Anxiety in Turner syndrome: Engaging community to address barriers and facilitators to diagnosis and care

Turner syndrome (TS), caused by complete or partial loss of the second sex chromosome, is associated with complex medical manifestations. The TS community identifies anxiety as a major contributor to reduced quality of life. The study aimed to improve understanding of anxiety symptomatology, diagnosis, and care in individuals with TS. A mixed methods design integrated community engagement, including community leaders as co-investigators and a community advisory board, an online survey (N = 135), and in-depth interviews (N = 10). The majority of respondents reported that anxiety symptoms occur two or more days per week, with self-advocates reporting more frequent symptoms than caregivers (p = 0.03). Self-advocates reported feeling anxious more often at school/work; both rater groups reported anxiety-related behaviors were most likely to be expressed at home. Insomnia was the most common symptom of anxiety endorsed across age and rater groups (>70%). Anxiety symptoms and triggers changed with age and often were undiagnosed or untreated during childhood. Therapy and medication were reported as helpful by most respondents who had tried these strategies. Qualitative themes included: 'Triggers for anxiety are related to TS', 'Anxiety impacts the whole family', and 'Opportunities for early identification and intervention'.

Inspiring New Science to Guide Healthcare in Turner Syndrome: Rationale, design, and methods for the InsighTS Registry

Inspiring New Science to Guide Healthcare in Turner Syndrome (InsighTS) Registry is a national, multicenter registry for individuals with Turner syndrome (TS) designed to collect and store validated longitudinal clinical data from a diverse cohort of patients with TS. Herein, we describe the rationale, design, and approach used to develop the InsighTS registry, as well as the demographics of the initial participants to illustrate the registry's diversity and future utility. Multiple stakeholder groups have been involved from project conceptualization through dissemination, ensuring the registry serves the priorities of the TS community. Key features of InsighTS include recruitment strategies to facilitate enrollment of participants that appropriately reflect the population of individuals with TS receiving care in the US, clarity of data ownership and sharing, and sustainability of this resource. The registry gathers clinical data on diagnosis, treatment, comorbidities, health care utilization, clinical practices, and quality of life with the goal of improving health outcomes for this population. Future directions include multiple patient-centered clinical-translational research projects that will use the InsighTS platform. This thorough and thoughtful planning will ensure InsighTS is a valuable and sustainable resource for the TS community for decades to come.

Information needs and health status in adolescents and young adults with differences of sex development or sex chromosome aneuploidies

INTRODUCTION

When and how to provide condition-related information to adolescents and young adults (AYAs) with differences of sex development or sex chromosome aneuploidies (DSDs or SCAs) is largely based on anecdotal experience and lacks informed guidance. For AYAs with a DSD or SCA, having accurate information is critical for attaining optimal adjustment and well-being, participating in decision making related to treatment options, and transitioning successfully to adult health care, yet prior studies have focused exclusively on parental perspectives and not on the views of adolescents themselves.

OBJECTIVE

The objective of this study was to describe unmet information needs in AYAs with a DSD or SCA and examine associations with perceived global health.

METHODS

Participants were recruited from specialty clinics at Children's Hospital of Philadelphia (n = 20) and Children's Hospital Colorado (n = 60). AYAs ages 12-21 years with a DSD or SCA and a parent completed a survey assessing perceived information needs across 20 topics, importance of those topics, and global health using the PROMIS Pediatric Global Health questionnaire (PGH-7).

RESULTS

AYAs had diagnoses of Klinefelter syndrome (41%), Turner syndrome (25%), and DSD (26%) and were 16.7 years (SD = 2.56) and 44% female. Parent participants were primarily mothers (81%). AYAs perceived that 48.09% of their information needs were unmet (SD = 25.18, range: 0-100). Parents perceived that 55.31% of AYAs' information needs were unmet (SD = 27.46 range: 5-100). AYAs and parents across conditions reported unmet needs related to information about transition to adult health care, financial support for medical care, and how the condition might affect the AYA's health in the future. While AYA-reported PGH-7 scores were not associated with percentage of AYA unmet information needs, parent-reported PGH-7 scores were (r = -.46, p < .001), such that lower parent-reported global health was associated with higher percentage of AYA unmet information needs.

DISCUSSION/CONCLUSION

On average, parents and AYAs perceived that half of AYAs' information needs were unmet, and a higher percentage of AYA unmet information needs was associated with lower perceived global health. The frequency of unmet needs in this sample of AYAs reflects an opportunity for improvement in clinical care. Future research is needed to understand how education to children and AYAs unfolds as they mature and to develop strategies to address the information needs of AYAs with a DSD or SCA, promote well-being, and facilitate AYA engagement in their own health care.

Epidemiology of Hepatitis E in 2017 in Bavaria, Germany

In the last decade, the number of reported hepatitis E virus (HEV) infections in Germany, including Bavaria, has continued to rise. In order to identify risk factors associated with HEV infection, we investigated notified hepatitis E cases from Bavaria during 2017. The project "Intensified Hepatitis E Surveillance in Bavaria" included interviews with questionnaires, collection and genotyping of stool, serum and food samples. In addition, certain risk factors were examined in a sample comparison with healthy population using univariable analysis and logistic regression. In total, 135 hepatitis E cases from Bavaria were included in the analysis. Mean age for women was 46 (range 20-74) years and 47.5 (range 20-85) for men. 56 of the cases (41.5%) were asymptomatic. Among the symptomatic cases, both men and women were equally affected with symptoms like fever (16.3%), jaundice (18.8%) and upper abdominal pain (28.2%). 145 human samples (serum, stool) and 6 food samples were collected. 15.9% of the human samples (n = 23) were positive for HEV RNA by reverse-transcription quantitative real-time PCR (RT-qPCR). Identified risk factors significantly associated with hepatitis E were sausage consumption with odds ratio 9.6 (CI 1.3-70.1), fish with OR 2.2 (CI 1.1-4.4) and cat ownership with OR 1.9 (CI 1.3-3.0) in multivariable analyses. Further investigation is needed to confirm the role of fish in HEV transmission. Autochthonous HEV genotype 3 is prevalent in Bavaria and there could be more transmission routes contributing to the spread of HEV than previously known. Undercooked meat, offal, sausages, fish, shellfish and contact with animals and pets are possible sources for infection.

