Worldwide Early Impact of COVID-19 on Dialysis Patients and Staff and Lessons Learned: A DOPPS Roundtable Discussion

As the worst global pandemic of the past century, coronavirus disease 2019 (COVID-19) has had a disproportionate effect on maintenance dialysis patients and their health care providers. At a virtual roundtable on June 12, 2020, Dialysis Outcomes and Practice Patterns Study (DOPPS) investigators from 15 countries in Asia, Europe, and the Americas described and compared the effects of COVID-19 on dialysis care, with recent updates added. Most striking is the huge difference in risk to dialysis patients and staff across the world. Per-population cases and deaths among dialysis patients vary more than 100-fold across participating countries, mirroring burden in the general population. International data indicate that the case-fatality ratio remains at 10% to 30% among dialysis patients, confirming the gravity of infection, and that cases are much more common among in-center than home dialysis patients. This latter finding merits urgent study because in-center patients often have greater community exposure, and in-center transmission may be uncommon under optimal protocols. Greater telemedicine use is a welcome change here to stay, and our community needs to improve emergency planning and protect dialysis staff from the next pandemic. Finally, the pandemic's challenges have prompted widespread partnering and innovation in kidney care and research that must be sustained after this global health crisis.

International Anemia Prevalence and Management in Peritoneal Dialysis Patients

Background:The optimal treatment for managing anemia in peritoneal dialysis (PD) patients and best clinical practices are not completely understood. We sought to characterize international variations in anemia measures and management among PD patients.Methods:The Peritoneal Dialysis Outcomes and Practice Patterns Study (PDOPPS) enrolled adult PD patients from 6 countries from 2014 to 2017. Hemoglobin (Hb), ferritin levels, and transferrin saturation (TSAT), as well as erythropoiesis stimulating agents (ESAs) and iron use were compared cross-sectionally at study enrollment in Australia and New Zealand (A/NZ), Canada, Japan, the United Kingdom (UK), and the United States (US).Results:Among 3,603 PD patients from 193 facilities, mean Hb ranged from 11.0 - 11.3 g/dL across countries. The majority of patients (range 53% - 59%) had Hb 10 - 11.9 g/dL, with 4% - 12% patients ≥ 13 g/dL and 16% - 23% < 10 g/dL. Use of ESAs was higher in Japan (94% of patients) than elsewhere (66% - 79% of patients). In the US, 63% of patients had a ferritin level > 500 ng/mL, compared with 5% - 38% in other countries. In the US and Japan, 87% - 89% of PD patients had TSAT ≥ 20%, compared with 73% - 76% in other countries. Intravenous (IV) iron use within 4 months of enrollment was higher in the US (55% of patients) than elsewhere (6% - 17% patients).Conclusions:In this largest international observational study of anemia and anemia management in patients receiving PD, comparable Hb levels across countries were observed but with notable differences in ESA and iron use. Peritoneal dialysis patients in the US have higher ferritin levels and higher IV iron use than other countries.

Anemia and iron deficiency among chronic kidney disease Stages 3-5ND patients in the Chronic Kidney Disease Outcomes and Practice Patterns Study: often unmeasured, variably treated

Background

International variation in anemia assessment and management practices in chronic kidney disease (CKD) is poorly understood.

Methods

We performed a cross-sectional analysis of anemia laboratory monitoring, prevalence and management in the prospective Chronic Kidney Disease Outcomes and Practice Patterns Study (CKDopps). A total of 6766 participants with CKD Stages 3a–5ND from nephrology clinics in Brazil, France, Germany and the USA were included.

Results

Among patients with anemia (hemoglobin <12 g/dL), 36–58% in Brazil, the USA and Germany had repeat hemoglobin measured and 40–61% had iron indices measured within 3 months of the index hemoglobin measurement. Anemia was more common in the USA and Brazil than in France and Germany across CKD stages. Higher ferritin and lower iron saturation (TSAT) levels were observed with lower hemoglobin levels, and higher ferritin with more advanced CKD. The proportion of anemic patients with ferritin <100 ng/mL or TSAT <20% ranged from 42% in Brazil to 53% in France and Germany, and of these patients, over 40% in Brazil, Germany and the USA, compared with 27% in France, were treated with oral or intravenous iron within 3 months after hemoglobin measurement. The proportion of patients with hemoglobin <10 g/dL treated with erythropoiesis-stimulating agents ranged from 28% in the USA to 57% in Germany.

Conclusions

Hemoglobin and iron stores are measured less frequently than per guidelines. Among all regions, there was a substantial proportion of anemic patients with iron deficiency who were not treated with iron, highlighting an area for practice improvement in CKD care.

Education and screening for chronic kidney disease in Indian youth: pilot program results

BACKGROUND

There is a paucity of information on kidney education and screening programs in Indian youth.

METHODS

Participants (n=2,158) from Chennai colleges were educated about the kidneys and chronic kidney disease (CKD) and screened in a pilot program from April to May 2013. This entailed: 1) a presentation and educational video and 2) an on-site assessment of weight, blood pressure, and demographic information. Urinalysis (UA) kits were distributed and returned in ≤48 hours. We examined participant characteristics and their association with dipstick proteinuria using logistic regression.

