Systematic Implementation of Effective Quality Assurance Processes for the Assessment of Radiation Target Volumes in Head and Neck Cancer.

PURPOSE: Significant heterogeneity exists in clinical quality assurance (QA) practices within radiation oncology departments, with most chart rounds lacking prospective peer-reviewed contour evaluation. This has the potential to significantly affect patient outcomes, particularly for head and neck cancers (HNC) given the large variance in target volume delineation. With this understanding, we incorporated a prospective systematic peer contour-review process into our workflow for all patients with HNC. This study aims to assess the effectiveness of implementing prospective peer review into practice for our National Cancer Institute Designated Cancer Center and to report factors associated with contour modifications. METHODS AND MATERIALS: Starting in November 2020, our department adopted a systematic QA process with real-time metrics, in which contours for all patients with HNC treated with radiation therapy were prospectively peer reviewed and graded. Contours were graded with green (unnecessary), yellow (minor), or red (major) colors based on the degree of peer-recommended modifications. Contours from November 2020 through September 2021 were included for analysis. RESULTS: Three hundred sixty contours were included. Contour grades were made up of 89.7% green, 8.9% yellow, and 1.4% red grades. Physicians with >12 months of clinical experience were less likely to have contour changes requested than those with <12 months (8.3% vs 40.9%; P < .001). Contour grades were significantly associated with physician case load, with physicians presenting more than the median number of 50 cases having significantly less modifications requested than those presenting <50 (6.7% vs 13.3%; P = .013). Physicians working with a resident or fellow were less likely to have contour changes requested than those without a trainee (5.2% vs 12.6%; P = .039). Frequency of major modification requests significantly decreased over time after adoption of prospective peer contour review, with no red grades occurring >6 months after adoption. CONCLUSIONS: This study highlights the importance of prospective peer contour-review implementation into systematic clinical QA processes for HNC. Physician experience proved to be the highest predictor of approved contours. A growth curve was demonstrated, with major modifications declining after prospective contour review implementation. Even within a high-volume academic practice with subspecialist attendings, >10% of patients had contour changes made as a direct result of prospective peer review.

Efficacy of incisional negative pressure therapy in preventing post-sternotomy wound complications.

BACKGROUND: Sternal wound infections represent a source of significant morbidity and mortality following median sternotomy. The use of incisional negative pressure wound therapy in prevention has yet to be elucidated. METHODS: A retrospective study was conducted before and after a universal wound care protocol was implemented including the prophylactic use of negative pressure wound therapy (NPWT). The primary endpoint was sternal infections within 90 days of the index operation. RESULTS: In the control period, there was a 3.0% rate of sternal infection within 90 days compared to 0.8% in the intervention period (p < 0.001). An odds ratio of 0.25 (95% confidence interval 0.11, 0.57; p < 0.001) in the intervention period as compared to the control period was demonstrated. CONCLUSIONS: The use of a standardized wound care protocol including the universal application of NPWT for patients undergoing cardiac surgery with median sternotomy was an independent predictor of decreased rates of sternal infection.

A feasibility study of perioperative vitamin D supplementation in patients undergoing colorectal cancer resection.

Background: Vitamin D supplementation improves colorectal cancer (CRC) survival outcomes in randomized trials. The aim of this study was to test the feasibility, safety and efficacy of vitamin D supplementation in the pre- and perioperative period in patients undergoing CRC surgery. Methods: Patients were given 3200IU oral cholecalciferol (D3) per day perioperatively. Serial serum 25-hydroxyvitamin (25OHD) was measured by liquid chromatography tandem mass spectrometry and compared to untreated CRC controls. 25OHD and C-reactive protein (CRP) levels were compared using adjusted generalized linear mixed-effects models. Results: A total of 122 patients underwent serial perioperative sampling, including 41 patients given high-dose perioperative supplementation. Supplementation was well-tolerated with no adverse or serious adverse events related to supplementation reported. Pre-operative supplementation increased 25OHD levels on the day of surgery (103.9 vs. 42.5 nmol/l, P = 8.2E-12). Supplementation increased 25OHD levels at all post-operative timepoints (P < 0.001) and attenuated the post-operative drop in 25OHD (46 vs. 24% drop, P = 3.0E-4). Rate of vitamin D peri-operative insufficiency was significantly less in those on supplementation (e.g., day 3-5, 14 vs. 84%, P = 1.41E-08), with multivariate modeling across all timepoints indicating a ∼59 nmol/l higher 25OHD compared to control patients (P = 3.7E-21). Post-operative CRP was lower in patients taking supplementation (e.g., day 3-5 timepoint; 129 vs. 81 mg/l, P = 0.04). Conclusion: High dose pre-operative vitamin D supplementation is associated with higher perioperative 25OHD levels, lower rates of vitamin D insufficiency and reduced early post-operative CRP. Alongside published evidence for a beneficial effect of vitamin D on CRC survival outcomes, these novel findings provide strong rationale for early initiation of vitamin D supplementation after a diagnosis of CRC.