Differences in Patient and Parent Informant Reports of Depression and Anxiety Symptoms in a Clinical Sample of Transgender and Gender Diverse Youth

Purpose: We assessed characteristics of patients at a pediatric gender clinic and investigated if reports of mental health concerns provided by transgender and gender diverse (TGD) youth patients differed from reports provided by a parent informant on their behalf. Methods: This cross-sectional study included 259 TGD patients 8 to 22 years of age attending a pediatric gender clinic in the southeast United States from 2015 to 2020. Pearson correlations and paired sample t-tests compared patient-reported mental health concerns at patient intake with those provided by a parent informant. Clinical symptom severity was assessed with standardized T-scores. Level 2 Patient-Reported Outcomes Measurement Information System (PROMIS) Emotional Distress-Depression Scale and Level 2 PROMIS Emotional Distress-Anxiety Scale assessed depression and anxiety symptoms of patients. Diagnostic and Statistical Manual of Mental Disorders Fifth Edition Parent/Guardian-Rated Level 1 Cross-Cutting Symptom Measure was used with parents. Results: Patients had a mean age of 14.9 at first visit, with most identifying as White (85.5%), non-Hispanic (91.1%), and as a boy or man (63.6%). Half had moderate-to-severe depression (51.2%) or anxiety (47.9%) symptoms. There was a moderate, positive correlation between patient-reported and parent-reported depression symptoms, with no correlation for anxiety symptoms. Informant type differences were statistically significant (patients reporting greater depression and anxiety symptoms). Conclusions: TGD youth patients reported more severe depression and anxiety symptoms compared with parent informants. Despite moderate agreement on depression symptoms, parents did not accurately detect their child's anxiety symptoms. These discrepancies highlight a need for interventions which increase parental recognition of child mental health status.

Congenital renal anomalies in cloacal exstrophy: Is there a difference?

INTRODUCTION

Cloacal exstrophy (CE) is the most severe manifestation of the epispadias-exstrophy spectrum. Previous studies have indicated an increased rate of renal anomalies in children with classic bladder exstrophy (CBE). Given the increased severity of the CE defect, it was hypothesized that there would be an even greater incidence among these children.

OBJECTIVE

The primary objective was to characterize renal anatomy in CE patients. Two secondary objectives were to compare these renal anatomic findings in male and female patients, and female patients with and without Müllerian anomalies.

STUDY DESIGN

An Institutional Review Board-approved retrospective review of 75 patients from an institutional exstrophy database. Data points included: age at analysis, sex, and renal and Müllerian anatomy. Abnormal renal anatomy was defined as a solitary kidney, malrotation, renal ectopia, congenital cysts, duplication, and/or proven obstruction. Abnormal Müllerian anatomy was defined as uterine or vaginal duplication, obstruction, and/or absence.

RESULTS

The Summary Table presents demographic data and renal anomalies. Males were more likely to have renal anomalies. Müllerian anomalies were present in 65.7% of female patients. Girls with abnormal Müllerian anatomy were 10 times more likely to have renal anomalies than those with normal Müllerian anatomy (95% CI 1.1-91.4, P = 0.027).

DISCUSSION

Patients with CE had a much higher rate of renal anomalies than that reported for CBE. Males and females with Müllerian anomalies were at greater risk than females with normal uterine structures. Mesonephric and Müllerian duct interaction is required for uterine structures to develop normally. It has been proposed that women with both Müllerian and renal anomalies be classified separately from other uterine malformations on an embryonic basis. In these patients, an absent or dysfunctional mesonephric duct has been implicated as potentially causal. This provided an embryonic explanation for uterine anomalies in female CE patients. There were also clinical implications. Women with renal agenesis and uterine anomalies were more likely to have endometriosis than those with isolated uterine anomalies, but were also more likely to have successful pregnancies. Males may have had an analogous condition with renal agenesis and seminal vesicle cysts. Future research into long-term kidney function in this population, uterine function, and possible male sexual duct malformation is warranted.

CONCLUSION

Congenital renal anomalies occurred frequently in children with CE. They were more common in boys than in girls. Girls with abnormal Müllerian anatomy were more likely to have anomalous renal development. Mesonephric duct dysfunction may be embyologically responsible for both renal and Müllerian maldevelopment.

Roles of mitochondria and temperature in the control of intracellular calcium in adult rat sensory neurons

We recorded Ca2+ current and intracellular Ca2+ ([Ca2+](i)) in isolated adult rat dorsal root ganglion (DRG) neurons at 20 and 30 degrees C. In neurons bathed in tetraethylammonium and dialyzed with cesium, warming reduced resting [Ca2+](i) from 87 to 49 nM and the time constant of the decay of [Ca2+](i) transients (tau(r)) from 1.3 to 0.99s (Q(10)=1.4). The Buffer Index, the ratio between Ca2+ influx and Delta[Ca2+](i) (f I(ca)d(t)/Delta[Ca2+]i) , increased two- to threefold with warming. Neither inhibition of the plasma membrane Ca2+ -ATPase by intracellular sodium orthovanadate nor inhibition of Ca2+ uptake by the endoplasmic reticulum by thapsigargin plus ryanodine were necessary for the effects of warming on these parameters. In contrast, inhibition of the mitochondrial Ca2+ uniporter by intracellular ruthenium red largely reversed the effects of warming. Carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP, 500 nM) increased resting [Ca2+](i) at 30 degrees C. Ten millimolar intracellular sodium prolonged the recovery of [Ca2+](i) transients to 10-40s. This effect was reversed by an inhibitor of mitochondrial Na(+)/Ca2+ -exchange (CGP 37157, 10 microM). Thus, mitochondrial Ca2+ uptake is necessary for the temperature-dependent increase in Ca2+ buffering and mitochondrial Ca2+ fluxes contribute to the control of [Ca2+](i) between 50 and 150 nM at 30 degrees C.

Allele-specific quantification of HLA-DQB1 gene expression by real-time reverse transcriptase-polymerase chain reaction

In addition to coding region polymorphism, allele-specific variation in the upstream regulatory region of the HLA-DQB1 gene has been detected. Reporter gene assays and transfection studies have indicated that HLA-DQB1 promoter polymorphism may be of functional significance. The aim of this study was to utilize real-time reverse transcriptase-polymerase chain reaction (RT-PCR) for allele-specific quantification of HLA-DQB1 expression and to analyze cell-specific HLA-DQB1 expression in vivo. For the allele-specific quantification of DQB1 gene products, a real-time RT-PCR set of primer pairs (n=27) and probes (n=5) targeting exon 2 variability was established. The robustness and integrity of the assay system were confirmed by using recombinant DQB1 exon 2 plasmid clones as active exogenous controls. Sensitivity and reproducibility were assessed by serial dilution and allelic mixing analyses. In application to the study of allele-specific expression of DQB1 gene products during cytokine-driven maturation of monocyte-derived dendritic cells, differential patterns of allelic expression in heterozygous individuals were observed for DQB1*0301, compared to DQB1*0501 and DQB1*0602. At maximum, 1.9-fold (*0301/*0501) and 2.5-fold (*0301/*0602) higher induction was seen for DQB*0301. In conclusion, HLA-DQB1 expression can be analyzed by real-time RT-PCR suitable for cell- and allele-specific detection of HLA-DQB1 transcripts in homo- and heterozygous combinations.