RESULTS

The mean (standard deviation [SD]) age was 18.9 (1.6) years, and 1,451 (68%) were men. Mean (SD) body mass index (BMI) was 21.9 (4.3) kg/m²; 745 (36%) had a BMI consistent with being overweight or obese. Mean (SD) systolic blood pressure (SBP) was 118.7 (13.1) mm Hg, and 94 (5%) of the participants had SBP ≥140. Mean (SD) diastolic blood pressure (DBP) was 70.9 (11.4) mm Hg, with 119 participants (6%) having ≥90 mm Hg. A total of 136 participants had glycosuria (UA≥1+) and 120 (6%) had proteinuria (UA≥1+). In unadjusted analyses, sex (odds ratio [OR]=1.64 [confidence interval, CI 1.06-2.55]; p=0.026 men vs. women) and age (OR=1.13 per year [CI 1.01-1.26]; p=0.032) were significantly associated with proteinuria. In the analysis adjusted for age, sex, SBP, DBP, glycosuria, and BMI, age remained independently associated with higher odds for proteinuria (OR=1.14 per year [1.02-1.29]; p=0.026). Males showed a trend of higher risk compared with women (OR=1.57 [CI 1.00-2.50]; p=0.051).

CONCLUSION

This education and screening pilot program in a population of college students offers unique opportunities for identification, education, and early intervention for CKD.

Understanding the medical marriage: physicians and their partners share strategies for success

PURPOSE

Physicians and their spouses experience challenges to their relationships, some of which are shared with the general population and others of which are unique to the field of medicine. Trainees and junior faculty members remain curious about how they will balance their careers alongside marriage and family obligations. This study explores the challenges and strengths of dual- and single-physician relationships.

METHOD

In 2009, using appreciative inquiry as a theoretical framework, the authors conducted in-depth qualitative interviews with 25 individuals: 12 women and 13 men; 10 from dual-physician and 15 from single-physician relationships. A phenomenological analytic approach was used to arrive at the final themes.

RESULTS

Four themes emerged during the interviews: "We rely on mutual support in our relationships," "We recognize the important roles of each family member," "We have shared values," and "We acknowledge the benefit of being a physician to our relationships."

CONCLUSIONS

These findings illustrate that physicians identify strategies to navigate the difficult aspects of their lives. Learn ing from others' best practices can assist in managing personal relationships and work-life balance. These data can also be useful when counseling physicians on successful relationship strategies. As systems are developed that improve wellness and focus on role models for work-life balance, it will be important for this topic to be integrated into formal curricula across the continuum of medical education.

A successful faculty development program for implementing a sociocultural ePortfolio assessment tool

Portfolios are emerging as a tool for documenting learning progression and assessing competency. ePortfolios are appealing as a portable and fluid means of documenting both learning and relevant experiences in a large number of students. Competence and learning can be especially difficult to document in important aspects of education and training, such as patient-centeredness, the cultural context of disease, and social determinants of health that do not lend themselves to fact-based assessment methods. Successful implementation of a method such as an ePortfolio requires explicit faculty development, as many faculty members have limited expertise with modern educational assessment technology. As part of the authors' introduction of a Sociocultural ePortfolio Assessment Tool in the undergraduate medical curriculum, three faculty development workshops were held to expand faculty skills in using this technology. In addition to gaining comfort using a new Web-based technology, faculty members also needed to develop skills with providing mentored feedback and stimulating student reflection. Workshops were modeled after other successful programs reported in the literature and allowed faculty to develop a structured format for evaluating student content. Faculty members were given multiple opportunities to practice their newly developed skills providing mentored reflections using an ePortfolio. The workshop evaluations were positive, suggesting that faculty participation in the workshops were a necessary component for them to develop sufficient assessment skills for providing mentored reflection. Faculty members who participated in this program-whether or not they had content expertise in sociocultural medicine-valued the hands-on faculty development program.

The impact of facilitation of small-group discussions of psychosocial topics in medicine on faculty growth and development

PURPOSE

To use qualitative analysis of interview transcripts with clinician-educators who facilitate small-group discussions on psychosocial themes--including doctoring--to answer the question, "What impact does facilitating small-group discussions of the patient's experience with chronic illness, the doctor-patient relationship, and doctoring have on faculty instructors' attitudes regarding their roles as clinicians and teachers?"

METHOD

In 2006, in-depth, face-to-face interviews using an open-ended question format were conducted with individual faculty small-group instructors teaching in the Family Centered Experience and Longitudinal Case Studies courses at the University of Michigan Medical School. Interview transcripts were analyzed using grounded theory methodology to identify emerging themes. Accuracy of interpretations and saturation of themes was confirmed by repeated contextual reading of the transcripts.

RESULTS

Several major thematic codes emerged from the data. Facilitation of small-group discussions of psychosocial topics and doctoring fostered reflective approaches to patient care and teaching; enhanced interpersonal relationships between facilitators and their students, colleagues, and patients; and acted as a source of fulfillment and renewal among faculty facilitators.

CONCLUSIONS

Small-group teaching of the art of doctoring may stimulate personal and professional growth among faculty facilitators and renewed interest in teaching and patient care.

Blood content of asymmetric dimethylarginine: new insights into its dysregulation in renal disease

BACKGROUND

Plasma asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is significantly elevated in patients with kidney disease and is a potential risk factor for cardiovascular disease. Here, we tested whether human whole blood (WB), as in rodent blood, can accumulate free ADMA and whether this accumulation is a function of disease burden.

