Hypoxic preconditioning and cell death from oxygen/glucose deprivation co-opt a subset of the unfolded protein response in hippocampal neurons.

The state of protein folding in the endoplasmic reticulum (ER), via the unfolded protein response (UPR), regulates a pro- or anti-apoptotic cell fate. Hypoxic preconditioning (HPC) is a potent anti-apoptotic stimulus, wherein ischemic neural injury is averted by a non-damaging exposure to hypoxia. We tested if UPR modulation contributes to the pro-survival/anti-apoptotic phenotype in neurons preconditioned with hypoxia, using organotypic cultures of rat hippocampus as a model system. Pharmacologic induction of the UPR with tunicamycin increased mRNA of 79 of 84 UPR genes and replicated the pro-survival phenotype of HPC, whereas only small numbers of the same mRNAs were upregulated at 0, 6 and 24h after HPC. During the first 24h after HPC, protein signals in all 3 UPR pathways increased at various times: increased ATF4, phosphorylation of eif2α and IRE1, cleavage of xbb1 mRNA and cleavage of ATF6. Pharmacologic inhibition of ATF6 and IRE1 blocked HPC. Ischemia-like conditions (oxygen/glucose deprivation, OGD) caused extensive neuron cell damage and involved some of the same UPR protein signals as HPC. In distinction to HPC and tunicamycin, OGD caused widespread suppression of UPR genes: 55 of 84 UPR gene mRNAs were numerically downregulated. We conclude that although HPC and ischemic cell death in hippocampal neurons involve protein-based signaling in all 3 UPR pathways, these processes co-opt only a subset of the genomic response elicited by agents known to cause protein misfolding, possibly because of persistent transcription/translation arrest induced by hypoxia and especially OGD.

Focal amplification of the androgen receptor gene in hormone-naive human prostate cancer.

BACKGROUND: Androgen receptor (AR)-gene amplification, found in 20-30% of castration-resistant prostate cancer (CRPCa) is proposed to develop as a consequence of hormone-deprivation therapy and be a prime cause of treatment failure. Here we investigate AR-gene amplification in cancers before hormone deprivation therapy. METHODS: A tissue microarray (TMA) series of 596 hormone-naive prostate cancers (HNPCas) was screened for chromosome X and AR-gene locus-specific copy number alterations using four-colour fluorescence in situ hybridisation. RESULTS: Both high level gain in chromosome X (≥4 fold; n=4, 0.7%) and locus-specific amplification of the AR-gene (n=6, 1%) were detected at low frequencies in HNPCa TMAs. Fluorescence in situ hybridisation mapping whole sections taken from the original HNPCa specimen blocks demonstrated that AR-gene amplifications exist in small foci of cells (≤ 600 nm, ≤1% of tumour volume). Patients with AR gene-locus-specific copy number gains had poorer prostate cancer-specific survival. CONCLUSION: Small clonal foci of cancer containing high level gain of the androgen receptor (AR)-gene develop before hormone deprivation therapy. Their small size makes detection by TMA inefficient and suggests a higher prevalence than that reported herein. It is hypothesised that a large proportion of AR-amplified CRPCa could pre-date hormone deprivation therapy and that these patients would potentially benefit from early total androgen ablation.

Hypothermia and rewarming injury in hippocampal neurons involve intracellular Ca2+ and glutamate excitotoxicity.

This study examines the causes of hypothermia and rewarming injury in CA1, CA3, and dentate neurons in rat hippocampal slice cultures. Neuronal death, assessed with propidium iodide or Sytox fluorescence, Fluoro-Jade labeling, and Cresyl Violet staining, depended on the severity and duration of hypothermia. More than 6 h at temperatures less than 12 °C followed by rewarming to 37 °C (profound hypothermia and rewarming, PH/RW) caused swelling and death in large number of neurons in CA1, CA3, and dentate. During PH, [ATP] decreased and [Ca(2+)](I) and extracellular [glutamate] increased, with neuron rupture and nuclear condensation following RW. The data support the hypothesis that neuronal death from PH/RW is excitotoxic, due to ATP loss, glutamate receptor activation and Ca(2+) influx. We found that antagonism of N-methyl-D-aspartate (NMDA) receptors, but not 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl) propanoic acid or metabotropic glutamate receptors, decreased neuron death and prevented increases in [Ca(2+)](I) caused by PH/RW. Chelating extracellular Ca(2+) decreased PH/RW injury, but inhibiting L- and T-type voltage-gated Ca(2+) channels, K+ channels, Ca(2+) release from the endoplasmic reticulum, and reverse Na(+)/Ca(2+) exchange did not affect the Ca(2+) changes or cell death. We conclude that the mechanism of PH/RW neuronal injury in hippocampal slices primarily involves intracellular Ca(2+) accumulation mediated by NMDA receptors that activates necrotic, but not apoptotic processes.