Understanding Cancer Screening Intention Among Physically Active Adults Ages 18-49.

Ideal efforts for cancer prevention would include lifestyle modifications along with routine, age-eligible cancer screening. Employing an asset-based approach within vulnerable populations already engaging in at least one healthy behavior (i.e., physical activity) may be an ideal way to further reduce cancer risk across peer groups with low cancer screening rates. Guided by the theory of planned behavior (TPB), the aim of this study was to identify constructs associated with cancer screening intentions among young to middle aged adults for influencing educational and behavioral interventions designed to promote cancer prevention. A cross-sectional, web-based survey was utilized to assess attitudes, subjective norms, perceived behavioral control, and intention to screen for cancer among physically active adults aged 18-49 years. Descriptive and bivariate analyses were conducted to characterize the sample, and hierarchical linear regression analyses were conducted to assess the influence of sociodemographic variables and TPB constructs on cancer screening intentions. Age, female sex, reporting a routine doctor's visit, reported knowledge of physical activity as a lifestyle behavior to reduce cancer risk, and an increased number of motivating factors for engaging in physical activity were significantly associated with higher cancer screening intention (P < 0.001). With the addition of TPB constructs (i.e., subjective norms and perceived behavioral control), the final analytic model accounted for 31% of the variance in intention to screen for cancer. Findings suggest that the TPB could be used to tailor or design asset-based, cancer education interventions to effectively promote age-eligible cancer screenings among physically active adults. Educational content to increase social support for cancer screening and enhance perceived behavioral control to complete screening is essential in this population.

Physically fit with a higher cancer risk? Influences of cervical cancer screening among a sample of physically active women ages 21-49 living in the United States.

To achieve the lowest risk level for various cancers, individuals would engage in several healthy lifestyle behaviors and age-eligible cancer screenings as recommended. Nonetheless, research has largely omitted exploration of concurrent primary and secondary prevention behaviors. This study was designed to explore influences of cervical cancer screening among physically active women who reported participation in recreational sports. U.S. based women between the ages of 21-49, who had never been diagnosed with cancer, were eligible to complete a web-based survey. Logistic regression analyses were conducted using SAS 9.4. On average, women were 31 years of age (N = 394) and self-identified as Black (51.3 %). Although low overall (30.7 %), higher odds of cervical cancer screening were associated with age (OR = 1.06, 95 % CI = 1.03-1.10), employment (OR = 2.43, 95 % CI = 1.14-5.18), knowledge of cancer-related risk behaviors (OR = 4.04, 95 % CI = 1.33-12.28), routine doctor's visit (OR = 4.25, 95 % CI = 1.56-11.54), and team-based vs individual-based sport participation (OR = 1.95, 95 % CI = 1.13-3.34). Our study provides insight into the health profile of physically active women, ages 21-49, as it relates to risks for cervical cancer. Screening uptake among this diverse sample was much lower than the general population and national goals set by Healthy People 2030. Interventions should be tailored to increase knowledge of cancer-related risk behaviors, access to healthcare, and recommended cervical cancer screenings among even assumed-to-be healthy populations.

Reported rationales for HPV vaccination vs. Non-vaccination among undergraduate and medical students in South Carolina.

Objective: We sought to identify factors that influence Human Papillomavirus (HPV) vaccination rates in individuals at two higher education institutions in South Carolina (SC).Participants: We surveyed 1007 students with a mean age and standard deviation of 20.3 ± 3.3 from September 2018 to December 2018.Methods: Participants answered 13 questions, assessing HPV vaccination rates, demographics, and rationales for vaccination vs. non-vaccination.Results: Of 1007 respondents, 700 received HPV vaccination, 165 were unvaccinated, 75 received partial vaccination and 138 were uncertain. Commonalities in HPV vaccination existed between females (p = 0.037), individuals who received standard childhood vaccinations (p = 0.04), and those not native-born in SC (p < 0.001). Of non-vaccinated individuals, 37% "never thought about vaccination," 32% did not perceive a need for vaccination, and 31% reported vaccine safety as reasons for not receiving the vaccine.Conclusions: Promotion of HPV vaccination may benefit from targeting SC natives, males, and individuals who are under-vaccinated or unvaccinated.