METHODS

In 16 healthy control subjects (CO), 18 patients with ESRD and 18 matched hypertensive patients with normal renal function (HTN), we compared using high-pressure liquid chromatography baseline plasma and WB supernatant (WBSUP) ADMA and symmetrical dimethylarginine (SDMA) concentrations and accumulation during a 5-h incubation. We measured protein turnover in incubated WBSUP to determine if proteolytic processes drive ADMA accumulation.

RESULTS

Elevated plasma ADMA was confirmed in ESRD and HTN populations while basal WBSUP ADMA was significantly higher in ESRD subjects than controls (P = 0.05 versus CO; P = 0.02 versus HTN). Plasma SDMA followed a similar pattern. Incubation of WBSUP resulted in ADMA release from protein-incorporated stores while SDMA was unaffected. ADMA accumulation in ESRD samples was significantly greater than that in HTN (P = 0.03). CO and HTN men showed significantly greater ADMA accumulation than women (P = 0.01 and P = 0.003, respectively) but no gender difference was observed in the ESRD group (P = 0.26). ADMA accumulation correlated with ex vivo protein turnover (R = 0.76, P < 0.0001).

CONCLUSIONS

Human blood is capable of releasing physiologically significant quantities of ADMA via proteolytic pathways. Dysregulated ADMA release from WB reservoirs may contribute to the distinctly high plasma ADMA levels in ESRD populations.

Quality of life in chronic kidney disease (CKD): a cross-sectional analysis in the Renal Research Institute-CKD study

BACKGROUND

Health-related quality of life (QOL) is an important measure of how disease affects patients' lives. Dialysis patients have decreased QOL relative to healthy controls. Little is known about QOL in patients with chronic kidney disease (CKD) before renal replacement therapy.

METHODS

The Medical Outcomes Study Short Form-36 (SF-36), a standard QOL instrument, was used to evaluate 634 patients (mean glomerular filtration rate [GFR], 23.6 +/- 9.6 mL/min/1.73 m2 [0.39 +/- 0.16 mL/s/1.73 m2]) enrolled in a 4-center, prospective, observational study of CKD. SF-36 scores in these patients were compared with those in a prevalent cohort of hemodialysis (HD) patients and healthy controls (both from historical data). QOL data also were analyzed for correlations with GFR and albumin and hemoglobin levels in multivariable analyses.

RESULTS

Patients with CKD had higher SF-36 scores than a large cohort of HD patients (P < 0.0001 for 8 scales and 2 summary scales), but lower scores than those reported for the US adult population (P < 0.0001 for 7 of 8 scales and 1 of 2 summary scales). Patients with CKD stage 4 had lower QOL scores than patients with CKD stage 5, although differences were not significant. Hemoglobin level was associated positively with higher mental and physical QOL scores (P < 0.05) in all individual and component scales except Pain.

CONCLUSION

SF-36 scores were higher in this CKD cohort compared with HD patients, but lower than in healthy controls. GFR was not significantly associated with QOL. Hemoglobin level predicted both physical and mental domains of the SF-36. Longitudinal studies are needed to define at-risk periods for decreases in QOL during progression of CKD.

RENAL RESEARCH INSTITUTE SYMPOSIUM: The Longitudinal Chronic Kidney Disease Study: A Prospective Cohort Study of Predialysis Renal Failure

Chronic kidney disease (CKD) is a significant public health problem: every year the number of Americans living with CKD and requiring renal replacement therapy increases. In addition, individuals with CKD have substantially increased morbidity and mortality compared to the general population. The Longitudinal Chronic Kidney Dialysis (LCKD) Study is a multicenter, prospective, observational study of patients with moderate to severe CKD that was designed to better describe the course of the disease and the determinants of patient outcomes. Patients with moderate to severe CKD (glomerular filtration rate [GFR] < 60 ml/min/m2) from four academic nephrology clinics were enrolled between 2000 and 2002. Special cardiac and vascular testing has recently commenced as phase II of this study. Areas that have been or are currently being studied include anemia management, health-related quality of life (HRQOL), medication use, and markers of cardiovascular disease. This article describes the LCKD Study in the context of current knowledge of CKD.

Prolactin-induced cell proliferation in PC12 cells depends on JNK but not ERK activation

The effects of pituitary and extrapituitary prolactin include cellular proliferation and differentiation. PC12 cells was used as a model to delineate respective signaling of prolactin. Prolactin acted as a mitogen for undifferentiated PC12 cells, as measured by significant increases in bromodeoxyuridine incorporation and in cell numbers, with an efficacy equal to epidermal growth factor. Both the long and short form of the prolactin receptor was expressed, yet only the long isoform was tyrosine-phosphorylated upon agonist binding. Functional prolactin receptor signaling was further demonstrated in the activation of JAK2 and phosphorylation activation of the transcription factors Stat1, -3, and -5a. Surprisingly, prolactin stimulated a sustained activation of Raf-B, without activation of the MAP kinases ERK1 or -2. Instead, in solid phase kinase assays using a glutathione S-transferase-c-Jun fusion protein (amino acids 1-79) as the substrate, a significant activation of the mitogen-activated protein Janus kinase (c-Jun N-terminal kinase; JNK) was observed. The prolactin-induced activation of JNK was prolonged and accompanied by a significant increase in c-Jun mRNA abundance and c-Jun protein synthesis. Moreover, analysis of bromodeoxyuridine incorporation at the single cell level revealed that epidermal growth factor-dependent incorporation was inhibited by PD98059 and independent of SB203580, whereas prolactin-induced incorporation was ERK and mitogen-activated protein kinase p38 independent but was abolished with JNK inhibition by 30 microm SB203580. Our studies suggest that prolactin may have a role in the growth of PC12 cells, where it stimulates concurrent mitogenic and differentiation-promoting signaling pathways.