Stoichiometry of N-methyl-D-aspartate receptors within the suprachiasmatic nucleus.

The circadian pacemaker within the suprachiasmatic nucleus (SCN) confers daily rhythms to bodily functions. In nature, the circadian clock will adopt a 24-h period by synchronizing to the solar light/dark cycle. This light entrainment process is mediated, in part, at glutamatergic synapses formed between retinal ganglion afferents and SCN neurons. N-methyl-D-aspartate receptors (NMDARs) located on SCN neurons gate light-induced phase resetting. Despite their importance in circadian physiology, little is known about their functional stoichiometry. We investigated the NR2-subunit composition with whole cell recordings of SCN neurons within the murine hypothalamic brain slice using a combination of subtype-selective NMDAR antagonists and voltage-clamp protocols. We found that extracellular magnesium ([Mg](o)) strongly blocks SCN NMDARs exhibiting affinities and voltage sensitivities associated with NR2A and NR2B subunits. These NMDAR currents were inhibited strongly by NR2B-selective antagonists, Ro 25-6981 (3.5 microM, 55.0 +/- 9.0% block; mean +/- SE) and ifenprodil (10 microM, 55.8 +/- 3.0% block). The current remaining showed decreased [Mg](o) affinities reminiscent of NR2C and NR2D subunits but was highly sensitive to [Zn](o), a potent NR2A blocker, showing a approximately 44.2 +/- 1.1% maximal inhibition at saturating concentrations with an IC(50) of 7.8 +/- 1.1 nM. Considering the selectivity, efficacy, and potency of the drugs used in combination with [Mg](o)-block characteristics of the NMDAR, our data show that both diheteromeric NR2B NMDARs and triheteromeric NR2A NMDARs (paired with an NR2C or NR2D subunits) account for the vast majority of the NMDAR current within the SCN.

Brain-derived neurotrophic factor and neurotrophin receptors modulate glutamate-induced phase shifts of the suprachiasmatic nucleus.

Light information reaches the suprachiasmatic nucleus (SCN) through a subpopulation of retinal ganglion cells. Previous work raised the possibility that brain-derived neurotrophic factor (BDNF) and its high-affinity tropomyosin-related receptor kinase may be important as modulators of this excitatory input into the SCN. In order to test this possibility, we used whole-cell patch-clamp methods to measure spontaneous excitatory currents in mouse SCN neurons. We found that the amplitude and frequency of these currents were increased by BDNF and decreased by the neurotrophin receptor inhibitor K252a. The neurotrophin also increased the magnitude of currents evoked by application of N-methyl-d-aspartate and amino-methyl proprionic acid. Next, we measured the rhythms in action potential discharge from the SCN brain slice preparation. We found that application of K252a dramatically reduced the magnitude of phase shifts of the electrical activity rhythm generated by the application of glutamate. By itself, BDNF caused phase shifts that resembled those produced by glutamate and were blocked by K252a. The results demonstrate that BDNF and neurotrophin receptors can enhance glutamatergic synaptic transmission within a subset of SCN neurons and potentiate glutamate-induced phase shifts of the circadian rhythm of neural activity in the SCN.

HIV protein, transactivator of transcription, alters circadian rhythms through the light entrainment pathway.