Low plasma vitamin D is associated with adverse colorectal cancer survival after surgical resection, independent of systemic inflammatory response.

OBJECTIVE: We assessed the effect of surgical resection of colorectal cancer (CRC) on perioperative plasma vitamin D (25OHD) and C-reactive protein (CRP) level. We investigated the relationship between circulating vitamin D level and CRC survival. DESIGN: We sequentially sampled 92 patients undergoing CRC resection, and measured plasma 25OHD and CRP. For survival analyses, we assayed 25OHD and CRP in two temporally distinct CRC patient cohorts (n=2006, n=2100) and investigated the association between survival outcome, circulating vitamin D and systemic inflammatory response. RESULTS: Serial sampling revealed a postoperative fall (mean 17.3 nmol/L; p=3.6e-9) in plasma 25OHD (nadir days 1-2). CRP peaked 3-5 days postoperatively (143.1 mg/L; p=1.4e-12), yet the postoperative fall in 25OHD was independent of CRP. In cohort analyses, 25OHD was lower in the 12 months following operation (mean=48.8 nmol/L) than preoperatively (54.8 nmol/L; p=1.2e-5) recovering after 24 months (52.2 nmol/L; p=0.002). Survival analysis in American Joint Committee on Cancer stages I-III demonstrated associations between 25OHD tertile and CRC mortality (HR=0.69; 95% CI 0.46 to 0.91) and all-cause mortality (HR=0.68; 95% CI 0.50 to 0.85), and was independent of CRP. We observed interaction effects between plasma 25OHD and rs11568820 genotype (functional VDR polymorphism) with a strong protective effect of higher 25OHD only in patients with GG genotype (HR=0.51; 95% CI 0.21 to 0.81). We developed an online tool for predicted survival (https://apps.igmm.ed.ac.uk/mortalityCalculator/) that incorporates 25OHD with clinically useful predictive performance (area under the curve 0.77). CONCLUSIONS: CRC surgery induces a fall in circulating 25OHD. Plasma 25OHD level is a prognostic biomarker with low 25OHD associated with poorer survival, particularly in those with rs11568820 GG genotype. A randomised trial of vitamin D supplementation after CRC surgery has compelling rationale.

A religiously-tailored, multilevel intervention in African American churches to increase HIV testing: Rationale and design of the Taking It to the Pews cluster randomized trial.

HIV continues to disproportionately impact African American (AA) communities. Due to delayed HIV diagnosis, AAs tend to enter HIV treatment at advanced stages. There is great need for increased access to regular HIV testing and linkage to care services for AAs. AA faith institutions are highly influential and have potential to increase the reach of HIV testing in AA communities. However, well-controlled full-scale trials have not been conducted in the AA church context. We describe the rationale and design of a 2-arm cluster randomized trial to test a religiously-tailored HIV testing intervention (Taking It to the Pews [TIPS]) against a standard information arm on HIV testing rates among AA church members and community members they serve. Using a community-engaged approach, TIPS intervention components are delivered by trained church leaders via existing multilevel church outlets using religiously-tailored HIV Tool Kit materials and activities (e.g., sermons, responsive readings, video/print testimonials, HIV educational games, text messages) to encourage testing. Church-based HIV testing events and linkage to care services are conducted by health agency partners. Control churches receive standard, non-tailored HIV information via multilevel church outlets. Secondarily, HIV risk/protective behaviors and process measures on feasibility, fidelity, and dose/exposure are assessed. This novel study is the first to fully test an HIV testing intervention in AA churches - a setting with great reach and influence in AA communities. It could provide a faith-community engagement model for delivering scalable, wide-reaching HIV prevention interventions by supporting AA faith leaders with religiously-appropriate HIV toolkits and health agency partners.

Autologous breast reconstruction using the immediately lipofilled extended latissimus dorsi flap.