Differential regulation of phenylethanolamine N-methyltransferase expression in two distinct subpopulations of bovine chromaffin cells

Chromaffin cells were isolated from bovine adrenal glands and fractionated into two distinct subpopulations by density gradient centrifugation on Percoll. Cells in the more dense fraction stored epinephrine (E) as their predominant catecholamine (81% of total catecholamines), contained high levels of phenylethanolamine N-methyltransferase (PNMT) activity, and exhibited intense PNMT immunoreactivity. This population of chromaffin cells was termed the E-rich cell population. Cells in the less dense fraction, the norepinephrine (NE)-rich cell population, stored predominantly NE (75% of total catecholamines). Although the NE-rich cells had only 3% as much PNMT activity as did the E-rich cells, 20% of the NE-rich cells were PNMT immunoreactive. This suggested that the PNMT-positive cells in the NE-rich cell cultures contained less PNMT per cell than did E-rich cells and may not be typical adrenergic cells. The regulation of PNMT mRNA levels and PNMT activity in primary cultures of E-rich and NE-rich cells was compared. At the time the cells were isolated, PNMT mRNA levels in NE-rich cells were approximately 20% of those in E-rich cells; within 48 h in culture, PNMT mRNA in both populations declined to almost undetectable levels. Treatment with dexamethasone increased PNMT mRNA levels and PNMT activity in both populations. In E-rich cells, dexamethasone restored PNMT mRNA to the level seen in freshly isolated cells and increased PNMT activity twofold. In NE-rich cells, dexamethasone increased PNMT mRNA to levels twice those found in freshly isolated cells and increased PNMT activity sixfold. Cycloheximide blocked the effects of dexamethasone on PNMT mRNA expression in NE-rich cells but had little effect in E-rich cells. Angiotensin II, forskolin, and phorbol 12,13-dibutyrate elicited large increases in PNMT mRNA levels in E-rich cells but had no effect in NE-rich cells. Our data suggest that PNMT expression is regulated differently in the two chromaffin cell subpopulations.

Differences in the composition of chromaffin granules in adrenaline and noradrenaline containing cells of bovine adrenal medulla

Several constituents of chromaffin granules were quantitatively determined in noradrenaline and adrenaline cells purified from bovine adrenal medulla. As far as secretory peptides are concerned noradrenaline granules contained slightly more secretogranin II, but much less chromogranin A than adrenaline granules. This can be explained by the dependence of the biosynthesis of chromogranin A on corticosteroids. Proteolytic processing of chromogranin A and secretogranin II was higher in noradrenaline cells which was paralleled by a higher content of the prohormone convertase PC2. Noradrenaline granules also contained a higher concentration of the vesicular monoamine transporter (vMAT2). No differences were found for dopamine beta-hydroxylase, prohormone convertase PC1, carboxypeptidase H and synaptophysin. These results indicate that the secretory cocktail of peptides released from these cells differs significantly between adrenaline and noradrenaline storing cells.

Inhibition of lymphocyte activation by catecholamines: evidence for a non-classical mechanism of catecholamine action

The effects of noradrenaline and other adrenergic agonists on lymphocyte activation were studied. Spleen and thymus cells from BALB/c mice were stimulated by mitogens and lymphocyte activation was monitored by measuring the incorporation of [methyl-3H]thymidine into DNA. Noradrenaline, adrenaline, isoproterenol and dopamine all inhibited the activation of spleen and thymus cells by concanavalin A, a T-cell specific mitogen, and the activation of spleen cells by lipopolysaccharide, a T-independent B-cell mitogen. The various catecholamines were approximately equipotent, having IC50 of approximately 10 microM. alpha-adrenergic agonists (phenylephrine, clonidine) did not inhibit lymphocyte activation. Noradrenaline, adrenaline and isoproterenol also inhibited DNA synthesis in S49 T lymphoma cells. The effects of adrenergic receptor antagonists on lymphocyte function were also studied. The inhibition of lymphocyte activation by catecholamines could not be reversed by antagonists to beta-adrenergic receptors (propranolol), alpha-adrenergic receptors (phentolamine), or dopaminergic receptors (haloperidol). Experiments with human peripheral blood leucocytes revealed that, as with murine cells, the beta-adrenergic antagonists propranolol and nadalol did not affect the catecholamine-mediated inhibition of lymphocyte activation. Although lymphocytes contain beta-adrenergic receptors that are coupled to adenylyl cyclase activity, catecholamines appear to inhibit murine lymphocyte activation by a mechanism that is independent of these or other classical adrenergic receptors.

