Impact of COVID-19 pandemic on the management of nonculprit lesions in patients presenting with ST-elevation myocardial infarction: Outcomes from the pan-London heart attack centers.

BACKGROUND: The impact of COVID-19 on the diagnosis and management of nonculprit lesions remains unclear. OBJECTIVES: This study sought to evaluate the management and outcomes of patients with nonculprit lesions during the COVID-19 pandemic. METHODS: We conducted a retrospective observational analysis of consecutive primary percutaneous coronary intervention (PPCI) pathway activations across the heart attack center network in London, UK. Data from the study period in 2020 were compared with prepandemic data in 2019. The primary outcome was the rate of nonculprit lesion percutaneous coronary intervention (PCI) and secondary outcomes included major adverse cardiovascular events. RESULTS: A total of 788 patients undergoing PPCI were identified, 209 (60%) in 2020 cohort and 263 (60%) in 2019 cohort had nonculprit lesions (p = .89). There was less functional assessment of the significance of nonculprit lesions in the 2020 cohort compared to 2019 cohort; in 8% 2020 cohort versus 15% 2019 cohort (p = .01). There was no difference in rates of PCI for nonculprit disease in the 2019 and 2020 cohorts (31% vs 30%, p = .11). Patients in 2020 cohort underwent nonculprit lesion PCI sooner than the 2019 cohort (p < .001). At 6 months there was higher rates of unplanned revascularization (4% vs. 2%, p = .05) and repeat myocardial infarction (4% vs. 1%, p = .02) in the 2019 cohort compared to 2020 cohort. CONCLUSION: Changes to clinical practice during the COVID-19 pandemic were associated with reduced rates of unplanned revascularization and myocardial infarction at 6-months follow-up, and despite the pandemic, there was no difference in mortality, suggesting that it is not only safe but maybe more efficacious.

Role of reactive oxygen species and sulfide-quinone oxoreductase in hydrogen sulfide-induced contraction of rat pulmonary arteries.

Application of H2S ("sulfide") elicits a complex contraction in rat pulmonary arteries (PAs) comprising a small transient contraction (phase 1; Ph1) followed by relaxation and then a second, larger, and more sustained contraction (phase 2; Ph2). We investigated the mechanisms causing this response using isometric myography in rat second-order PAs, with Na2S as a sulfide donor. Both phases of contraction to 1,000 µM Na2S were attenuated by the pan-PKC inhibitor Gö6983 (3 µM) and by 50 µM ryanodine; the Ca2+ channel blocker nifedipine (1 µM) was without effect. Ph2 was attenuated by the mitochondrial complex III blocker myxothiazol (1 µM), the NADPH oxidase (NOX) blocker VAS2870 (10 µM), and the antioxidant TEMPOL (3 mM) but was unaffected by the complex I blocker rotenone (1 µM). The bath sulfide concentration, measured using an amperometric sensor, decreased rapidly following Na2S application, and the peak of Ph2 occurred when this had fallen to ~50 µM. Sulfide caused a transient increase in NAD(P)H autofluorescence, the offset of which coincided with development of the Ph2 contraction. Sulfide also caused a brief mitochondrial hyperpolarization (assessed using tetramethylrhodamine ethyl ester), followed immediately by depolarization and then a second more prolonged hyperpolarization, the onset of which was temporally correlated with the Ph2 contraction. Sulfide application to cultured PA smooth muscle cells increased reactive oxygen species (ROS) production (recorded using L012); this was absent when the mitochondrial flavoprotein sulfide-quinone oxoreductase (SQR) was knocked down using small interfering RNA. We propose that the Ph2 contraction is largely caused by SQR-mediated sulfide metabolism, which, by donating electrons to ubiquinone, increases electron production by complex III and thereby ROS production.

Prognostic significance of computed tomography criteria for pulmonary veno-occlusive disease in systemic sclerosis-pulmonary arterial hypertension.