BACKGROUND: The latissimus dorsi flap is a popular choice for autologous breast reconstruction. To dramatically improve volume, we report our experience of using the immediately lipofilled extended latissimus dorsi (ELD) flap and show it as a valid option for autologous breast reconstruction. METHODS: Patients undergoing the procedure between December 2013 and June 2016 were included. Demographic, clinical and operative factors were analysed, together with in-hospital morbidity and duration of postoperative hospital stay. RESULTS: A total of 71 ELD flaps with immediate lipofilling were performed. Forty-five reconstructions were immediate and the remaining 26 delayed. Median (range) volume of autologous fat injected immediately was 171 ml (40-630 ml). Contralateral reductions were performed in 25 patients with the median reduction volume 185 g (89-683 g). Median duration of admission was 6.5 (3-18) days and patients were followed up for 12 months (1-37). Three total flap failures occurred and had to be excised (4%). One haematoma occurred requiring drainage (1%). Signs of infection requiring intravenous antibiotics occurred in five patients (7%). In 5 patients wound dehiscence occurred, and only two of these required resuturing (3%). In total, 7 patients developed a seroma requiring repeated drainage (10%). Three reconstructions experienced mild mastectomy flap necrosis with no needing reoperation (4%). CONCLUSIONS: Our experience represents the largest series to date and shows that in carefully selected patients the technique is safe, can avoid the requirement for implants, and has the potential to streamline the reconstructive journey.

The PC12 cell as model for neurosecretion.

This review attempts to touch on the history and application of amperometry at PC12 cells for fundamental investigation into the exocytosis process. PC12 cells have been widely used as a model for neural differentiation and as such they have been used to examine the effects of differentiation on exocytotic release and specifically release at varicosities. In addition, dexamethasone-differentiated cells have been shown to have an increased number of releasable vesicles with increased quantal size, thereby allowing for an even broader range of applications including neuropharmacological and neurotoxicological studies. PC12 cells exhibiting large numbers of events have two distinct pools of vesicles, one about twice the quantal size of the other and each about half the total releasable vesicles. As will be outlined in this review, these cells have served as an extremely useful model of exocytosis in the study of the latency of stimulation-release coupling, the role of exocytotic proteins in regulation of release, effect of drugs on quantal size, autoreceptors, fusion pore biophysics, environmental factors, health and disease. As PC12 cells have some advantages over other models for neurosecretion, including chromaffin cells, it is more than likely that in the following decade PC12 cells will continue to serve as a model to study exocytosis.

Loaded dopamine is preferentially stored in the halo portion of PC12 cell dense core vesicles.

Large dense core vesicles in rat pheochromocytoma cells are morphologically distinct from dense core vesicles in mast and chromaffin cells in that the dense core occupies a much smaller fraction of the vesicular volume, allowing for a much larger vesicular clear space, or halo. In this work, we present evidence indicating that upon treatment with L-DOPA the majority of the dopamine loaded into these vesicles is preferentially compartmentalized into the halo portion of the vesicle. Amperometry was used to monitor release of loaded neurotransmitter from cells in both isotonic and hypertonic extracellular conditions, with the latter condition causing inhibition of dense core dissociation. In combination with this we have used transmission electron microscopy to determine the morphological characteristics of dense core vesicles before and after treatment with L-DOPA in solutions of varied osmolarity. The results provide a more complete understanding of the complex interaction of molecules within dense core vesicles, suggesting that newly loaded dopamine is located in the halo of the vesicle. This finding has fundamental significance for studies of neurotransmitter release from dense core vesicles, as the core appears to have a function involving more than simple storage of neurotransmitter and associated molecules, and the often overlooked vesicular halo appears to be an important storage compartment for neurotransmitter.

The effects of vesicular volume on secretion through the fusion pore in exocytotic release from PC12 cells.

Many spikes in amperometric records of exocytosis events initially exhibit a prespike feature, or foot, which represents a steady-state flux of neurotransmitter through a stable fusion pore spanning both the vesicle and plasma membranes and connecting the vesicle lumen to the extracellular fluid. Here, we present the first evidence indicating that vesicular volume before secretion is strongly correlated with the characteristics of amperometric foot events. L-3,4-dihydroxyphenylalanine and reserpine have been used to increase and decrease, respectively, the volume of single pheochromocytoma cell vesicles. Amperometry and transmission electron microscopy have been used to determine that as vesicle size is decreased the frequency with which foot events are observed increases, the amount and duration of neurotransmitter released in the foot portion of the event decreases, and vesicles release a greater percentage of their total contents in the foot portion of the event. This previously unidentified correlation provides new insight into how vesicle volume can modulate the activity of the exocytotic fusion pore.

VMAT-Mediated changes in quantal size and vesicular volume.