Neurotransmitter suppression of the in vitro generation of a cytotoxic T lymphocyte response against the syngeneic MOPC-315 plasmacytoma

We have previously shown that, as a consequence of low-dose melphalan (L-phenylalanine mustard (L-PAM) therapy, the hitherto immunosuppressed spleen cells from BALB/c mice bearing a large MOPC-315 tumor (in contrast to spleen cells from normal mice) acquire the ability to generate a greatly enhanced anti-MOPC-315 cytotoxic T lymphocyte (CTL) response upon in vitro stimulation with MOPC-315 tumor cells. Here we show that the catecholamines norepinephrine, epinephrine, and isoproterenol suppressed the in vitro generation of anti-MOPC-315 cytotoxicity by spleen cells from mice that had just completed the eradication of a large MOPC-315 tumor following low-dose L-PAM therapy (L-PAM TuB spleen cells), as well as by spleen cells from normal mice. In contrast to the marked suppression obtained with catecholamines, the cholinergic agonist carbachol had no effect on the in vitro generation of splenic anti-MOPC-315 cytotoxicity. The inhibitory effect of the catecholamines was "mimicked" by the membrane penetrating analog of cAMP, dibutyryl-cAMP, and by cholera toxin at concentrations that stimulate the endogenous production of cAMP. The beta-adrenergic receptor antagonist propranolol did not block norepinephrine-induced inhibition of the generation of anti-MOPC-315 cytotoxicity by either normal or L-PAM TuB spleen cells. Since the curative effectiveness of low-dose L-PAM therapy for MOPC-315 tumor bearers requires the participation of CD8+ T cells that exploit a CTL response in tumor eradication, it is conceivable that norepinephrine may reduce the therapeutic outcome of low-dose chemotherapy by inhibiting the acquisition of CTL activity.

Glucocorticoids enhance histamine-evoked catecholamine secretion from bovine chromaffin cells

The synthetic glucocorticoid dexamethasone enhanced histamine-evoked catecholamine secretion from cultured bovine chromaffin cells. Dexamethasone enhanced the effects of histamine on both adrenergic (epinephrine-rich) and noradrenergic (norepinephrine-rich) chromaffin cells but had a more dramatic effect on noradrenergic cells. Histamine-evoked secretion in noradrenergic cells appeared to become rapidly inactivated, whereas the rate of secretion in adrenergic cells was nearly constant for up to 2 h; dexamethasone treatment attenuated the inactivation seen in noradrenergic cells. The effect of dexamethasone appeared after a lag of several hours and was maximal by 24 h. The EC50 for dexamethasone was approximately 1 nM. The effect of dexamethasone was mimicked by the glucocorticoid agonist RU 28362 and was blocked by the antagonist RU 38486, indicating that the effects of these steroids were mediated by the glucocorticoid or type II corticosteroid receptor. Histamine-evoked catecholamine secretion in both dexamethasone-treated and untreated cells was blocked by the H1 histamine receptor antagonist mepyramine but was not affected by the H2 antagonist cimetidine; thus, dexamethasone appeared to enhance an H1 receptor-mediated process. In the absence of glucocorticoids, H1 receptor mRNA levels were higher in adrenergic than in noradrenergic cells. Dexamethasone increased H1 receptor mRNA levels in both cell types. The increased expression of H1 receptors presumably contributes to the enhancement of histamine-evoked catecholamine secretion by glucocorticoids. Glucocorticoids may play a physiological role in modulating the responsiveness of chromaffin cells to histamine and other stimuli.

1,25(OH)2 vitamin D3 activates PKC-alpha in Caco-2 cells: a mechanism to limit secosteroid-induced rise in [Ca2+]i

Our laboratory recently reported that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] rapidly increases the breakdown of membrane phosphoinositides, raises intracellular calcium concentration ([Ca2+]i), and translocates protein kinase C (PKC) from the cytosolic to the particulate fraction of Caco-2 cells. In the present experiments, we found that Caco-2 cells contained predominantly the alpha- and zeta-isoforms of PKC, with minimally detectable amounts of PKC-beta and -epsilon by Western blotting. 1,25(OH)2D3 and the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) each caused time-dependent translocations of PKC-alpha, but not PKC-zeta. TPA treatment of these cells for 24 h induced a significant concentration-dependent downregulation of PKC-alpha, but not PKC-zeta. Since PKC inhibits phospholipase C-induced mobilization of Ca2+ in other cells, we examined the effects of staurosporine and H-7, PKC inhibitors, and TPA on 1,25(OH)2D3-stimulated increase in [Ca2+]i. As previously demonstrated by our laboratory, 1,25(OH)2D3 caused a biphasic increase in [Ca2+]i, with an initial elevation (transient phase) followed by a sustained increase (plateau phase). We previously demonstrated that the transient phase is mediated, at least in part, by an increase in inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] stimulated by the secosteroid. Acute pretreatment with staurosporine or H-7 caused a significant stimulation, whereas acute TPA pretreatment caused a significant inhibition of the 1,25(OH)2D3-induced increase in the transient phase of [Ca2+]i. Preincubation of Caco-2 cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxy-methyl ester (BAPTA-AM) abolished both the rise in [Ca2+]i and the increase in particulate-associated PKC-alpha stimulated by 1,25(OH)2D3. Moreover, downregulation of PKC-alpha by chronic TPA treatment significantly augmented the transient phase of the 1,25(OH)2D3-stimulated rise in [Ca2+]i but had no effect on the 1,25(OH)2D3-induced change in Ins(1,4,5)P3 concentration. Furthermore, in these PKC-alpha downregulated cells staurosporine no longer increased the secosteroid-stimulated transient rise in [Ca2+]i. These results indicate that 1,25(OH)2D3, which increases [Ca2+]i and diacylglycerol, activates PKC-alpha, but not PKC-zeta. The alpha-isoform, in turn, limits the secosteroid-stimulated rise in [Ca2+]i, at a step distal to Ins(1,4,5)P3 accumulation in Caco-2 cells.