Functional and molecular expression of a voltage-dependent K(+) channel (Kv1.1) in interstitial cells of Cajal

1. Located within the gastrointestinal (GI) musculature are networks of cells known as interstitial cells of Cajal (ICC). ICC are associated with several functions including pacemaker activity that generates electrical slow waves and neurotransmission regulating GI motility. In this study we identified a voltage-dependent K(+) channel (Kv1.1) expressed in ICC and neurons but not in smooth muscle cells. 2. Transcriptional analyses demonstrated that Kv1.1 was expressed in whole tissue but not in isolated smooth muscle cells. Immunohistochemical co-localization of Kv1.1 with c-kit (a specific marker for ICC) and vimentin (a specific marker of neurons and ICC) indicated that Kv1.1-like immunoreactivity (Kv1.1-LI) was present in ICC and neurons of GI tissues of the dog, guinea-pig and mouse. Kv1.1-LI was not observed in smooth muscle cells of the circular and longitudinal muscle layers. 3. Kv1.1 was cloned from a canine colonic cDNA library and expressed in Xenopus oocytes. Pharmacological investigation of the electrophysiological properties of Kv1.1 demonstrated that the mamba snake toxin dendrotoxin-K (DTX-K) blocked the Kv1.1 outward current when expressed as a homotetrameric complex (EC(50) = 0.34 nM). Other Kv channels were insensitive to DTX-K. When Kv1.1 was expressed as a heterotetrameric complex with Kv1.5, block by DTX-K dominated, indicating that one or more subunits of Kv1.1 rendered the heterotetrameric channel sensitive to DTX-K. 4. In patch-clamp experiments on cultured murine fundus ICC, DTX-K blocked a component of the delayed rectifier outward current. The remaining, DTX-insensitive current (i.e. current in the presence of 10(-8) M DTX-K) was outwardly rectifying, rapidly activating, non-inactivating during 500 ms step depolarizations, and could be blocked by both tetraethylammonium (TEA) and 4-aminopyridine (4-AP). 5. In conclusion, Kv1.1 is expressed by ICC of several species. DTX-K is a specific blocker of Kv1.1 and heterotetrameric channels containing Kv1.1. This information is useful as a means of identifying ICC and in studies of the role of delayed rectifier K(+) currents in ICC functions.

Alosetron and the rapid component of delayed rectifying potassium current in cardiac cells

Some drugs acting on 5-hydroxytryptamine receptors inhibit the rapid component of delayed rectifying potassium currents (I(Kr)) in cardiac muscle cells. This is associated with lengthening of the QT interval in the cardiac cycle and can lead to fatal arrhythmias. We investigated whether alosetron, a novel 5HT3 antagonist proposed for treatment of irritable bowel syndrome (IBS), blocks I(Kr) in guinea pig cardiac myocytes. I(Kr) was isolated under whole-cell voltage clamp, and was identified by its sensitivity to the selective I(Kr) antagonist E4031. Cisapride (10(-6) M) inhibited the E4031-sensitive current while alosetron (10(-10)-10(-6) M) had no effect on I(Kr). We also found that alosetron did not inhibit I(Ks). Therefore, use of alosetron for treatment of IBS should not be confounded by long QT syndrome.

Blocking of cloned and native delayed rectifier K channels from visceral smooth muscles by phencyclidine

We investigated the effect of phencyclidine (PCP) on three native delayed rectifier K+ currents and three channels cloned from canine and human circular colonic myocytes using voltage-clamp techniques. Native delayed rectifier K+ current in canine circular colon is composed of at least three components: (i) a rapidly activating, 4-aminopyridine-sensitive component (termed IdK(f)); (ii) a slowly activating, tetraethylammonium (TEA)-sensitive component (IdK(s)); and (iii) a rapidly activating, TEA-sensitive component, which has a steady-state inactivation curve shifted towards more negative potentials (IdK(n)). PCP blocked all three components with EC50 values of 45, 27 and 59 micromol L-1, respectively. Blocking was neither use-dependent nor voltage-dependent. Delayed rectifier K+ channels cloned from canine (Kv1.2, Kv1.5) and from human (Kv2.2) colon were expressed in Xenopus oocytes. PCP blocked all three currents with similar potency. In contrast, PCP (up to 10-4 mol L-1) did not reduce the magnitude of Ca2+-dependent outward current of large conductance Ca2+-activated K+ channels (BK channels).

Extragenic pleiotropic mutations that repress glycosyl hydrolase expression in the hyperthermophilic archaeon Sulfolobus solfataricus

The hyperthermophilic archaeon Sulfolobus solfataricus employs a catabolite repression-like regulatory system to control enzymes involved in carbon and energy metabolism. To better understand the basis of this system, spontaneous glycosyl hydrolase mutants were isolated using a genetic screen for mutations, which reduced expression of the lacS gene. The specific activities of three glycosyl hydrolases, including an alpha-glucosidase (malA), a beta-glycosidase (lacS), and the major secreted alpha-amylase, were measured in the mutant strains using enzyme activity assays, Western blot analysis, and Northern blot analysis. On the basis of these results the mutants were divided into two classes. Group I mutants exhibited a pleiotropic defect in glycosyl hydrolase expression, while a single group II mutant was altered only in lacS expression. PCR, Southern blot analysis, comparative heterologous expression in Escherichia coli, and DNA sequence analysis excluded cis-acting mutations as the explanation for reduced lacS expression in group I mutants. In contrast lacS and flanking sequences were deleted in the group II mutant. Revertants were isolated from group I mutants using a lacS-specific screen and selection. These revertants were pleiotropic and restored glycosyl hydrolase activity either partially or completely to wild-type levels as indicated by enzyme assays and Western blots. The lacS mutation in the group II mutant, however, was nonrevertible. The existence of group I mutants and their revertants reveals the presence of a trans-acting transcriptional regulatory system for glycosyl hydrolase expression.