Patients infected with the human immunodeficiency virus (HIV), and other mammals infected with related lentiviruses, exhibit fatigue, altered sleep patterns, and abnormal circadian rhythms. A circadian clock in the hypothalamic suprachiasmatic nucleus (SCN) temporally regulates these functions in mammals. We found that a secretary HIV transcription factor, transactivator of transcription (Tat), resets the murine circadian clock, in vitro and in vivo, at clinically relevant concentrations (EC(50) = 0.31 nM). This effect of Tat occurs only during the subjective night, when N-methyl-D-aspartate (NMDA) receptor [D-2-amino-5-phosphonovaleric acid (0.1 mM)] and nitric oxide synthase (N(G)-nitro-L-arginine methyl ester, 0.1 mM) inhibitors block Tat-induced phase shifts. Whole cell recordings of SCN neurons within the brain slice revealed that Tat did not activate NMDA receptors directly but potentiated NMDA receptor currents through the enhancement of glutamate release. Consistent with this presynaptic mechanism, inhibitors of neurotransmission block Tat-induced phase shifts, such as tetrodotoxin (1 microM), tetanus toxin (1 microM), P/Q/N type-calcium channel blockers (1 microM omega-agatoxin IVA and 1 microM omega-conotoxin GIVA) and bafilomycin A(1) (1 microM). Thus the effect of Tat on the SCN may underlie lentiviral circadian rhythm dysfunction by operating as a disease-dependent modulator of light entrainment through the enhancement of excitatory neurotransmission.

Exotic dancing and health.

The health and safety of women who work as exotic dancers are firmly embedded within the social organization of the strip club and the broader social, economic and political context of the work of exotic dancing. Exotic dancers in this study expressed health concerns associated with: the effects of costuming and appearance requirements; dirty work environments; problems due to stigmatization, sexual harassment and assault; and police disinterest or victim blaming. The balance between benefits and hazards related to exotic dancing is influenced not only by the personal choices made by dancers, but also by the organization of the strip club and the broader context within which exotic dancing takes place.

Rate of heart failure and 1-year survival for older people receiving low-dose beta-blocker therapy after myocardial infarction.

BACKGROUND: Many older people do not receive beta-blocker therapy after myocardial infarction or receive doses lower than those tested in trials, perhaps because physicians fear that beta-blockers may precipitate heart failure. We examined the relation between use of beta-blockers, the dose used, and hospital admission for heart failure and 1-year survival in a cohort of all older patients surviving myocardial infarction in Ontario, Canada. METHODS: We collected data on a cohort of 13,623 patients aged 66 years or older who were discharged from hospital after a myocardial infarction and who did not receive beta-blocker therapy or received low, standard, or high doses. We used Cox's proportional-hazards models to study the association of dose with admission for heart failure and survival with adjustment for factors including age, sex, and comorbidity. FINDINGS: Among 8232 patients with no previous history of heart failure, dispensing of beta-blocker therapy was associated with a 43% reduction in subsequent admission for heart failure (adjusted risk ratio 0.57 [95% CI 0.48-0.69]) compared with patients not dispensed this therapy. Among the 4681 patients prescribed beta-blockers, the risk of admission was greater in the high-dose than in the low-dose group (1.53 [1.01-2.31]). Among all 13,623 patients in the cohort, 2326 (17.1%) died by 1 year. Compared with those not dispensed beta-blocker therapy, the adjusted risk ratio for mortality was lower for all three doses (low 0.40 [0.34-0.47], standard 0.36 [0.31-0.42], high 0.43 [0.33-0.56]). INTERPRETATION: Compared with high-dose beta-blocker therapy, low-dose treatment is associated with a lower rate of hospital admission for heart failure and has a similar 1-year survival benefit. Our findings support the need for a randomised controlled trial comparing doses of beta-blocker therapy in elderly patients.

Babes and boobs? analysis of JAMA cover art.

OBJECTIVE: To determine the representation of the sexes in JAMA cover art. DESIGN: Review of 50 consecutive issues. SETTING: JAMA, March 1997-March 1998. MAIN OUTCOME MEASURES: Numbers and nature of covers portraying men and women. RESULTS: Of the 50 covers, 34 depicted humans. 15 depicted women, 13 men, and 6 were of mixed or indeterminate sex. 11 pictures of women included a child and five included nudity. One cover showed a man with a child (not as a father) and none depicted nudity. Men were depicted exclusively in authoritative roles. CONCLUSIONS: Much of the cover art gives strong messages about sexual stereotypes that are inappropriate in modern society. JAMA should consider reviewing its policy for choosing cover art.

Age- and gender-related use of low-dose drug therapy: the need to manufacture low-dose therapy and evaluate the minimum effective dose.