Tetraethylammonium selectively stimulates secretion from noradrenergic bovine chromaffin cells

1. The effects of tetraethylammonium chloride (TEA) on catecholamine secretion from primary cultures of noradrenaline-rich (noradrenergic) and adrenaline-rich (adrenergic) bovine chromaffin cells were studied. TEA stimulated catecholamine secretion from both cell types but was a much more effective secretory stimulus for noradrenergic cells. 2. TEA-induced catecholamine secretion was dependent on extracellular Ca2+, was partially inhibited by nifedipine and by tetrodotoxin, and was potentiated by ouabain. Other K+ channel blocking agents including 4-aminopyridine, glibenclamide, and tolbutamide did not stimulate catecholamine secretion. 3. TEA had no effect on Ca(2+)-induced secretion from digitonin-permeabilized chromaffin cells. 4. TEA presumably evokes secretion by inhibiting K+ channels, depolarizing chromaffin cells, and activating voltage-gated Ca2+ channels in the cells. Noradrenergic cells appear to be more sensitive to K+ channel inhibition than are adrenergic cells. 5. The secretory response of the chromaffin cells to TEA increased with time in culture. 6. In addition to being a more effective secretagogue in noradrenergic cells, TEA was also more effective in stimulating catecholamine synthesis in these cells.

Staurosporine activates a 60,000 M(r) protein kinase in bovine chromaffin cells that phosphorylates myelin basic protein in vitro

Bovine chromaffin cells contain a family of renaturable protein kinases. One of these, a 60,000 M(r) kinase (PK60) that phosphorylated myelin basic protein in vitro, was activated fourfold when cells were treated with the protein kinase inhibitor staurosporine. Because staurosporine inhibits protein kinase C, the role of this kinase in the regulation of PK60 activity was investigated. Fifty nanomolar staurosporine produced half-maximal inhibition of protein kinase C activity in chromaffin cells, whereas approximately 225 nM staurosporine was required to induce half-maximal activation of PK60. Other protein kinase C inhibitors, H-7 and K-252a, did not mimic the effect of staurosporine on PK60 activity. Chromaffin cells have three protein kinase C isoforms: alpha, epsilon, and zeta. Prolonged treatment with phorbol esters depleted the cells of protein kinase C alpha and epsilon, but not zeta. Neither activation nor depletion of protein kinase C affected the basal activity of PK60. Moreover, staurosporine activated PK60 in cells depleted of protein kinase C alpha and epsilon; thus, staurosporine appeared to activate PK60 by a mechanism that does not require these protein kinase C isoforms. Incubation of cell extracts with staurosporine in vitro did not activate PK60. Incubation of these extracts with adenosine 5'-O-(3-thiotriphosphate), however, caused a twofold activation of PK60. Although this suggests that PK60 activity is regulated by phosphorylation, the mechanism by which staurosporine activates PK60 is not known. Staurosporine has been reported to promote neurite outgrowth from chromaffin cells. The role of PK60 in mediating the effects of staurosporine on chromaffin cell function remains to be determined.

Histamine evokes greater increases in phosphatidylinositol metabolism and catecholamine secretion in epinephrine-containing than in norepinephrine-containing chromaffin cells

Chromaffin cells have H1 histamine receptors. Histamine, acting at these receptors, increases the metabolism of inositol-containing phospholipids and stimulates catecholamine secretion from chromaffin cells. We have investigated the effects of histamine and other agents on the accumulation of inositol monophosphate (InsP1) and catecholamine secretion in purified cultures of norepinephrine-containing and epinephrine-containing bovine chromaffin cells. Histamine-stimulated InsP1 accumulation in epinephrine cells was three times greater than that in norepinephrine cells. In contrast, bradykinin caused roughly equivalent increases in InsP1 accumulation in the two chromaffin cell subtypes. Histamine-stimulated catecholamine secretion was also greater in epinephrine cells than in norepinephrine cells, whereas high K+, bradykinin, phorbol 12,13-dibutyrate, and angiotensin II all caused greater secretion from norepinephrine cells than from epinephrine cells. The density of H1 receptors in epinephrine cells was approximately three times greater than that in norepinephrine cells. The greater density of H1 receptors on epinephrine cells may account for the greater effects of histamine on InsP1 accumulation and catecholamine secretion in these cells.

Polyoma-induced neoplasms of the mouse adrenal medulla. Characterization of the tumors and establishment of cell lines

BACKGROUND

Pheochromocytomas that are usually noradrenergic arise commonly in the adult rat adrenal medulla. The widely studied PC12 cell line, that is representative of these rat adrenal tumors, is also noradrenergic. The reasons for the absence of epinephrine production by most rat pheochromocytoma cells are unknown, and there are currently no adrenergic adrenal medullary cell lines. Pheochromocytomas are rare in mice.

EXPERIMENTAL DESIGN

Tumors induced by polyoma virus in the adrenal medullas of postnatal mice were studied immunocytochemically for catecholamine biosynthetic enzymes in order to determine how their profiles of catecholamine production compared with those of rat pheochromocytomas. Clonal cell lines were established from a representative tumor and were evaluated for responsiveness to agents known to affect the development and function of normal and neoplastic rat chromaffin cells.