Coordinate transcriptional control in the hyperthermophilic archaeon Sulfolobus solfataricus

The existence of a global gene regulatory system in the hyperthermophilic archaeon Sulfolobus solfataricus is described. The system is responsive to carbon source quality and acts at the level of transcription to coordinate synthesis of three physically unlinked glycosyl hydrolases implicated in carbohydrate utilization. The specific activities of three enzymes, an alpha-glucosidase (malA), a beta-glycosidase (lacS), and an alpha-amylase, were reduced 4-, 20-, and 10-fold, respectively, in response to the addition of supplementary carbon sources to a minimal sucrose medium. Western blot analysis using anti-alpha-glucosidase and anti-beta-glycosidase antibodies indicated that reduced enzyme activities resulted exclusively from decreased enzyme levels. Northern blot analysis of malA and lacS mRNAs revealed that changes in enzyme abundance arose primarily from reductions in transcript concentrations. Culture conditions precipitating rapid changes in lacS gene expression were established to determine the response time of the regulatory system in vivo. Full induction occurred within a single generation whereas full repression occurred more slowly, requiring nearly 38 generations. Since lacS mRNA abundance changed much more rapidly in response to a nutrient down shift than to a nutrient up shift, transcript synthesis rather than degradation likely plays a role in the regulatory response.

Charybdotoxin block of Ca(2+)-activated K+ channels in colonic muscle depends on membrane potential dynamics

Charybdotoxin (ChTX) is a specific blocker of Ca(2+)-activated K+ channels. The voltage- and time-dependent dynamics of ChTX block were investigated using canine colonic myocytes and the whole cell patch-clamp technique with step and ramp depolarization protocols. During prolonged step depolarizations, K+ current slowly increased in the continued presence of ChTX (100 nM). The rate of increase depended on membrane potential with an e-fold change for every 60 mV. During ramp depolarizations, the effectiveness of ChTX block depended significantly on the rate of the ramp (50% at 0.01 V/s to 80% at 0.5 V/s). Results are consistent with a mechanism in which ChTX slowly "unbinds" in a voltage-dependent manner. A simple kinetic model was developed in which ChTX binds to both open and closed states. Slow unbinding is consistent with ChTX having little effect on electrical slow waves recorded from circular muscle while causing depolarization and contraction of longitudinal muscle, which displays more rapid "spikes." Resting membrane potential and membrane potential dynamics are important determinants of ChTX action.

Determination of channel open probabilities from multichannel data

We developed a method for determining whether channels in a multichannel patch or bilayer have the same or statistically significantly different open probabilities. We use a maximum likelihood method to fit the distribution of (unbinned) current amplitudes and to provide estimates of individual channel open probabilities, single channel currents, and standard deviations of the channel currents. These parameters are used to compare models with increasing constraints on the open probabilities including the model where all channels have different open probabilities and the model where all channels have the same open probability. A chi 2 statistic is used to identify models that are statistically less likely to predict the data. The ability of multichannel data to determine individual open probabilities is limited by two factors: the signal to noise ratio of the record and the fact that changes in amplitude distributions caused by a 0.2 difference in open probabilities are comparable in magnitude to the variations caused by random channel gating. These limitations notwithstanding, we demonstrate the utility of our approach by using it to analyze the open probabilities of 3 large conductance Ca2(+)-activated K+ channels in an artificial lipid bilayer revealing the response of one of those channels to GTP gamma S.

Regulation of ion channels in smooth muscles by calcium

Intracellular Ca2+ concentration ([Ca2+]i) plays a central role in regulating tone and contractility of smooth muscle cells. In contrast to the "classic" model of electromechanical coupling where membrane potential determines [Ca2+]i, it is now well established that [Ca2+]i in turn may also affect membrane potential by modulating open probabilities of ion channels. Activation by [Ca2+]i of large-conductance K+ channels, Cl- channels, and nonselective cation channels has been described, as well as block of delayed rectifier K+ channels by [Ca2+]i and [Ca2+]i-induced inactivation of Ca2+ channels. Therefore, a network consisting of positive- and negative-feedback loops regulates [Ca2+]i as well as membrane potential. In this context, we review the properties of Ca(2+)-dependent ion channels and their functional role in vascular and visceral smooth muscles. Any alteration of the "Ca2+ sensitivity" of ion channels is expected to have a profound effect on the reciprocal relationship between membrane potential and [Ca2+]i. Already several molecular factors determining Ca2+ sensitivity of Ca(2+)-activated K+ channels have been identified. We provide a working definition for Ca2+ sensitivity.

Regulation of smooth muscle delayed rectifier K+ channels by protein kinase A

We identified voltage-activated K+ channels in freshly dispersed smooth muscle cells from the circular layer of the canine colon in patch-clamp experiments using 200 nM charybdotoxin to suppress 270-pS Ca2+-activated K+ channels (BK channels). Three channel types were distinguished in symmetrical 140 mM KCl solutions: 19.5 +/- 1.7 pS channels (KDR1), 90.6 +/- 5.4 pS channels (KDR2) and 149 +/- 4 pS intermediate-conductance Ca2+-activated K+ channels (IK channels). All three types showed an increase in open probability with membrane depolarization. Ensemble average current from KDR1 channels inactivated with a time constant of 1.7 +/- 0.1 s at +60 mV test potential, while KDR2 and IK channels did not show inactivation. IK channels were activated by free cytoplasmic [Ca2+] (10(-6 )M) but were insensitive to 4-aminopyridine (4-AP, 10 mM) and intracellular tetraethylammonium (TEA, 1 mM). KDR1 channels were sensitive to 4-AP (10 mM) and intracellular TEA (1-10 mM) but not to Ca2+. KDR2 channels did not have a consistent pharmacological profile, suggesting that this class may be comprised of several subtypes. At +40 mV membrane potential, the catalytic subunit of protein kinase A (PKA) increased the open probability of KDR1 channels 3.4-fold and of KDR2 channels 3.9-fold, but had no effect on IK channels. In the absence of Mg-ATP, PKA did not affect channel open probabilities. At physiological membrane potentials (-60 mV) only openings of KDR1 channels could be induced by PKA, suggesting that these 4-AP-sensitive 20-pS K+ channels are primarily responsible for the cAMP-mediated hyperpolarization of colonic smooth muscle cells.