Objectives: SSc-pulmonary arterial hypertension (SSc-PAH) is associated with worse response to therapy and survival when compared with idiopathic PAH. It is suggested that the vasculopathy in SSc may involve postcapillary pulmonary venules resulting in pulmonary veno-occlusive disease (PVOD). This may underlie the lower gas transfer and worse outcome on therapy. We sought to test whether CT signs of PVOD (CTS-PVOD) were frequent in SSc-PAH and whether they were associated with pulmonary oedema on therapy and worse survival. Methods: CT thorax of 66 SSc patients with precapillary pulmonary hypertension (PH) were blindly scored by two radiologists for CTS-PVOD (⩽1 or ⩾ 2). Case note and radiograph review determined the presence of pulmonary oedema on therapy. Results: Fifty-nine patients (89%) had ⩽1 CTS-PVOD and only 7 (11%) had ⩾2 CTS-PVOD. Pulmonary oedema on therapy was relatively common in those with ⩾2 CTS-PVOD. On univariate analysis ⩾2 CTS-PVOD were associated with a trend towards worse survival. Conclusion: CTS-PVOD were less frequent in this SSc-PAH cohort than in previous reports but the presence of at least two of these signs is associated with pulmonary oedema on therapy and a trend towards worse survival on univariate analysis.

A preliminary study of osmotic dehydration in zebrafish embryos: Implications for vitrification and ultra-fast laser warming.

To date, traditional cryopreservation techniques have not been amenable to zebrafish (Danio rerio) embryos, due in part to their large yolky eggs, which have a low surface to volume ratio and limited permeability to water and cryoprotectants. However, recent vitrification and ultra-rapid warming studies in mice have demonstrated successful preservation by dehydrating 85% or more of their total water content. We hypothesized that this approach may help overcome the barriers to embryo cryopreservation among D. rerio. The purpose of this study was to determine the osmotic tolerance limit of D. rerio embryos under conditions relevant to cryopreservation. We found that embryos undergoing gastrulation (30%-70% epiboly) were particularly sensitive to osmotic dehydration/rehydration. By contrast, a subset of embryos dehydrated during or after segmentation (20-22 somite, prim 5) survived 3 h in a 2 M sucrose solution but exhibit developmental delay, edema and trunk necrosis 2-4 days post-treatment.

A frontal swelling with a cautionary tale.

Frontal sinus mucoceles are the most common paranasal mucoceles. They consist of sterile mucus and shed cells and form due to inflammatory changes or chronic nasofrontal duct obstruction. Coincident infection and expansile growth can lead to specific clinical features dependent upon the location of the lesion and the degree of spread. We present a case of a 56-year-old lady with a radiological diagnosis of a frontal sinus mucocele causing anterior dehiscence of her frontal cortex. She underwent incision and drainage of a frontal swelling misdiagnosed as an infected sebaceous cyst. The case emphasises the importance of correlating features in the patient history and previous investigations with presenting findings.

Hypoxic pulmonary vasoconstriction in the absence of pretone: essential role for intracellular Ca2+ release.

