymous with nitric oxide (NO); however, it is now well established that at least two other chemically distinct species (prostacyclin (PGI2) and a hyperpolarizing factor) may also contribute to endothelium-dependent relaxation. 2. Only relatively few studies have provided definitive evidence that an endothelium-derived hyperpolarizing factor (EDHF), which is neither NO nor PGI2, exists as a chemical mediator. 3. There is a lack of agreement as to the likely chemical identity of this putative factor. Some evidence suggests that EDHF may be a cytochrome P450-derived arachidonic acid product, possibly an epoxyeicosatrienoic acid (EET); conflicting evidence supports an endogenous cannabinoid as the mediator and still other studies infer an unknown mediator that is neither a cytochrome P450 nor a cannabinoid. 4. Data from our laboratory with a rabbit carotid artery 'sandwich' preparation have provided evidence that a mediator that meets the pharmacological expectations of a cytochrome P450 product is an EDHF. 5. Data from guinea-pig mesenteric arterioles suggest that EDHF is not a cytochrome P450 product, whereas in guinea-pig middle cerebral arteries, relaxation mediated by the NO/PGI2-independent mediator(s) is sensitive to cytochrome P450 inhibitors. In addition, in the rabbit middle cerebral artery, it is likely that endothelium-dependent hyperpolarization is mediated by both NO and PGI2. 6. In conclusion, these data indicate that EDHF is unlikely to be a single factor and that considerable tissue and species differences exist for the nature and cellular targets of the hyperpolarizing factors.

Activation of vascular smooth muscle K+ channels by endothelium-derived relaxing factors

1. Endothelium-derived relaxing factors (EDRF), including nitric oxide (NO), prostacyclin (PGI2) and an as yet uncharacterized endothelium-derived hyperpolarizing factor (EDHF), are now recognized to induce relaxation of vascular smooth muscle, in part via the activation of K+ channels. 2. Experiments using selective K+ channel blockers, including iberiotoxin (IbTX), glibenclamide, apamin and 4-aminopyridine (4-AP) to inhibit endothelium-induced relaxation suggest that more than one type of K+ channel may be involved, depending on the species and tissue, including: (i) large conductance Ca(2+)-activated (BKCa) channels; (ii) ATP-sensitive (KATP) channels; (iii) small conductance Ca(2+)-activated (SKCa) channels; and (iv) voltage-gated (Kv) K+ channels. 3. Recent observations suggest a role for Kv channels in some vessels based on a sensitivity of NO- and PGI2-mediated relaxations to 4-AP, as well as a complete suppression of EDHF-dependent relaxation by a combination of charybdotoxin (ChTX) and apamin but not IbTX and apamin. 4. The molecular identity of the K+ channels affected by EDRF is not well characterized. Recently, findings indicate that the pore-forming alpha-subunit tetramers of vascular smooth muscle BKCa channels are due to the expression of the so-called Slo channel gene. The identities of the KATP, SKCa and Kv channels involved in endothelium-dependent vasodilation are not known. 5. The component of whole-cell Kv current affected by PGI2 may be due to slowly inactivating, 4-AP-sensitive, 15 pS delayed-rectifier K+ channels (KDR); the activity of these channels in vascular myocytes is increased by forskolin and protein kinase A (PKA) and rabbit portal vein Kv1.5 pore-forming alpha-subunits, which appear to be a component of native KDR current and possess consensus phosphorylation sequences for PKA.

Delayed rectifier K+ current of dog bronchial myocytes: effect of pollen sensitization and PKC activation

The properties of delayed rectifier K+ current [IK(dr)] of canine airway smooth muscle cells isolated from small bronchi and its modulation by protein kinase C (PKC) were studied by whole cell patch clamp. IK(dr) activated positive to -40 mV, with half-maximal activation at -16 +/- 1.2 mV (n = 15) and average current density of 31 +/- 2.6 pA/pF (n = 15) at +30 mV. The capacitive surface area, current density, and voltage dependence of activation of IK(dr) of myocytes of ragweed pollen-sensitized dogs were not different from age-matched control dogs. However, the sensitization reduced the availability of IK(dr) between -40 and -20 mV due to a hyperpolarizing shift in the voltage dependence of steady-state inactivation (-29.9 +/- 1.2 in sensitized versus -26.0 +/- 0.7 mV in control dogs, n = 9 and 11, respectively; P < 0.05). PKC activation with diacylglycerol analog or phorbol ester depressed IK(dr) amplitude, whereas an inactive diacylglycerol analog had no effect. The hyperpolarizing shift in voltage dependence of inactivation and/or modulation of IK(dr) by PKC may be two mechanisms that contribute to the enhanced reactivity of bronchial tissues from ragweed pollen-sensitized dogs.