Nitric oxide activates multiple potassium channels in canine colonic smooth muscle

1. Nitric oxide (NO), an inhibitory neurotransmitter released from peripheral neurones, hyperpolarizes smooth muscle cells and inhibits contraction. The mechanism of this hyperpolarization is unknown. 2. We have identified three classes of K+ channels activated by NO and NO donors in colonic smooth muscle cells. NO and NO donors increased the open probability of 80 pS channels (KNO1), very small channels (< 4 pS, KNO2), and 270 pS Ca(2+)-activated K+ channels (BK channels) in cell-attached patches. 3. Dibutyryl cGMP and 8-bromo cGMP also increased the open probability of KNO1 and KNO2 in cell-attached patches. 4. In excised patches of membrane, direct application of NO or the NO donor, S-nitroso-N-acetyl penicillamine (SNAP), increased the open probability of KNO1 and KNO2, but cGMP or dibutyryl cGMP had no effect. SNAP had no effect on the open probability of BK channels in excised patches. 5. The reducing agent dithiothreitol and the alkylating agent N-ethylmaleimide blocked NO-induced channel openings. 6. In summary, the hyperpolarization response to NO in smooth muscles may be mediated by multiple K+ channels. At least two of these classes of channels may be activated by dual pathways involving direct activation by NO and cGMP-mediated mechanisms.

Posterior cervical spine fusion with tension-band wiring

In this study the authors detail their experience with posterior tension-band wiring for stabilization of the subaxial cervical spine. Fifty-five patients underwent fusion for trauma (41 patients), degenerative disease (13 patients), and tumor (one patient). The fusion rate was 96% (50 of 52 patients) and postoperative immobilization was accomplished by means of a Philadelphia collar in the majority of cases. Tension-band wiring provides a stable construct that is simple to perform, requires fusion of a minium number of motion segments, and allows early mobilization with only a hard collar needed for support. The details of the technique, which has been modified from preliminary descriptions, are discussed.

Multiple components of delayed rectifier K+ current in canine colonic smooth muscle

1. We investigated the pharmacology and voltage-dependent activation and inactivation kinetics of the 'delayed rectifier' K+ current, IdK, in canine colonic myocytes and developed protocols which separate this current into three distinct components that differ in their kinetics and pharmacology. 2. Block of IdK by TEA or 4-aminopyridine (4-AP) alone was incomplete. Maximal concentrations of TEA or 4-AP blocked 76% (EC50 = 2.6 mM) and 51% (EC50 = 69 mM) of current, respectively. In the presence of 10 mM 4-AP, IdK could be blocked completely by TEA. 3. TEA and 4-AP had distinct effects on current activation: time constants for activation of IdK at +10 mV were 25.6 +/- 4.4 ms under control conditions, 40.3 +/- 7.6 ms in the presence of 10 mM 4-AP and 16.7 +/- 2.3 ms with 10 mM TEA in the bath solution. 4-AP block and removal of block were use dependent, but no frequency dependence or voltage dependence of steady-state block could be detected. These data are consistent with the presence of a rapidly activating 4-AP-sensitive current, IdK(f), and a more slowly activating TEA-sensitive current component, IdK(s). 4. A third component of the delayed rectifier current, IdK(n), was revealed when 10 mM TEA was included in the pipette solution. IdK(n) was rapidly activating, had a membrane potential at half-maximal inactivation (V1/2) for steady-state inactivation 13 mV negative of that for the mixed IdK, was completely insensitive to 4-AP (10 mM) and was blocked by external TEA with an EC50 of 7.7 mM. 5. These data demonstrate that the delayed rectifier current in canine colonic smooth muscle is composed of three currents, IdK(f), IdK(s) and IdK(n). All three currents are insensitive to charybdotoxin (100 nM).

Role of Ca(2+)-activated K+ channels in electrical activity of longitudinal and circular muscle layers of canine colon

The role of Ca(2+)-activated K+ channels (BK channels) in the canine colon was evaluated by testing the effects of charybdotoxin (ChTX) and tetraethylammonium on K+ currents of isolated myocytes and on electrical and mechanical activity of tissue strips. ChTX blocked Ca(2+)-activated outward current [IK(Ca)] in a dose- and voltage-dependent manner. No significant differences in IK(Ca) density, ChTX block, or Ca2+ sensitivity of BK channels were observed between circular and longitudinal myocytes. ChTX (100 nM) blocked 60% of current at +80 mV. Delayed rectifier current was not inhibited by 100 nM ChTX. In the absence of agonists, ChTX did not affect electrical or mechanical activity of circular muscle strips. In the presence of 10(-6) M BAY K 8644 or 10(-6) M acetylcholine, ChTX increased slow-wave duration and amplitude, induced membrane potential oscillations, and potentiated contraction. In unstimulated longitudinal muscle strips, ChTX depolarized the tissue, increased burst duration and spiking frequency, and resulted in an increase in contractions. These results indicate that BK channels are important regulators of colonic motility. In the longitudinal layer, BK channels are involved in setting membrane potential and determine excitability. In the circular layer, ChTX-sensitive channels do not participate in the in vitro basal electrical activity but limit the responses to excitatory agonists.

Block by 4-aminopyridine of a Kv1.2 delayed rectifier K+ current expressed in Xenopus oocytes

1. The blocking action of 4-aminopyridine (4-AP) on a delayed rectifier Kv1.2 K+ channel expressed in oocytes was investigated at room temperature (22 degrees C) and physiological temperature (34 degrees C) using the double-electrode voltage clamp and patch clamp techniques. 2. At room temperature, 4-AP (100 microM) inhibition occurred only after activation of current. The rate of onset of block was dependent upon the length of time current was activated by a depolarizing step. Similarly, removal of block required current activation. The degree of steady-state block by 4-AP was not reduced by increasingly more depolarized step potentials. The degree of steady-state block also did not change over the duration of a 1 s step. 3. When channels were nearly fully inactivated, 4-AP produced no additional block of a subsequent depolarizing step, suggesting that 4-AP did not bind when channels were in the inactivated state. In single channel experiments, 4-AP decreased the mean open time in a dose-dependent manner but did not alter the single-channel current amplitude. 4. At 34 degrees C the I-V relationship and inactivation curve shifted to more negative potentials. Increasing the temperature to 34 degrees C did not alter the degree of block by 4-AP, although the rate of onset of block was greatly enhanced. 5. Results suggest that 4-AP binds to the open state of the Kv1.2 channel and is trapped when the channel closes. 4-AP cannot bind when the channel is closed or inactivated prior to the addition of the drug. C-type inactivation and 4-AP binding to the channel are mutually exclusive. A model for the proposed mechanism of action of 4-AP on the Kv1.2 channel is proposed based on experimental data.