RESULTS

Although adrenal medullary cells from normal rodents produce epinephrine before birth, polyoma-induced mouse adrenal tumor cells are immature or poorly differentiated. They synthesize norepinephrine, but not epinephrine, which during normal development is produced later than norepinephrine. They also produce relatively large quantities of dihydroxyphenylalanine, suggesting an abnormality of catecholamine biosynthesis such that tyrosine hydroxylase is not rate-limiting. Secretory granules are sparse, as demonstrated by electron microscopy or by staining for chromogranin A, and catecholamine stores are low. Further, the tumor cells appear to be phenotypically unstable, as judged from heterogeneous staining for tyrosine hydroxylase even in early passage, twice-cloned cell lines. Tumor cell morphology and catecholamine profiles appear to be unaffected or minimally affected by nerve growth factor, forskolin or dexamethasone, which are known to affect normal or neoplastic rat chromaffin cells. However, tumors formed after subcutaneous injection of cell lines into mice show up to a 10-fold increase in catecholamine stores, suggesting that the cells are subject to some forms of regulation. The cloned cell lines do not produce detectable polyoma virus, but express all three viral T antigens, including a characteristic, truncated form of large T.

CONCLUSIONS

The findings suggest that the process of neoplastic transformation and/or the presence of polyoma virus T antigens results in suppression of the adrenergic phenotype in mouse adrenal chromaffin cells. T antigens might therefore be useful as tools for studying mechanisms that regulate the differentiation and maturation of chromaffin cells in normal and neoplastic states. Furthermore, although polyoma virus cannot be readily used to produce adrenergic cell lines from the mouse adrenal medulla, the lines that are produced might substitute for PC12 cells in some types of studies that require a mouse model.

Neuroimmune modulation: signal transduction and catecholamines

In recent years, much interest has centered on the commonalities and bi-directional interactions between the nervous system and the immune system. This review focuses on mechanisms through which, catecholamines, a class of neuro-endocrine molecules, modulate immune functions. Catecholamines can be immune suppressive and inhibit lymphocyte activation of both T and B cells as well as the generation of immune-mediated anti-tumor responses. Some of these catecholamine-regulated activities appear to be modulated through the second messenger, cyclic AMP, whereas others appear to be catecholamine-dependent but cyclic AMP independent. Further delineation of the interacting ligand-receptor complexes, populations of responding cells and signal transduction mechanisms leading to the activation of specifically involved genes and gene products, will lead to enhanced understanding of the integratory functions of the nervous system in immune responses, the biology of stress, the role of stress-associated molecular mechanisms in perturbations of physiological homeostasis and the development of a new biological psychiatry with accompanying rational therapeutic modalities.

Nicotinic agonists, phorbol esters, and growth factors activate two extracellular signal-regulated kinases, ERK1 and ERK2, in bovine chromaffin cells

Treatment of bovine chromaffin cells with nicotinic agonists, phorbol esters, and growth factors increases protein kinase activity toward microtubule-associated protein-2 and myelin basic protein (MBP) in vitro. To characterize the kinases that are activated by these agents, we separated chromaffin cell proteins by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels into which MBP had been incorporated, allowed the proteins to renature, and then assayed MBP kinase activity by incubating the gels with [gamma-32P]ATP. Chromaffin cells contain a family of kinases that phosphorylate MBP in vitro. Two of these kinases, of M(r) 46,000 and 42,000 (PK46 and PK42), were activated by treatment of the cells with dimethylphenylpiperazinium (DMPP), phorbol 12,13-dibutyrate (PDBu), or insulin-like growth factor I (IGF-I). Activation of PK46 and PK42 by DMPP was dependent on extracellular Ca2+, whereas the effects of PDBu and IGF-I were Ca2+ independent. Down-regulation of protein kinase C by incubation of the cells with PDBu abolished the activation of PK46 and PK42 by DMPP, PDBu, and IGF-I. Staurosporine, a protein kinase C inhibitor, prevented the activation of PK46 and PK42 by DMPP and PDBu but did not block the activation of these kinases by IGF-I. Immunoblotting experiments with antiphosphotyrosine (anti-PTyr) antibodies demonstrated that agents that increased the kinase activities of PK46 and PK42 also increased the apparent PTyr content of M(r) 46,000 and 42,000 proteins. PK46 and PK42 comigrated with proteins that reacted with antibodies against extracellular signal-regulated kinases (ERKs). Thus, PK46 and PK42 appear to be the bovine homologues of ERK1 and ERK2.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute and chronic cycle length dependent increase in ventricular pacing threshold

Several factors have been shown to influence ventricular pacing threshold in humans, including pacing lead location (endocardial vs epicardial), lead maturation, and antiarrhythmic agents. To determine whether ventricular pacing rate has a significant influence on acute and chronic pacing thresholds, we measured pacing thresholds in 16 patients receiving an implantable antitachycardia pacemaker cardioverter defibrillator (Cadence). Ventricular pacing thresholds were determined using the device programmer at cycle lengths of 600, 400 and 300 msec at the time of implantation; prior to hospital discharge at 3-14 days; and during follow-up outpatient visits at 6-8 weeks, 3 months, and 6 months to 1 year. Eleven patients had an epicardial lead system and five an endocardial lead system. Eleven patients were being treated with antiarrhythmic drug therapy. Device output ranged from 1-10 V and was adjustable in 1-V increments (pulse width was held constant at 1 msec). A cycle length dependent increase in pacing threshold (defined as a > or = 1-V increase in threshold at 400 or 300 msec relative to 600 msec) was observed in 10/16 patients during 12/72 pacing trials at 400 msec, and in 15/16 patients during 31/67 trials at 300 msec. In trials in which an increase in pacing threshold occurred, the magnitude of the increase at 400 msec relative to 600 msec was only 1 V in all 12 trials, but at 300 msec the increase ranged from 4-9 V in 7/31 (23%) trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Voltage-dependent phosphorylation may recruit Ca2+ current facilitation in chromaffin cells