OBJECTIVES: Low-dose drug therapy is promoted as a way to maximize benefit and minimize adverse drug effects when prescribing for older adults. This population-based study evaluates the age and sex-related use of two common therapies: thiazide diuretics, where evidence supports the use of low-dose therapy, and beta-blockers, where trials have not evaluated the minimum effective dose. DESIGN: Using linked administrative databases we identified all of the 120,613 persons dispensed a thiazide diuretic therapy and 12,908 myocardial infarction survivors dispensed beta-blocker therapy in Canada's largest province. We used logistic regression models to study the association of age and sex with dispensing of low-dose thiazide diuretic and beta-blocker therapy at doses lower than evaluated in trials. RESULTS: Of 120,613 older people dispensed a thiazide diuretic, 32,372 (26.8%) were dispensed a low dose. Patients 85 years of age or older, relative to the youngest group, were 30% more likely to be dispensed low-dose therapy (OR=1.31; 95% CI, 1.27 to 1.36; P < .001). Women were 8% more likely than men to be dispensed a low-dose thiazide diuretic (OR=1.08; 95% CI, 1.05 to 1.11; P < .001). Of 10,991 myocardial infarction survivors dispensed atenolol, metoprolol, propranolol, or timolol, 9458 (86.1%) were dispensed a lower-than-evaluated dose. Patients 85 years of age or older, relative to those in the youngest group, were more than twice as likely to be dispensed a lower-than-evaluated beta-blocker therapy dose (OR=2.28; 95% CI, 1.74 to 3.04; P < .001). No difference was noted in the use of beta-blocker therapy dose by sex (OR=1.0; 95% CI, .89 to 1.15; P = .95). CONCLUSIONS: Low-dose thiazide diuretic therapy prescribed widely to older people, particularly those of advanced age and women. The vast majority of myocardial infarction survivors were dispensed beta-blocker therapy at lower-than-evaluated doses. These findings highlight the need to manufacture low-dose thiazide diuretic therapy and to evaluate the minimum effective dose of beta-blocker therapy.

Social and cultural vulnerability to sexually transmitted infection: the work of exotic dancers.

This article examines the social and cultural factors that influence the vulnerability of female exotic dancers to sexually transmitted infections. Results are based on a qualitative, exploratory study using observations in 10 clubs and in-depth interviews with 30 dancers in southern Ontario. The social and cultural context within which exotic dancing takes place contributes to a chronic state of sexual harassment and sexual assault in the strip clubs. Women are pressured by economics and by their customers to engage in sex for pay. The defence mechanisms that some women use to deal with these work conditions also contribute to women's vulnerability. The social structure of strip clubs and their policies toward employees and customers can either reduce or exacerbate the vulnerability of dancers. Workplace policies and health and safety standards appear to be the most effective ways to decrease the vulnerability of dancers. Public health units can work with employers and dancers to establish workplace policies and programmes that contribute to the health and wellbeing of dancers.

Novel terpenoid-type quinones isolated from Pycnanthus angolensis of potential utility in the treatment of type 2 diabetes.

Using an ethnomedical-based drug discovery program, two previously unknown compounds (SP-18904 and SP-18905) from Pycnanthus angolensis were isolated that lower glucose concentrations in mouse models of type 2 diabetes. SP-18904 and SP-18905 are terpenoid-type quinones that significantly lowered plasma glucose concentration (p <.05) when given orally to either ob/ob or db/db mice, both of which are hyperglycemic and hyperinsulinemic. The antihyperglycemic actions of SP-18904 and SP-18905 were associated with significant decreases in plasma insulin concentrations (p <.05), suggesting that both compounds lowered glucose by enhancing insulin-mediated glucose uptake. This was supported by the insulin suppression test in ob/ob mice. Studies in hyperglycemic, insulin-deficient mice and in vitro experiments on 3T3-L1 adipocytes further supported this conclusion. As such, these two terpenoid-type quinones represent a new class of compounds of potential use in the treatment of type 2 diabetes.

Use of beta-blocker therapy in older patients after acute myocardial infarction in Ontario.