Cloning and characterization of a Kv1.5 delayed rectifier K+ channel from vascular and visceral smooth muscles

We have cloned and characterized the expression of a Kv1.5 K+ channel (cKv1.5) from canine colonic smooth muscle. The amino acid sequence displayed a high level of identity to other K+ channels of the Kv1.5 class in the core region between transmembrane segments S1-S6; however, identity decreased to between 74 and 82% in the NH2 and COOH terminal segments, suggesting that cKv1.5 is a distinct isoform of the Kv1.5 class. Functional expression of cKv1.5 in oocytes demonstrated a channel highly selective for K+, which activates in a voltage-dependent manner on depolarization to membrane potentials positive to -40 mV. At room temperature the channel showed fast activation (time to half of peak current, 5.5 ms) and slow inactivation that was incomplete after 20-s depolarizations. Single channel analysis of the channel expressed in oocytes displayed a linear current-voltage curve and had a slope conductance of 9.8 +/- 1.1 pS. Northern blot analysis demonstrated differential expression of cKv1.5 in smooth muscles of the gastrointestinal tract and abundant expression in several vascular smooth muscles. We propose that cKv1.5 represents a component of the delayed rectifier current in both vascular and visceral smooth muscles.

Comparison of large-conductance Ca(2+)-activated K+ channels in artificial bilayer and patch-clamp experiments

We compared the gating, ion conduction, and pharmacology of large-conductance Ca(2+)-activated K+ channels (BK channels) from canine colon in artificial lipid bilayers and in excised patches. Both protocols identified 270-pS K(+)-selective channels activated by depolarization and Ca2+ (approximately 130-mV shift of half-activation voltage per 10-fold change in Ca2+) that were inhibited by extracellular tetraethylammonium (TEA) and charybdotoxin. These similarities suggest that the same BK channels are studied in the two techniques. However, we found three quantitative differences between channels in artificial bilayers and patches. 1) Channels in artificial bilayers required fivefold higher free Ca2+ or 80-mV stronger depolarization for activation. 2) The voltage dependence of TEA block was smaller for channels in artificial bilayers. The apparent distance across the membrane field for the TEA binding site was 0.031 for channels in artificial bilayers and 0.23 for channels in patches. 3) ATP (2 mM) decreased open probability (Po) of channels in artificial bilayers, whereas channels in patches were unaffected. Neither GTP nor UTP reduced Po of channels in artificial bilayers. It is possible that these differences may be due to a lack of molecular identity between the channels studied in the two protocols. Alternatively, they may be attributed to alterations in channel properties during reconstitution or to influences of the artificial lipid environment.

Mechanism of cyclic AMP-induced hyperpolarization in canine colon

The mechanism of forskolin (FSK)-induced hyperpolarization was investigated in strips of canine colonic circular muscle. FSK responses were compared to those of the K+ channel opener lemakalim (LEM). Both FSK (10 microM) and LEM (10 microM) hyperpolarized cells near the myenteric border by 10 to 20 mV. Responses to both agents were abolished by 35 mM external K+, indicating a probable mediation by K+ channels. FSK increased the open probability of Ca(++)-activated K+ channels in isolated colonic myocytes. However, in muscle strips charybdotoxin (100 nM) and tetraethylammonium (10 mM) failed to reduce FSK- and LEM-induced hyperpolarizations whereas tetrapentylammonium (50 microM) and 4-aminopyridine (10 mM) blocked both responses. Phencyclidine (100 microM), Ba++ (1 mM) and the antagonist of ATP-sensitive K+ currents glybenclamide (10 microM) blocked LEM- but not FSK-induced hyperpolarizations. Delayed rectifier current in isolated myocytes was activated near -20 mV and was blocked by (order of potency): nifedipine > tetrapentylammonium > phencyclidine > 4-aminopyridine > tetraethylammonium. Charybdotoxin (100 nM), Ba++ (1 mM) and glybenclamide (10 microM) were without effect. Ca(++)-activated K+ current was activated near +30 mV and was blocked by: charybdotoxin > tetraethylammonium > tetrapentylammonium >> phencyclidine = 4-amino-pyridine. These data suggest that LEM induces membrane hyperpolarization by activation of a K+ current with a pharmacology similar to ATP-sensitive K+ current whereas cyclic AMP-induced hyperpolarization appears to involve activation of a current other than delayed rectifier current, Ca(++)-activated K+ current or ATP-sensitive K+ current.

Cloning and expression of a Kv1.2 class delayed rectifier K+ channel from canine colonic smooth muscle

A cDNA (CSMK1) encoding a delayed rectifier K+ channel of the Kv1.2 class was cloned from canine colonic circular smooth muscle and expressed in Xenopus oocytes. These channels appear to be uniquely expressed in gastrointestinal muscles and may participate in the electrical slow wave activity. Functional expression of CSMK1 in Xenopus oocytes demonstrated a K+ current that activated in a voltage-dependent manner upon depolarization. This current was highly sensitive to 4-aminopyridine (IC50, 74 microM). A low-conductance K+ channel was identified in inside-out patches from oocytes injected with CSMK1. This channel displayed a linear current-voltage relation with a slope conductance of 14 pS. The channels were blocked in a concentration-dependent manner by 4-aminopyridine. Northern blot analysis demonstrated that CSMK1 is expressed in a wide variety of gastrointestinal smooth muscles. Portal vein, renal artery, and uterus do not express CSMK1, suggesting that, among smooth muscles, expression of this K+ channel may be restricted to gastrointestinal smooth muscles. CSMK1 is 91% homologous to RAK, a delayed rectifier K+ channel cloned from rat heart, but displays unique pharmacological properties and tissue distribution.

Burst fractures of the fifth lumbar vertebra

Eleven patients with burst fractures of the fifth lumbar vertebra were reviewed. The results of nonoperative treatment were compared with that of immediate surgery and stabilization with pedicle screw fixation. Five patients were treated nonoperatively and six patients underwent pedicle screw instrumentation and spinal fusion. Five patients had neurologic injury associated with their L5 burst fracture. Nonoperative treatment yielded excellent results in young patients with minimal canal compromise. Neurologic deficits responded more predictably to surgical decompression than to conservative treatment and internal fixation with pedicle screws restores spinal stability and allows early mobilization.