It has been well established that the volume of secretory vesicles can be modulated. However, we present the first data demonstrating that the amount of transmitter in a vesicle can regulate its volume. Amperometry and transmission electron microscopy have been used to determine that l-3,4-dihydroxyphenylalanine and reserpine increase and decrease, respectively, the volume of single pheochromocytoma cell vesicles as well as their catecholamine content. Because changes in vesicular catecholamine content are tracked by changes in vesicle volume, our results indicate that when quantal size is altered via the vesicular monoamine transporter the concentration of catecholamines within the vesicles remains relatively constant. This previously unidentified cellular response provides new insight into how catecholamines can be packaged in and released from secretory vesicles.

Quantitative and statistical analysis of the shape of amperometric spikes recorded from two populations of cells.

Previously used methods of comparing amperometric spike characteristics from two separate groups of cells have entailed pooling all the values for a spike characteristic from each group of cells and then statistically comparing the two samples. Although this approach has indicated that there are significant differences between the spike characteristics from coloboma and control mouse chromaffin cells, the results are not consistent between experiments. We have reexamined the assumptions of the statistical tests used as well as the variability inherent in amperometric data measured from two groups of cells. Our findings indicate that when comparing amperometric spike characteristics between groups of cells, it is more appropriate to compare samples of mean spike values. This method consistently indicates that there is no difference between coloboma and control amperometric spikes. These results have been validated by using samples of mean spike characteristics to detect changes in the shape of amperometric spikes from both mouse chromaffin cells at 37 degrees C and PC12 cells previously exposed to 50 microM L-3,4-dihydroxyphenylalanine and by the use of an additional analysis method, the nested ANOVA. Together, these results indicate that pooled samples of amperometric spike characteristics can give results that may confound the interpretation of amperometric data.

Calculation of transmitter concentration in individual PC12 cell vesicles with electrochemical data and a distribution of vesicle size obtained by electron microscopy.

A mathematical model is described to accurately calculate vesicle size and neurotransmitter concentration distributions from electrochemical data. This model uses parameters from electrochemical exocytosis data obtained from PC12 cells in culture to calculate a size distribution that is then correlated to the size of vesicles obtained by electron microscopy. The relative standard deviation of the size distribution calculated from electrochemical data is 25% which matches the relative standard deviation of the vesicle size distribution measured by electron microscopy. The distribution calculated from electrochemical data is normalized to the vesicle size distribution of PC12 cell vesicles obtained from electron microscopy. Calculation of a vesicular catecholamine concentration histogram from the normalized size data and electrochemical parameters is then possible for individual exocytosis events. The average vesicular catecholamine concentration for PC12 cells as calculated by this method is 148+/-7 mM. More importantly, there is a distribution of concentration rather than a constant value. Additionally, the model permits evaluation of the concentration of transmitter in each individual vesicle and vesicle size for each vesicle from electrochemical data when the overall vesicle size distribution is known.

Voltammetric and pharmacological characterization of dopamine release from single exocytotic events at rat pheochromocytoma (PC12) cells.

Although rat pheochromocytoma (PC12) neurotransmitter storage vesicles are known to contain a variety of neurotransmitters including catecholamines, there is little evidence that the molecular species detected during amperometric monitoring of exocytosis is a catecholamine. Rather, as these are catecholamine-containing cells, one assumes catecholamines are released. Additionally, although the total amount of transmitter released can be quantified, it has been extremely difficult to evaluate the concentration at the point of release for each exocytosis event. Interpreting voltammograms obtained in the attoliter volume affected between the electrode and the cell and defined by the size of the exocytosis pore during exocytosis is an extreme analytical challenge. Here we use voltammetry of approximately 10(-19) mol released from individual exocytosis events to identify, along with pharmacological evidence, the released compound at PC12 cells as a catecholamine, most likely dopamine. The area of the electrode at which oxidation occurs following an exocytosis event is proportional to the temporal delay prior to acquisition of a voltammogram. This model allows determination of relative concentrations from individual release events and has been used to examine events at control cells and cells incubated with the dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA). Exposure to L-DOPA (100 microM for 1 h) results in 145 detectable events for 11 cells compared to 77 events for 29 control cells, clearly indicating that vesicles can be "loaded" with dopamine. However, the concentrations measured at the electrode surface provide similar distributions for both L-DOPA-treated and control cells. Cyclic voltammetric measurements of relative concentration for zeptomole levels of transmitter in attoliter volumes provide evidence that loading vesicles by increased transmitter synthesis does not lead to elevated concentrations at individual release sites.

Quantitative measurements of released amines from individual exocytosis events.