BACKGROUND: Despite its proven efficacy, beta-blocker therapy remains underused in elderly patients after myocardial infarction (MI). The objectives of this study were to identify undertreated groups of seniors and to determine whether older and frailer patients are being selectively dispensed low-dose beta-blocker therapy. METHODS: From a comprehensive hospital discharge database, all people aged 66 years or more in Ontario who survived an acute MI between April 1993 and March 1995 were identified and classified into those who did not receive beta-blocker therapy and those dispensed low, standard or high doses of this agent. Logistic regression models were used to study the effect of age, sex, comorbidity, potential contraindications to beta-blocker therapy and residence in a long-term-care facility on the odds of not being dispensed a beta-blocker. Among beta-blocker users, the odds of being dispensed low relative to standard or high doses of this agent were evaluated. RESULTS: Of the 15,542 patients, 7549 (48.6%) were not dispensed a beta-blocker. Patients 85 years of age or more were at greater risk of not receiving beta-blocker therapy (adjusted odds ratio [OR] 2.8, 95% confidence interval [CI] 2.5-3.2) than were those 66 to 74 years. Having a Charlson comorbidity index of 3 or greater was associated with an increased risk of not receiving beta-blocker therapy (adjusted OR 1.5, 95% CI 1.3-1.8) compared with having lower comorbidity scores. Patients who resided in a long-term-care facility were at increased risk of not being prescribed beta-blocker therapy (adjusted OR 2.6, 95% CI 2.0-3.4). Among the 5453 patients with no identifiable contraindication to beta-blocker therapy, women were significantly less likely than men to receive this agent (p = 0.005). Of the 6074 patients who received beta-blockers, 2248 (37.0%) were dispensed low-dose therapy. Patients aged 85 years or more had an increased risk of being dispensed low-dose therapy (adjusted OR 1.6, 95% CI 1.3-2.0) compared with those aged 66 to 74 years. Compared with those who had the lowest comorbidity scores, patients with the highest comorbidity scores were more likely to be dispensed low-dose beta-blocker therapy (adjusted OR 1.3, 95% CI 1.0-1.8). INTERPRETATION: Almost half of Ontario patients aged 66 or more who survived an MI, particularly those who were older or frailer, did not receive beta-blocker therapy. Among those dispensed beta-blocker therapy, older and frailer patients were more frequently dispensed low-dose therapy.

Reporting of gender-related information in clinical trials of drug therapy for myocardial infarction.

BACKGROUND: Concern has been expressed that women are not adequately represented in clinical trials evaluating treatments for medical conditions they commonly experience. This study was designed to assess the reporting of data on women in recently published trials of drug therapy for myocardial infarction, including those funded by an agency with a gender-related policy. METHODS: All randomized controlled trials and meta-analyses of drug therapies for myocardial infarction published in The New England Journal of Medicine, The Lancet, The Journal of the American Medical Association, the Annals of Internal Medicine and the British Medical Journal from January 1992 to December 1996 were evaluated. On preliminary review 102 articles met the inclusion criteria; these were reviewed in detail, and 59 were excluded. Two reviewers independently extracted gender-related information from the 43 articles; discrepancies were resolved by consensus. RESULTS: Women presented up to 48% of the trial participants (mean 24.1%). In the trials funded by an agency with a gender-related policy, only 16.8% of participants, on average, were women. Of the 43 articles in the sample, only 14 (32%) provided gender-related results. Funding from an agency with gender-related policy did not affect the reporting of gender-related information. Subgroup analyses were provided for 14 (32%) of the 43 trials, including 2 (29%) of 7 trials funded by an agency with a gender-related policy. Of the 12 trials that included interaction analyses (excluding the 2 trials in which secondary analyses were conducted specifically to identify differences between women and men), 7 (58%) conducted an interaction analysis to determine if women responded differently than men; for one of these the interaction analysis was for a secondary outcome measure (drug safety). Only 5 (12%) of the 43 articles mentioned the differences between men and women in the Discussion section; 2 of these were studies that used secondary analyses to examine sex differences. Of the 5, only 1 was funded by an agency with a gender-related policy. INTERPRETATION: Women were poorly represented in the randomized controlled trials in this sample, regardless of whether the trials were funded by an agency with a gender-related policy. Structured reporting of gender-related information for clinical trials may improve the quality of information available about women and therefore facilitate the application of research findings to the care of women.

Chemical induction of thymomas in AKR mice: interaction of chemical carcinogens and endogenous murine leukemia viruses. Comparison of N-methyl-N-nitrosourea and methyl methanesulphonate.