S-nitrosocysteine, but not sodium nitroprusside, produces apamin-sensitive hyperpolarization in rat gastric fundus

1. To investigate the pharmacological properties of the membrane hyperpolarization induced by electrical field stimulation (EFS), sodium nitroprusside (SNP) and S-nitrosocysteine (NO-Cys) in circular smooth muscle cells of the rat gastric fundus (forestomach), the effects of various potassium channel blockers on these hyperpolarizations were investigated. 2. EFS (50 microseconds, 20 Hz, 3 pulses, 10-50 V) produced inhibitory junction potentials (i.j.ps), in the presence of atropine (1 microM) and guanethidine (1 microM). NO-Cys and SNP produced hyperpolarization of the membrane in the rat gastric fundus. L-NG-nitroarginine (L-NNA) inhibited the i.j.ps, but not the hyperpolarization induced by NO-Cys and SNP. This inhibitory action of L-NNA on the i.j.ps was partly reversed by subsequent application of L-arginine (1 mM) but not by D-arginine. 3. Oxyhaemoglobin (Oxy-Hb; 5 microM) inhibited these hyperpolarizations, although a higher concentration of Oxy-Hb was required to inhibit the SNP-induced hyperpolarization. Hydroquinone (50 microM) inhibited only the hyperpolarization induced by NO-Cys. 4. Apamin (1 microM) partly inhibited i.j.ps and NO-Cys-induced hyperpolarization, but not the SNP-induced hyperpolarization. Tetraethylammonium (TEA; 1 mM), 4-aminopyridine (4-AP; 1 mM) or glibenclamide (1 microM) did not affect hyperpolarization induced by NO-Cys and SNP. 5. 8-Bromo cyclic guanosine 3':5'-monophosphate (1 mM) also produced hyperpolarization. Apamin (1 microM), TEA (1 mM) and glibenclamide (5 microM) all failed to inhibit this hyperpolarization. 6. These results indicate that NO-Cys and EFS hyperpolarize the membrane by activating apaminsensitive and TEA-resistant K+ channels and favour the hypothesis that a NO-liberating substance may act as a neurotransmitter in non-adrenergic, non-cholinergic (NANC) neurones in the rat forestomach.Our results also suggest that increase in cyclic GMP may cause apamin-resistant hyperpolarization but the apamin-sensitive hyperpolarization is mediated by another mechanism.

Inhibition of slow-wave repolarization and Ca(2+)-activated K+ channels by quaternary ammonium ions

We studied the effects of the K+ channel blocker tetrapentylammonium (TPeA) on the electrical activity of intact circular smooth muscle from canine colon. TPeA (10 and 20 microM) increased slow-wave duration and "locked" the membrane potential around -30 mV plateau potential after several minutes of application, suggesting that K+ channels are essential for termination of colonic slow waves. Repolarization and normal slow-wave activity resumed after 20-30 min of washout. The patch-clamp technique was used to study the block of large-conductance Ca(2+)-activated K+ channels (BK channels) by TPeA and tetraethylammonium (TEA) in excised and cell-attached patches from isolated colonic smooth muscle cells. Channel block was characterized by a voltage-dependent dissociation constant [Kd(V)] for the binding of TEA and TPeA to a blocking site located a fraction of the distance across the membrane field (delta). The extracellular TEA binding site had a Kd(0) of 0.33 mM and a delta of 0.23. The extracellular TPeA binding site had a Kd(0) of 2.2 mM but showed significantly less voltage dependence (delta = 0.02). The intracellular binding site for TEA was of low affinity [Kd(0) = 76 mM]. Intracellular TPeA was the most potent blocker of BK channel current [Kd(0) = 11.7 microM]. The voltage dependence of block by intracellular TPeA (delta = -0.21) was not significantly different from that of intracellular TEA (delta = -0.3). Internal TPeA (10 microM) also blocked a 70-pS K+ channel and a 23-pS K+ channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Cromakalim and lemakalim activate Ca(2+)-dependent K+ channels in canine colon

The effects of cromakalim (BRL 34915) and its (-) optical isomer, lemakalim (BRL 38227) on the activity of 265-pS Ca(2+)-activated K+ channels (BK channels) were examined in cell-attached and inside-out patches from canine colonic myocytes. In cell-attached patches lemakalim increased the open probability (Po) of BK channels. Mean NPo, where N is the number of channels per patch, at +50 mV increased from 0.08 to 0.26 (20 microM lemakalim). In inside-out patches, cromakalim and lemakalim increased channel NPo rapidly and reversibly. This increase in NPo was due to a shift in half-maximal activation. Glyburide (20 microM) prevented the increase in NPo caused by lemakalim in cell-attached patches and reversed the increase in NPo in inside-out patches. Under conditions where Ca(2+)-activated K+ channels were maximally activated, lemakalim failed to increase current or induce a second type of K+ channel activity. When tetraethylammonium (200 microM) was added to the pipette solution to block the BK channel half maximally, lemakalim also failed to induce a second type of channel. Adenosine triphosphate (1 or 2 mM) applied to the inner surface of inside-out patches had no effect on Po of BK channels. Finally, the effects of lemakalim on ensemble average currents, constructed from multiple openings of BK channels in cell-attached patches was found to successfully mimic the effects of the drug on whole-cell membrane currents. We conclude that cromakalim and lemakalim activate BK channels in canine colonic cells. Whether this action participates in the membrane hyperpolarization and the decrease in frequency and duration of slow waves produced by these compounds in intact colonic muscles remains to be investigated.

Nitric oxide and nitrosocysteine mimic nonadrenergic, noncholinergic hyperpolarization in canine proximal colon

Previous evidence suggests that nonadrenergic, noncholinergic (NANC) inhibitory neurotransmission in visceral muscles may be mediated by nitric oxide (NO). We have demonstrated that NO and the NO carrier S-nitrosocysteine can mimic the hyperpolarization in colonic muscle caused by nerve stimulation. The finding that S-nitrosocysteine breaks down fast enough to cause inhibitory junction potential (IJP)-like hyperpolarizations suggests that NO could be stored as a nitrosothiol in secretory vesicles in nerve terminals. Oxyhemoglobin blocked hyperpolarization responses to NO and S-nitrosocysteine and NANC IJPs. These findings suggest that NO is a biologically active transmitter substance in NANC inhibitory neurotransmission. NO enhanced the open probability of Ca(2+)-activated K+ channels in isolated colonic muscle cells. These channels may mediate the hyperpolarization response to NANC neurotransmission in colonic muscles.

Regulation of Ca(2+)-activated K+ channels by protein kinase A and phosphatase inhibitors

Many proteins including ion channels are regulated by phosphorylation. We tested the effect of 10 U/ml catalytic subunit protein kinase A on 260-pS Ca(2+)-activated K+ channels in excised inside-out membrane patches from freshly dispersed smooth muscle cells of the canine proximal colon. At +50 mV with 10(-7) M Ca2+ and -50 mV with 10(-6) M Ca2+, open probability of the channels was increased to 270 +/- 48% of control (n = 12). This increase was due to a shift in voltage-dependent activation by 13.9 +/- 3.2 mV (n = 3) to more negative potentials. Protein kinase A in the absence of ATP had no effect on channel activity (n = 3). Regulation by phosphorylation must be accompanied by dephosphorylation. We tested the effect of two potent inhibitors of protein phosphatases, calyculin A and okadaic acid. Application of 10(-9) to 10(-6) M of each inhibitor in the presence of protein kinase A further increased open probability by up to 250%. Calyculin A appeared to be less effective in increasing open probability than okadaic acid, suggesting that the phosphatase involved is neither type 1, 2A, nor 2B. Calyculin A in the absence of protein kinase A was ineffective. These data suggest that endogenous phosphatases are found in excised membrane patches and that a balance between phosphorylation and dephosphorylation may provide an important control of colonic motility.