Hypoxic pulmonary vasoconstriction (HPV) maintains blood oxygenation during acute hypoxia but contributes to pulmonary hypertension during chronic hypoxia. The mechanisms of HPV remain controversial, in part because HPV is usually studied in the presence of agonist-induced preconstriction ('pretone'). This potentiates HPV but may obscure and distort its underlying mechanisms. We therefore carried out an extensive assessment of proposed mechanisms contributing to HPV in isolated intrapulmonary arteries (IPAs) in the absence of pretone by using a conventional small vessel myograph. Hypoxia elicited a biphasic constriction consisting of a small transient (phase 1) superimposed upon a sustained (phase 2) component. Neither phase was affected by the L-type Ca2+ channel antagonists diltiazem (10 and 30 µm) or nifedipine (3 µm). Application of the store-operated Ca2+ entry (SOCE) blockers BTP2 (10 µm) or SKF96365 (50 µm) attenuated phase 2 but not phase 1, whereas a lengthy (30 min) incubation in Ca2+-free physiological saline solution similarly reduced phase 2 but abolished phase 1. No further effect of inhibition of HPV was observed if the sarco/endoplasmic reticulum Ca2+-ATPase inhibitor cyclopiazonic acid (30 µm) was also applied during the 30 min incubation in Ca2+-free physiological saline solution. Pretreatment with 10 µm ryanodine and 15 mm caffeine abolished both phases, whereas treatment with 100 µm ryanodine attenuated both phases. The two-pore channel blocker NED-19 (1 µm) and the nicotinic acid adenine dinucleotide phosphate (NAADP) antagonist BZ194 (200 µm) had no effect on either phase of HPV. The lysosomal Ca2+-depleting agent concanamycin (1 µm) enhanced HPV if applied during hypoxia, but had no effect on HPV during a subsequent hypoxic challenge. The cyclic ADP ribose antagonist 8-bromo-cyclic ADP ribose (30 µm) had no effect on either phase of HPV. Neither the Ca2+-sensing receptor (CaSR) blocker NPS2390 (0.1 and 10 µm) nor FK506 (10 µm), a drug which displaces FKBP12.6 from ryanodine receptor 2 (RyR2), had any effect on HPV. HPV was virtually abolished by the rho kinase blocker Y-27632 (1 µm) and attenuated by the protein kinase C inhibitor Gö6983 (3 µm). Hypoxia for 45 min caused a significant increase in the ratio of oxidised to reduced glutathione (GSSG/GSH). HPV was unaffected by the NADPH oxidase inhibitor VAS2870 (10 µm), whereas phase 2 was inhibited but phase 1 was unaffected by the antioxidants ebselen (100 µm) and TEMPOL (3 mm). We conclude that both phases of HPV in this model are mainly dependent on [Ca2+]i release from the sarcoplasmic reticulum. Neither phase of HPV requires voltage-gated Ca2+ entry, but SOCE contributes to phase 2. We can detect no requirement for cyclic ADP ribose, NAADP-dependent lysosomal Ca2+ release, activation of the CaSR, or displacement of FKBP12.6 from RyR2 for either phase of HPV. Sustained HPV is associated with an oxidising shift in the GSSG/GSH redox potential and is inhibited by the antioxidants ebselen and TEMPOL, consistent with the concept that it requires an oxidising shift in the cell redox state or the generation of reactive oxygen species.

The Impact of a National Cyberattack Affecting Clinical Trials: The Cancer Trials Ireland Experience.

PURPOSE: Cyberattacks are increasing in health care and cause immediate disruption to patient care, have a lasting impact, and compromise scientific integrity of affected clinical trials. On the May 14, 2021, the Irish health service was the victim of a nationwide ransomware attack. Patient care was disrupted across 4,000 locations, including 18 cancer clinical trials units associated with Cancer Trials Ireland (CTI). This report analyses the impact of the cyberattack on the organization and proposes steps to mitigate the impact of future cyberattacks. METHODS: A questionnaire was distributed to the units within the CTI group; this examined key performance indicators for a period of 4 weeks before, during, and after the attack, and was supplemented by minutes of weekly conference call with CTI units to facilitate information sharing, accelerate mitigation, and support affected units. A total of 10 responses were returned, from three private and seven public hospitals. RESULTS: The effect of the attack on referrals and enrollment to trials was marked, resulting in a drop of 85% in referrals and 55% in recruitment before recovery. Radiology, radiotherapy, and laboratory systems are heavily reliant on information technology systems. Access to all was affected. Lack of preparedness was highlighted as a significant issue. Of the sites surveyed, two had a preparedness plan in place before the attack, both of these being private institutions. Of the eight institutions where no plan was in place, three now have or are putting a plan in place, whereas no plan is in place at the five remaining sites. CONCLUSION: The cyberattack had a dramatic and sustained impact on trial conduct and accrual. Increased cybermaturity needs to be embedded in clinical trial logistics and the units conducting them.