Beta-adrenoceptor activation and PKA regulate delayed rectifier K+ channels of vascular smooth muscle cells

Macroscopic 4-aminopyridine (4-AP)-sensitive, delayed rectifier K+ current of vascular smooth muscle cells is increased during beta-adrenoceptor activation with isoproterenol via a signal transduction pathway involving adenylyl cyclase and cAMP-dependent protein kinase (PKA) (Aiello, E. A., M. P. Walsh, and W. C. Cole. Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H926-H934, 1995.). In this study, we identified the single delayed rectifier K+ (KDR) channel(s) of rabbit portal vein myocytes affected by treatment with isoproterenol or the catalytic subunit of PKA. 4-AP-sensitive KDR channels of 15.3 +/- 0.6 pS (n = 5) and 14.8 +/- 0.6 pS (n = 5) conductance, respectively, were observed in inside-out (I-O) and cell-attached (C-A) membrane patches in symmetrical KCl recording conditions. The kinetics of activation (time constant of 10.7 +/- 3. 02 ms) and inactivation (fast and slow time constants of 0.3 and 2.5 s, respectively) of ensemble currents produced by these channels mimicked those reported for inactivating, 4-AP-sensitive whole cell KDR current of vascular myocytes. Under control conditions, the open probability (NPo) of KDR channels of C-A membrane patches at -40 mV was 0.014 +/- 0.005 (n = 8). Treatment with 1 microM isoproterenol caused a significant, approximately threefold increase in NPo to 0. 041 +/- 0.02 (P < 0.05). KDR channels of I-O patches exhibited rundown after approximately 5 min, which was not affected by ATP (5 mM) in the bath solution. Treatment with the purified catalytic subunit of PKA (50 nM; 5 mM ATP) restored KDR channel activity and caused NPo to increase from 0.011 +/- 0.003 to 0.138 +/- 0.03 (P < 0. 05; n = 11). These data indicate that small-conductance, 15-pS KDR channels are responsible for inactivating the macroscopic delayed rectifier K+ current of rabbit portal vein myocytes and that the activity of these channels is enhanced by a signal transduction mechanism involving beta-adrenoceptors and phosphorylation by PKA at a membrane potential consistent with that observed in the myocytes in situ.

Roles of calcium-activated and voltage-gated delayed rectifier potassium channels in endothelium-dependent vasorelaxation of the rabbit middle cerebral artery

1. The cellular mechanism(s) of action of endothelium-derived vasodilator substances in the rabbit middle cerebral artery (RMCA) were investigated. Specifically, the subtypes of potassium channels involved in the effects of endothelium-derived relaxing factors (EDRFs) in acetylcholine (ACh)-induced endothelium-dependent vasorelaxation in this vessel were systematically compared. 2. In the endothelium-intact RMCA precontracted with histamine (3 microM), ACh induced a concentration-dependent vasorelaxation, which was sensitive to indomethacin (10 microM) or N(G)-nitro-L-arginine (L-NOARG; 100 microM); pD2 values 8.36 vs 7.40 and 6.38, P < 0.01 for both, n = 6 and abolished by a combination of both agents. ACh caused relaxation in the presence of high K+ PSS (40 mM KCl), which was not affected by indomethacin, but abolished by L-NOARG and a combination of indomethacin and L-NOARG. 3. In the presence of indomethacin, relaxation to ACh in the endothelium-intact RMCA precontracted with histamine was unaffected by either glibenclamide (10 microM), an ATP-sensitive K+ channel (K[ATP]) blocker, 4-aminopyridine (4-AP, 1 mM) or dendrotoxin (DTX, 0.1 microM), delayed rectifier K channel (Kv) blockers. However, relaxation responses to ACh were significantly inhibited by either LY83583 (10 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM), guanylyl cyclase inhibitors, or charybdotoxin (CTX; 0.1 microM), iberiotoxin (ITX, 0.1 microM) and apamin (APA, 0.1 microM), large conductance Ca2+-activated K+ channels (BK[Ca]) blocker and small conductance Ca2+-activated K+ channel (SK[Ca]) blocker, respectively. 4. In the presence of L-NOARG, relaxation to ACh was unaffected by glibenclamide or the cytochrome P450 mono-oxygenase inhibitor, clotrimazole (1 microM), but was significantly inhibited by either 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536, 10 microM) and 2',3'-dideoxyadenosine (2',3'-DDA, 30 microM), adenylyl cyclase inhibitors, or 4-AP, DTX, CTX, ITX and APA. 5. In the endothelium-denuded RMCA precontracted with histamine, authentic NO-induced relaxation was unaffected by glibenclamide, 4-AP and DTX, but significantly reduced by ODQ, ITX and APA. Authentic prostaglandin I2 (PGI2)-induced relaxation was unaffected by glibenclamide, but significantly reduced by 2',3'-DDA, 4-AP, DTX, ITX and APA. Forskolin-induced relaxation was significantly inhibited by high K+, CTX and 4-AP. 6. These results indicate that: (1) in the RMCA the EDRFs released by ACh are NO and a prostanoid (presumably PGI2), and there is no evidence for the release of a non-NO/PGI2 endothelium-derived hyperpolarizing factor (EDHF), (2) K(Ca) channels are involved in NO-mediated relaxation of the RMCA but both K(Ca) and Kv channels are involved in PGI2-mediated relaxation.