Bilateral sacroiliac joint fracture-dislocation: a case report

Bilateral sacroiliac joint fracture-dislocation of the sacrum with displacement is a rare injury. We found only four such injuries previously reported in the literature. Nonoperative management in this case led to complete functional return and acceptable alignment.

Participation of Ca2(+)-activated K+ channels in electrical activity of canine gastric smooth muscle

1. The hypothesis that Ca2(+)-activated K+ channels participate in the repolarization of electrical slow waves was tested in isolated cells and intact muscles of the canine gastric antrum. 2. Freshly dispersed cells from the gastric antrum liberally express large conductance channels that were characterized as Ca2(+)-activated K+ channels by several criteria. 3. Mean slope conductance of these channels in symmetrical 140 mM-KCl solutions was 265 +/- 25 pS and reversal potential was 1.3 +/- 3.3 mV. The reversal potential was shifted when K+ was partially replaced with Na+ in a manner consistent with the Nernst equation for the K+ gradient. 4. Open probability was studied in excised patches in solutions containing 10(-7)-10(-6) M-Ca2+ with holding potentials ranging from -100 to +100 mV. Resulting activation curves were fitted by Boltzmann functions. 5. Increasing [Ca2+] from 10(-7) to 10(-6) M shifted the half-maximal activation from +99 to 0 mV. These data suggest that Ca2(+)-activated K+ channels may be activated in the voltage range and [Ca2+]i occurring during the plateau phase of the slow wave. 6. In intact muscles loaded with the photolabile Ca2+ chelator, nitr-5, photo-activated release of Ca2+ during the slow wave cycle produced changes consistent with activation of Ca2(+)-dependent outward currents. 7. The data are consistent with the idea that Ca2+ build-up during electrical slow waves shifts the activation voltage of Ca2(+)-activated K+ channels into the range of the plateau potential. Activation of these channels yields outward current and repolarization. 8. Since the force of contractions depends on slow wave amplitude and duration, regulation of these channels may be important in controlling gastric motility.

Measurement of single channel open probability with voltage ramps

In patches from membranes containing many active channels it is difficult to measure the voltage dependence of activation. We have developed a technique using ramp potentials to measure activation rapidly over a wide range of potentials. If the rate of change of holding potential is small compared to the activation or deactivation time constant of the channels voltage ramps can be used to measure N*p(open), where N is the number of channels per patch and p(open) is the open probability of the single channel. This provides a continuous reading of N*p(open) and allows an efficient measurement of channel activation over large voltage ranges. The voltage dependent activation of 200 pS Ca2(+)-activated K channels in excised patches from freshly dispersed canine colonic and gastric myocytes studied with voltage ramps was in good agreement with data obtained and analyzed with conventional methods at selected stationary voltages. This method has been found to be useful for studies of patches containing large number of channels and may be applied to characterize the voltage dependent activation of channels in several other tissues.

Ca2+-activated K channels of canine colonic myocytes

K channels in enzymatically dispersed circular smooth muscle cells from the canine proximal colon were studied with the patch-clamp technique. The most prominent channel in cell-attached and excised, inside-out patches was a K channel, which had slope conductances of approximately 100 pS at a holding potential of 0 mV in a physiological K+ gradient and approximately 200 pS in symmetrical 140 mM K+ solutions. The relative permeabilities of the channel for monovalent cations were 1.0 K+:0.5 Rb+: less than 0.07 Li+:less than 0.07 Na+. The channels were activated by potential and intracellular Ca2+. At Ca2+ concentrations less than 10(-7) M, channel openings were rare except at very positive potentials. At Ca2+ concentrations between 10(-7) and 10(-6) M the probability of channel opening increased steeply, and the voltage for channel activation shifted to a negative potential range, which cells experience during electrical slow wave events in situ. The effect of Ca2+ on the open-state probability of single channels was mainly due to a decrease in mean close time. Channels were blocked by 1 mM tetraethylammonium applied to the outside of the patch but up to 10 mM tetraethylammonium applied to the inside of the patch, and 4-aminopyridine applied to either side did not block the channel. The data suggest that this channel mediates a current important in the termination of electrical slow waves, which are the primary excitable event in colonic circular muscles.

Muscarinic suppression of Ca2+-dependent K current in colonic smooth muscle

Acetylcholine (ACh) increases the amplitude and duration of colonic electrical slow waves. This suggests that ACh either increases an inward current or suppresses an outward current. The latter hypothesis was tested in whole cell voltage-clamp experiments performed on freshly dispersed smooth muscle cells from canine proximal colon. Addition of ACh (10(-5) M) to solutions bathing cells reduced time-dependent outward currents elicited by depolarizing test pulses in the range of -45 to +30 mV. Analysis of tail currents showed that ACh caused a 10- to 15-mV positive shift in voltage-dependent activation. When cells were pretreated with 10(-6) M nifedipine to abolish the Ca2+-dependent component of the outward current, the reduction of outward current by ACh was blocked. Single-channel experiments were performed to determine whether ACh had a direct effect on Ca2+-activated K channels. ACh, 10(-5) M, added to bath and pipette solutions caused a positive shift in voltage-dependent activation in on-cell experiments. This effect of ACh on Ca2+-activated K channels provides a mechanism for the effects of muscarinic, excitatory stimulation of circular muscle of the colon.

Spontaneous electrical activity of interstitial cells of Cajal isolated from canine proximal colon

Interstitial cells of Cajal (ICC) have been suggested as pacemaker cells in the gastrointestinal tract. A method was developed to isolate ICC from the slow-wave pacemaker region of the canine proximal colon. These cells were identified under phase-contrast microscopy, and their identity was verified by comparing their ultrastructure with the morphology of ICC in situ. Patch-clamp experiments demonstrated that these cells are excitable; voltage-dependent inward and outward currents were elicited by depolarization. Inward current transients were identified as calcium currents. A portion of the outward current appears to be due to Ca2+-activated K channels commonly expressed in these cells. ICC were also spontaneously active, generating electrical depolarizations similar in waveform to slow-wave events of intact colonic muscles. These findings are consistent with the hypothesis that ICC initiate rhythmicity in the colon.