Peroxisome proliferator-activated receptor-ß/δ, the acute signaling factor in prostacyclin-induced pulmonary vasodilation.

As powerful vasodilators, prostacyclin analogues are presently the mainstay in the treatment of severe pulmonary arterial hypertension. Although the hemodynamic effects of prostacyclin analogues are well known, the molecular mechanism of their acute effects on pulmonary vascular tone and systemic vascular tone remains poorly understood. Peroxisome proliferator-activated receptor-ß/δ (PPARß/δ) was previously identified as a putative receptor responsible for the modulation of target gene expression in response to prostacyclin analogues. The present study investigated the signaling pathway of prostacyclin in human pulmonary arterial smooth muscle cells (PASMCs), and sought to define the role of PPARß/δ in the acute vasodilating effect. In human PASMCs, prostacyclin rapidly activated TWIK-related acid-sensitive K channel 1 (TASK-1) and calcium-dependent potassium channels (K(Ca)). This pathway was mediated via the prostanoid I receptor-protein kinase A pathway. The silencing of PPARß/δ demonstrated that the downstream K(Ca) activation was exclusively dependent on PPARß/δ signaling, whereas the activation of TASK-1 was not. In addition, the PPARß/δ-induced activation of K(Ca) was independent of NO. The acute prostacyclin-induced K(Ca) activation is critically dependent on PPARß/δ as a rapid signaling factor. This accounts in part for the vasodilating effect of prostacyclin in pulmonary arteries, and provides insights into a new molecular explanation for the effects of prostanoids.

Time to internal fixation of femoral neck fractures in patients under sixty years--does this matter in the development of osteonecrosis of femoral head?

PURPOSE: Osteonecrosis of femoral head remains a major complication of femoral neck fractures. It has been postulated that early internal fixation drastically reduces the incidence of osteonecrosis of the femoral head. However, there is a paucity of literature looking at the effect of time delay to internal fixation on the development of this late complication. In this study, we aim to assess the effect of time delay and method of internal fixation on the development of osteonecrosis in those less than 60 years of age. METHODS: We retrospectively analysed 92 patients less than 60 years of age who presented with intracapsular neck of femur fractures that underwent internal fixation between 1999 and 2009. RESULTS: Of the 92 intracapsular fractures, 50 underwent fixation using cannulated screws, 32 using a dynamic hip screw, and ten using a dynamic hip screw with a derotation screw. In total, 13 patients (14.1 %) developed osteonecrosis of the femoral head, the highest incidence being in the cannulated screw fixation group with an osteonecrosis rate of 24 %. We did not find the time delay to internal fixation to be a significant predictor of the development of osteonecrosis. CONCLUSION: Our study demonstrated that the method of internal fixation rather than delay in internal fixation was more predictive of osteonecrosis of the femoral head. We did not find support to the current belief that early surgical fixation of neck of femur fractures reduces the risk of osteonecrosis in patients less than 60 years.

Identification of adult mineralized tissue zebrafish mutants.

Zebrafish craniofacial, skeletal, and tooth development closely resembles that of higher vertebrates. Our goal is to identify viable adult zebrafish mutants that can be used as models for human mineralized craniofacial, dental, and skeletal system disorders. We used a large-scale forward-genetic chemical N-ethyl-nitroso-urea mutagenesis screen to identify 17 early lethal homozygous recessive mutants with defects in craniofacial cartilage elements, and 7 adult homozygous recessive mutants with mineralized tissue phenotypes including craniofacial shape defects, fused sutures, dysmorphic or missing skeletal elements, scoliosis, and neural arch defects. One mutant displayed both an early lethal homozygous phenotype and an adult heterozygous phenotype. These results extend the utility of the zebrafish model beyond the embryo to study human bone and cartilage disorders.