Contrasting effects of vitamins as modulators of apoptosis in cancer cells and normal cells: a review

Individual vitamins can induce direct apoptosis or indirect apoptosis via cell differentiation in cancer cells; however, they can also stimulate antiapoptotic events in certain cancer cells. These effects depend on the dose, type, and form of vitamins and the type of tumor cells. A mixture of antioxidant vitamins is more effective than individual vitamins, and there is no evidence that such a mixture ever stimulates antiapoptotic events in cancer cells. Vitamins in combination with nonvitamin, direct-acting, apoptotic agents (X-rays, chemotherapeutic agents, and hyperthermia) or in combination with nonvitamin, indirect-acting, apoptotic agents (adenosine 3',5'-cyclic monophosphate, butyric acid, and interferon) produce a greater extent of apoptotic death in cancer cells in culture. Certain antioxidant vitamins may reduce the efficacy of some chemotherapeutic agents on rodent fibrosarcoma cells. In contrast to vitamin-induced apoptosis in cancer cells, normal cells never undergo apoptotic death after treatment with vitamins (not including retinoids). On the contrary, vitamins protect normal cells against apoptosis induced by a certain group of chemicals. The reasons for this differential effect of vitamins on cancer and normal cells are unknown. The genetic regulation of apoptosis in cancer cells has not been adequately defined. Such studies would help in identifying molecular targets that can be used to develop effective doses of vitamins or new drugs to induce apoptosis selectively in cancer cells.

Ca2+ permeation through Na+ channels in guinea pig ventricular myocytes

This study was undertaken to test the hypothesis that, in the absence of extracellular Na+, Ca2+ can permeate tetrodotoxin (TTX)-sensitive Na+ channels in Cs(+)-loaded whole cell voltage-clamped guinea pig ventricular myocytes (22-24 degrees C). With 10 mM extracellular Ca2+, 50-ms step depolarizations (-50 to +25 mV) from holding potentials of -100 or -80 mV elicited fast and slow types of inward current: 1) a small (< 400 pA) dihydropyridine-insensitive inward current that exhibited similar voltage dependence to that of Na+ channels, with an activation threshold and peak near -45 mV and -30 mV, respectively; and 2) a larger and slower L-type Ca2+ current that activated and peaked at more positive potentials. Extracellular replacement of Ca2+ by Mg2+ abolished both currents. The lack of sensitivity of the low-threshold Ca(2+)-current amplitude to 50 or 200 microM Ni2+ suggests that this current is not produced by T-type Ca2+ current. In contrast, TTX dose dependently inhibited the low-threshold Ca2+ current, with a half-maximal inhibition concentration of 2.4 microM. Veratridine (10-50 microM), a plant alkaloid that alters the gating and permeability properties of Na+ current, induced an outward shift of time-dependent current during steps to -25 mV and typical slowly decaying inward tail currents after repolarization to -80 mV. Cell exposure to 10 and 50 microM extracellular Na+ inhibited the inward current by 21.2 +/- 3.9% (n = 23) and 14.0 +/- 3.0% (n = 14), respectively, whereas 1 microM Na+ (n = 14) was without effect. The application of 200 microM Na+ produced a small enhancement of the current (+6.2 +/- 4.1%; n = 14) which was just at the limit of significance. Our data support the notion that Ca2+ can permeate cardiac Na+ channels in the absence of an agonist and external Na+.