The time course of development of thymic lymphoma, which occurs spontaneously in mice of the AKR strain, is accelerated by the methylating agents N-methyl-N-nitrosourea (MNU) and methyl methanesulphonate (MMS). Since MNU is a potent mutagen inducing G----A transition mutations and MMS a relatively weak mutagen, it was of interest to examine the genetic alterations associated with each class of the chemically induced tumors and to compare these alterations with those found in the spontaneous tumors. The same spectrum of genetic alterations was found for MMS-induced and spontaneous thymomas. Both showed rearrangements of c-myc and Pim-1 genes that appeared to result from integration of recombinant mink cytopathic focus-forming (MCF) proviruses but failed to reveal evidence for activation of ras oncogenes, either by DNA transfection experiments or by hybridization of DNA to specific oligonucleotide probes. Some alteration in c-myc and Pim-1 genes were also found in MNU-induced tumors, but, mainly, these involved integration of ecotropic-like rather than recombinant MCF viruses. Furthermore, MNU-induced tumors frequently (in 24% of thymomas) contained G----A transition mutations, activating the Ki-ras oncogene at codon 12 position 2. Another feature that distinguishes the MNU-induced tumors from those occurring in untreated and MMS-treated mice was the consistently high level of c-myc mRNA that occurred in the absence of c-myc gene rearrangement. Taken together, the data indicate that the mechanisms of development of tumors following treatment with MNU and MMS are distinct, and that the effect of MMS is probably to speed up the process of viral leukemogenesis.

Deterrence in the workplace: perceived certainty, perceived severity, and employee theft.

The phenomenon of employee theft is examined empirically, utilizing a deterrence paradigm. Employees selected randomly from three different industry sectors and metropolitan areas were asked to self-report their involvement in a number of property theft activities within the employment setting. Using a weighted least-squares logit regression analysis, the study found that the perception of both the certainty and severity of organizational sanctions were related to employee theft. Males reported more theft than did females, but contrary to previous research, no gender/certainty or gender/severity interactions were observed. The best-fit model did, however, contain two significant first-order interactions: age/certainty and age/severity. These interactions strongly suggest that younger employees are not as deterrable as their older peers, especially under conditions of both high certainty and high severity of punishment. While a number of possible explanations might account for differential deterrability according to age, a commitment to or stakes in conformity explanation is proposed.

Evidence that histamine and carbachol may open the same ion channels in longitudinal smooth muscle of guinea-pig ileum.

1. Membrane potential was recorded intracellularly by micro-electrode in separated longitudinal muscle of guinea-pig ileum. Electrotonic potentials were evoked in longitudinal strips by passing current between large external electrodes in the partition chamber.2. Histamine increased the frequency of action potential discharge at low concentrations and depolarized the membrane. At higher concentrations it caused substantial depolarization and action potential discharge was abolished. Carbachol had similar actions but the maximal depolarization by carbachol (using 10(-4)m) was some 4-5 mV greater than maximal depolarization by histamine (using 10(-4)m).3. The change in size of evoked electrotonic potentials was used to estimate the effects of carbachol and histamine on the conductance of the smooth muscle membrane. The equilibrium potentials for histamine and carbachol depolarizations were estimated from their relative effects on potential and conductance and were found to be not significantly different; measurements of the effects on conductance showed that 10(-4)m-histamine increased conductance about 8-fold whilst 10(-4)m-carbachol had a much greater effect on conductance. This difference could explain the differing maximal depolarizing effects of these agents if both were assumed to open channels having the same ionic selectivity (i.e. equilibrium potential).4. The efflux of (42)K was studied in separated strips of longitudinal ileal muscle from guinea-pig. In the presence of a concentration of carbachol (2 x 10(-5)m or 10(-4)m) having a maximal effect on (42)K efflux rate, histamine (10(-4)m) did not increase efflux further although 120 mm-potassium did so. Experiments with the irreversible muscarinic receptor blocker, propylbenzilylcholine mustard, indicated that the number of muscarinic receptors did not limit the (42)K efflux response to carbachol and it was suggested that the response was limited by the availability of ion channels which could be opened by activated muscarinic receptors.5. Contractions to histamine and carbachol in 120 mm-potassium depolarizing solution were followed upon washing by a relaxation below basal tension. Carbachol, but not histamine, showed a pronounced and long lasting secondary contraction following this relaxation.6. These results are consistent with the idea that activated histamine and activated muscarinic receptors open the same ion channels in the smooth muscle membrane to produce depolarization, increased action potential discharge and contraction, although muscarinic receptors can open more of these. However, there was evidence that the opening of these channels is not the only pathway between receptor activation and contraction.