Key role of the RhoA/Rho kinase system in pulmonary hypertension.

Pulmonary hypertension (PH) is a general term comprising a spectrum of pulmonary hypertensive disorders which have in common an elevation of mean pulmonary arterial pressure (mPAP). The prototypical form of the disease, termed pulmonary arterial hypertension (PAH), is a rare but lethal syndrome with a complex aetiology characterised by increased pulmonary vascular resistance (PVR) and progressive elevation of mPAP; patients generally die from heart failure. Current therapies are inadequate and median survival is less than three years. PH due to chronic hypoxia (CH) is a condition separate from PAH and is strongly associated with chronic obstructive pulmonary disease (COPD). An early event in the pathogenesis of this form of PH is hypoxic pulmonary vasoconstriction (HPV), an acute homeostatic process that maintains the ventilation-perfusion ratio during alveolar hypoxia. The mechanisms underlying HPV remain controversial, but RhoA/Rho kinase (ROK)-mediated Ca²+-sensitisation is considered important. Increasing evidence also implicates RhoA/ROK in PASMC proliferation, inflammatory cell recruitment and the regulation of cell motility, all of which are involved in the pulmonary vascular remodelling occurring in all forms of PH. ROK is therefore a potential therapeutic target in treating PH of various aetiologies. Here, we examine current concepts regarding the aetiology of PAH and also PH due to CH, focusing on the contribution that RhoA/ROK-mediated processes may make to their development and on ROK inhibitors as potential therapies.

Scoping Review: Suicide Specific Intervention Programmes for People Experiencing Homelessness.

BACKGROUND: The homeless population are among the most vulnerable groups to experience suicide ideation and behavior. Several studies have shown that people who are homeless experience more significant suicidal ideation and behavior than the general population. However, there is limited information about what suicide interventions exist, to what extent they are grounded in robust research, and which intervention components effectively reduce suicidal ideation and behavior in the homeless community. This research aimed to characterise the current evidence base in the area of suicide prevention for homeless individuals. METHODS: A scoping review guided by Arksey and O'Malley's five-stage framework was conducted and a narrative synthesis was performed. Pubmed, EMBASE, PsychInfo, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Open Grey, and Bielefeld Academic Search Engine were searched up to 8 May 2020. RESULTS: A total of 3209 records were identified through database and grey literature searching. Three studies are included in this review. Key outcomes identify suicide intervention prevention programmes; similarities and differences across interventions, and examples of staff training. A quality review of the studies was completed. CONCLUSION: A stark gap in the evidence of suicide specific prevention interventions targeted at homeless populations.

Cardiac arrest, chronic total occlusion, and occluded stent in a 16-year-old boy with Kawasaki disease: a case report.

BACKGROUND: Kawasaki disease is the leading cause of premature coronary artery disease in developed countries. As such, patients may require revascularisation as children. However, there are no randomized data guiding treatment so this must be individualized. This case report describes the decision-making in a young patient requiring revascularization who had already suffered stent occlusion. CASE SUMMARY: Our patient, a 16-year-old boy with Kawasaki disease, presented with cardiac arrest during exercise. Coronary angiography showed that a proximal left anterior descending artery stent implanted at the age of 8 years had occluded some time ago and his right coronary artery was also chronically occluded. He has discussed in several Heart Team meetings and with international colleagues and a consensus reached to revascularize him surgically. DISCUSSION: It is vital that young patients with complex coronary disease are discussed in an extensive multidisciplinary setting to determine the most suitable means of treatment. The previously occluded stent was crucial in the individualized decision-making in this patient.

COVID-19 pandemic and STEMI: pathway activation and outcomes from the pan-London heart attack group.