NO/PGI2-independent vasorelaxation and the cytochrome P450 pathway in rabbit carotid artery

1. The nature and cellular mechanisms that are responsible for endothelium-dependent relaxations resistant to indomethacin and NG-nitro-L-arginine methyl ester (L-NAME) were investigated in phenylephrine (PE) precontracted isolated carotid arteries from the rabbit. 2. In the presence of the cyclo-oxygenase inhibitor, indomethacin (10 microM), acetylcholine (ACh) induced a concentration- and endothelium-dependent relaxation of PE-induced tone which was more potent than the calcium ionophore A23187 with pD2 values of 7.03 +/- 0.12 (n = 8) and 6.37 +/- 0.12 (n = 6), respectively. The ACh-induced response was abolished by removal of the endothelium, but was not altered when indomethacin was omitted (pD2 value 7.00 +/- 0.10 and maximal relaxation 99 +/- 3%, n = 6). Bradykinin and histamine (0.01-100 microM) had no effect either upon resting or PE-induced tone (n = 5). 3. In the presence of indomethacin plus the NO synthase inhibitor, L-NAME (30 microM), the response to A23187 was abolished. However, the response to ACh was not abolished, although it was significantly inhibited with the pD2 value and the maximal relaxation decreasing to 6.48 +/- 0.10 and 67 +/- 3%, respectively (for both P < 0.01, n = 8). The L-NAME/indomethacin insensitive vasorelaxation to ACh was completely abolished by preconstriction of the tissues with potassium chloride (40 mM, n = 8). 4. The Ca(2+)-activated K+ (KCa) channel blockers, tetrabutylammonium (TBA, 1 mM, n = 5) and charybdotoxin (CTX, 0.1 microM, n = 5), completely inhibited the nitric oxide (NO) and prostacyclin (PGI2)-independent relaxation response to ACh. However, iberiotoxin (ITX, 0.1 microM, n = 8) or apamin (1-3 microM, n = 6) only partially inhibited the relaxation. 5. Inhibitors of the cytochrome P450 mono-oxygenase, SKF-525A (1-10 microM, n = 6), clotrimazole (1 microM, n = 5) and 17-octadecynoic acid (17-ODYA, 3 microM, n = 7) also reduced the NO/PGI2-independent relaxation response to ACh. 6. In endothelium-denuded rings of rabbit carotid arteries, the relaxation response to exogenous NO was not altered by either KCa channel blockade with apamin (1 microM, n = 5) or CTX (0.1 microM, n = 5), or by the cytochrome P450 mono-oxygenase blockers SKF-525A (10 microM, n = 4) and clotrimazole (10 microM, n = 5). However, the NO-induced response was shifted to the right by LY83583 (10 microM, n = 4), a guanylyl cyclase inhibitor, with the pD2 value decreasing from 6.95 +/- 0.14 to 6.04 +/- 0.09 (P < 0.01). 7. ACh (0.01-100 microM) induced a concentration-dependent relaxation of PE-induced tone in endothelium-denuded arterial segments sandwiched with endothelium-intact donor segments. This relaxation to ACh was largely unaffected by indomathacin (10 microM) plus L-NAME (30 microM), but abolished by the combination of indomethacin, L-NAME and TBA (1 mM, n = 5). 8. These data suggest that in the rabbit carotid artery: (a) ACh can induce the release of both NO and EDHF, whereas A23187 only evokes the release of NO from the endothelium, (b) the diffusible EDHF released by ACh may be a cytochrome P450-derived arachidonic acid metabolite, and (c) EDHF-induced relaxation involves the opening of at least two types of KCa channels, whereas NO mediates vasorelaxation via a guanosine 3': 5'-cyclic monophosphate (cyclic GMP)-mediated pathway, in which a cytochrome P450 pathway and KCa channels do not seem to be involved.