Chemical analysis of single cells is an area of great interest in the biological sciences. Single-cell systems are being utilized as a model to understand in vivo processes better. One method that is moving to the forefront in cellular analysis is electrochemistry. Owing to their rapid response time and small dimensions, voltammetric microelectrode techniques, such as amperometry and fast-scan voltammetry, have made it possible to monitor minute amounts of biological compounds and transiently occurring chemical events in cellular systems. The application of these methods to the quantitation of individual vesicular release events from single cells is overviewed here. The application of electrochemical monitoring to several types of cultured cells, including bovine adrenal chromaffin cells, rat pheochromocytoma (PC12) cells, beige mouse mast cells, superior cervical ganglion neurons, and human pancreatic beta-cells, as well as to the invertebrate systems, the leech Hirudo medicinalis, and pond snail Planorbis corneus has provided a wealth of new information concerning exocytosis. Results obtained from the studies highlight the potential of electrochemical techniques in cellular analysis to contribute to our understanding of molecular and pharmacological effects on exocytosis. This article overviews work done on all the above cell types with an emphasis on PC12 cells.

Chemical analysis of single cells and exocytosis.

Recent advances in the development of microscale analytical techniques have allowed minute amounts of compounds of biological interest to be monitored in microenvironments. Microcolumn separation techniques, such as microcolumn liquid chromatography and capillary electrophoresis, provide a means of obtaining high-efficiency separations of analytes in picoliter to femtoliter volume samples. Voltammetric microelectrode techniques, such as amperometry and fast-scan cyclic voltammetry, are ideally suited for monitoring transiently occurring chemical events in cellular and subcellular processes owing to their rapid response times and small structural dimensions. The principles and applications of these techniques in single-cell analysis are discussed throughout this review. Multicomponent separations and quantitations of large invertebrate neurons of the land snail Helix neurons and the pond snail Planorbis corneus dopamine neurons, and of small mammalian cells, bovine adrenal cells, rat PC12 cells, and human lymphocytes, by use of microcolumn liquid chromatography and capillary electrophoresis are presented. Electrochemical monitoring of neurotransmitter exocytosis from single adrenal cells, from PC12 cells, and from the cell body of the Planorbis dopamine neuron is highlighted. Results obtained from both separation and voltammetric techniques in single-cell analyses will provide a better understanding of cellular and/or neuronal chemistry and biology in complicated living environments.

Electrochemical monitoring of bursting exocytotic events from the giant dopamine neuron of Planorbis corneus.

We have discovered a neuronal system that fires bursting exocytotic events. In the giant dopamine neuron of the fresh water snail Planorbis corneus, bursting exocytotic events are evoked following in situ stimulation with elevated potassium. Amperometric detection using carbon fiber microelectrodes, which provides high temporal resolution, has been used to record exocytotic events released from the neuron. Evaluation of the time interval between consecutive exocytotic events (inter-spike interval) recorded from about 80% of the neurons reveals the occurrence of distinct bursting patterns defined by transients having an equal interval among them. Statistical analysis of these bursting exocytotic events shows three distinct distributions of inter-spike intervals with mid points occurring at 5, 22 and 45 ms. This bursting release behavior is not observed from cultured pheochromocytoma cells although they show calcium-dependent exocytosis following in situ stimulation with elevated potassium. Our data appear to indicate that the Planorbis dopamine neuron in vivo is actively involved in specific modes of neural communication and may represent an important phenomenon in understanding single cell activities.

Vesicular quantal size measured by amperometry at chromaffin, mast, pheochromocytoma, and pancreatic beta-cells.

Amperometric detection of exocytosis at single chromaffin cells has shown that the distribution of spike areas, or quantal size, is dependent on the volume and catecholamine concentration of individual secretory vesicles. The present work offers an alternate, simplified model to analyze the current spikes due to single exocytotic events. When the cube root of these spike areas is plotted as a histogram, a Gaussian distribution is obtained for chromaffin cells and also mast, pheochromocytoma, and pancreatic beta-cells. It was found that the relative SD of these distributions is similar to that for the vesicular radii, which also have a Gaussian distribution in all four cell types. In addition, this model was used to evaluate conditions where the quantal size of individual events was altered. When chromaffin cells were maintained in culture for < 6 days, spikes of approximately double the quantal size were obtained on repeated exposure to 60 mM K+. The results suggest a heterogeneous distribution of catecholamine-containing vesicles at later days in culture is responsible for this alteration.