OBJECTIVES: To understand the impact of COVID-19 on delivery and outcomes of primary percutaneous coronary intervention (PPCI). Furthermore, to compare clinical presentation and outcomes of patients with ST-segment elevation myocardial infarction (STEMI) with active COVID-19 against those without COVID-19. METHODS: We systematically analysed 348 STEMI cases presenting to the PPCI programme in London during the peak of the pandemic (1 March to 30 April 2020) and compared with 440 cases from the same period in 2019. Outcomes of interest included ambulance response times, timeliness of revascularisation, angiographic and procedural characteristics, and in-hospital clinical outcomes RESULTS: There was a 21% reduction in STEMI admissions and longer ambulance response times (87 (62-118) min in 2020 vs 75 (57-95) min in 2019, p<0.001), but that this was not associated with a delays in achieving revascularisation once in hospital (48 (34-65) min in 2020 vs 48 (35-70) min in 2019, p=0.35) or increased mortality (10.9% (38) in 2020 vs 8.6% (38) in 2019, p=0.28). 46 patients with active COVID-19 were more thrombotic and more likely to have intensive care unit admissions (32.6% (15) vs 9.3% (28), OR 5.74 (95%CI 2.24 to 9.89), p<0.001). They also had increased length of stay (4 (3-9) days vs 3 (2-4) days, p<0.001) and a higher mortality (21.7% (10) vs 9.3% (28), OR 2.72 (95% CI 1.25 to 5.82), p=0.012) compared with patients having PPCI without COVID-19. CONCLUSION: These findings suggest that PPCI pathways can be maintained during unprecedented healthcare emergencies but confirms the high mortality of STEMI in the context of concomitant COVID-19 infection characterised by a heightened state of thrombogenicity.

Propagation of human enteropathogens in constructed horizontal wetlands used for tertiary wastewater treatment.

Constructed subsurface flow (SSF) and free-surface flow (FSF) wetlands are being increasingly implemented worldwide into wastewater treatments in response to the growing need for microbiologically safe reclaimed waters, which is driven by an exponential increase in the human population and limited water resources. Wastewater samples from four SSF and FSF wetlands in northwestern Ireland were tested qualitatively and quantitatively for Cryptosporidium spp., Giardia duodenalis, and human-pathogenic microsporidia, with assessment of their viability. Overall, seven species of human enteropathogens were detected in wetland influents, vegetated areas, and effluents: Cryptosporidium parvum, C. hominis, C. meleagridis, C. muris, G. duodenalis, Encephalitozoon hellem, and Enterocytozoon bieneusi. SSF wetland had the highest pathogen removal rate (i.e., Cryptosporidium, 97.4%; G. duodenalis, 95.4%); however, most of these values for FSF were in the negative area (mean, -84.0%), meaning that more pathogens were discharged by FSF wetlands than were delivered to wetlands with incoming wastewater. We demonstrate here that (i) the composition of human enteropathogens in wastewater entering and leaving SSF and FSF wetlands is highly complex and dynamic, (ii) the removal and inactivation of human-pathogenic microorganisms were significantly higher at the SSF wetland, (iii) FSF wetlands may not always provide sufficient remediation for human enteropathogens, (iv) wildlife can contribute a substantial load of human zoonotic pathogens to wetlands, (v) most of the pathogens discharged by wetlands were viable, (vi) large volumes of wetland effluents can contribute to contamination of surface waters used for recreation and drinking water abstraction and therefore represent a serious public health threat, and (vii) even with the best pathogen removal rates achieved by SSF wetland, the reduction of pathogens was not enough for a safety reuse of the reclaimed water. To our knowledge, this is the first report of C. meleagridis from Ireland.

Fate of Cryptosporidium parvum and Cryptosporidium hominis oocysts and Giardia duodenalis cysts during secondary wastewater treatments.

This study investigates the fate of Cryptosporidium parvum and C. hominis oocysts and Giardia duodenalis cysts at four Irish municipal wastewater treatment plants (i.e., Plant A, B, C, and D) that utilize sludge activation or biofilm-coated percolating filter systems for secondary wastewater treatment. The fate of these pathogens through the sewage treatment processes was determined based on their viable transmissive stages, i.e., oocysts for Cryptosporidium and cysts for Giardia. Analysis of final effluent indicated that over 97% of viable oocysts and cysts were eliminated, except at Plant C, which achieved only 64% of oocyst removal. A significant correlation between the removal of oocysts and cysts was found at Plants A, B, and D (R = 0.98, P < 0.05). All sewage sludge samples were positive for C. parvum and C. hominis, and G. duodenalis, with maximum concentrations of 20 oocysts and eight cysts per gram in primary sludge indicating the need for further sludge sanitization treatments. This study provides evidence that C. parvum and C. hominis oocysts and G. duodenalis cysts are present throughout the wastewater processes and in end-products, and can enter the aquatic environment with consequent negative implications for public health.

Embryonic heat shock reveals latent hsp90 translation in zebrafish (Danio rerio).

There is increasing evidence that more genetic variation is present among metazoans than is normally expressed in the phenotype, due in part to the canalization of development. Among teleosts (as in other vertebrates), this genetic variation is often expressed as phenotypic change in response to environmental cues. Using embryonic zebrafish (Danio rerio), this 'hidden' variation is explored in the context of environmental stress by investigating the activity of heat shock protein-90 (HSP90), a cytosolic chaperone that interacts with transcription factors to mediate multiple developmental pathways. Following a 37 degrees C heat shock during early somitogenesis (1 hour heat shock, targeting 2-14 somite stages), phenotypic variability was expressed in the lower trunk and tail bud regions, where somite development was reduced or ceased prematurely. In situ hybridization showed that hsp90 was localized to this caudal region 16 hours after heat shock, indicating its potential to coordinate somitic fate. By following transcription and translation of this chaperone, we show that 24 hours following heat shock zebrafish embryos express a protein signature which reflects the RNA message. However, by 48 hours, message and protein are uncoupled; while endogenous gene expression is downregulated, heat-shocked embryos express a discrete segmented protein pattern within the trunk, suggesting regulation of transcription and of translation in response to environmental stress.

A role for voltage-gated, but not Ca2+-activated, K+ channels in regulating spontaneous contractile activity in myometrium from virgin and pregnant rats.

The roles of voltage-gated (K(V)) and large conductance Ca2+-activated K+ (BK(Ca)) channels in regulating basal contractility in myometrial smooth muscle are unresolved. The aim of this study was to determine the effects of inhibition of these channels on spontaneous rhythmic contraction in myometrial strips from four groups of rats: nonpregnant and during early (day 7), mid- (day 14), and late (day 21) pregnancy. BK(Ca) channels were inhibited using iberiotoxin (1-100 nM), paxilline (1-10 microM) or penitrem A (1-500, or 3000 nM); K(V) channels were inhibited using tetraethylammonium (TEA; 1-10 mM) and/or 4-aminopyridine (4-AP; 1-5 mM). Contractility was assessed as mean integral tension (MIT). Time/vehicle controls were also performed. None of the selective BK(Ca) channel inhibitors significantly affected contractility in myometrial strips from either nonpregnant or pregnant animals. 4-AP caused concentration-dependent increases in MIT in myometrium in all four groups. TEA (5 and 10 mM) significantly increased MIT in myometrium from nonpregnant, and mid- and late pregnant rats, but not in myometrium from early pregnant rats. TEA and 4-AP still caused an increase in MIT following treatment with 3000 nM penitrem A or a combination of propranolol, phentolamine, atropine (all 1 microM) and capsaicin (10 microM) in myometrial strips from nonpregnant rats. These results indicate that whereas BK(Ca) channels play little or no part in controlling basal rhythmicity in rat myometrium, K(V) channels appear to play a crucial role in this regard, especially during mid- and late pregnancy.