Bovine chromaffin cells have two components of whole-cell Ca2+ current: 'standard' Ca2+ currents that are activated by brief depolarizations, and 'facilitation' Ca2+ currents, which are normally quiescent but can be activated by large pre-depolarizations or by repetitive depolarizations to physiological potentials. The activation of protein kinase A can also stimulate Ca2+ current facilitation, indicating that phosphorylation can play a part in facilitation. Here we investigate the role of protein phosphorylation in the recruitment of facilitation Ca2+ currents by pre-pulses or repetitive depolarizations. We find that recruitment of facilitation by depolarization is a rapid first-order process which is suppressed by inhibitors of protein phosphorylation or by injection of phosphatase 2A into cells. Recruitment of facilitation Ca2+ current by voltage is normally reversible but phosphatase inhibitors render it irreversible. Our results indicate that recruitment of these Ca2+ currents by pre-pulses or repetitive depolarizations involves voltage-dependent phosphorylation of the facilitation Ca2+ channel or a closely associated regulatory protein. Voltage-dependent phosphorylation may therefore be a mechanism by which membrane potential can modulate ion channel activity.

Mouse hepatitis virus infection suppresses modulation of mouse spleen T-cell activation

Natural infection by mouse hepatitis virus (MHV) can affect interpretation of immunological studies in mice. MHV, a collective term describing a group of corona viruses, is found in natural infections in over 70% of laboratory mouse populations in the U.S.A. and Canada. Natural outbreaks of MHV in our animal colony afforded us the opportunity to study MHV-induced immunosuppression as well as the effects of MHV infection on neurotransmitter immunomodulation. Concanavalin A (Con A)-stimulated DNA synthesis by spleen T lymphocytes from MHV-infected mice was 20-50% that of non-infected mice. The MHV infection also altered neurotransmitter modulation of spleen T-lymphocyte activation. In contrast to noradrenaline ablation of Con A-activated DNA synthesis by spleen lymphocytes from non-infected mice, DNA synthesis by the infected group was not inhibited by noradrenaline or dibutyryl-cAMP. These effects of MHV infection were specific for spleen T lymphocytes since MHV infection did not alter Con A stimulation of thymocytes, lipopolysaccharide stimulation of spleen B lymphocytes, or noradrenaline inhibition of thymocyte and B-cell DNA synthesis. MHV infection also did not alter spleen T-lymphocyte subset proportions. Thus, MHV infection inhibits spleen T-lymphocyte activation and blocks in vitro catecholamine and cAMP regulation of spleen T-cell activation but does not affect activation of thymic cells or spleen B cells.

Phorbol esters cause preferential secretion of norepinephrine from bovine chromaffin cells

Differential secretion of norepinephrine and epinephrine was studied in cultured bovine chromaffin cells. Nicotinic agonists and 55 mM K+ evoked a slightly greater release of norepinephrine than of epinephrine: The percentage of norepinephrine secreted was 1.5 to two times greater than the percentage of epinephrine secreted. In contrast, when the cells were treated with phorbol 12,13-dibutyrate, the percentage of norepinephrine released was six to eight times greater than that of epinephrine released. Similar results were obtained in experiments with cultures highly enriched in either norepinephrine-containing cells or epinephrine-containing cells. In response to 55 mM K+, catecholamine release from norepinephrine-containing cells was two times greater than that from epinephrine-containing cells. In response to phorbol 12,13-dibutyrate, secretion from norepinephrine-containing cells was 13 times greater than that from epinephrine-containing cells. These results suggest that protein kinase C plays a specific role in the regulation of catecholamine secretion from norepinephrine-containing cells.

Omega-conotoxin GVIA blocks a Ca2+ current in bovine chromaffin cells that is not of the "classic" N type

Previous studies have identified two components of whole-cell Ca2+ current in bovine chromaffin cells. The "standard" component was activated by single depolarizations, while "facilitation" could be activated by large prepulses or repetitive depolarizations. Neither current component was sensitive to changes in holding potential between -100 and -50 mV; thus neither appeared to be carried by N-type Ca2+ channels. We now report that the facilitation Ca2+ current is insensitive to omega-conotoxin GVIA (omega-CgTx), but that the toxin blocks approximately 50% of the standard Ca2+ current. In some cells the toxin blocks all of the standard Ca2+ current, in others about half of the current, while in others it has no effect. Kinetic differences in current activation are observed after toxin application. These results suggest that the standard component of chromaffin cell Ca2+ current is composed of two pharmacologically distinct channels-one is omega-CgTx sensitive and the other is not. Two kinetically distinct types of 14 pS Ca2+ channels that may correspond to the omega-CgTx-sensitive and -insensitive components were observed in single-channel experiments. Because omega-CgTx blocked Ca2+ channels that were not inactivated by a depolarized holding potential, the commonly used Ca2+ channel categorization scheme may be inadequate to describe the Ca2+ channels found in chromaffin cells.

Activation of a microtubule-associated protein-2 kinase by insulin-like growth factor-I in bovine chromaffin cells

Treatment of bovine chromaffin cells with insulin-like growth factor-I (IGF-I) caused the activation of a protein kinase that phosphorylates microtubule-associated protein-2 (MAP-2) in vitro. Activation of MAP-2 kinase by IGF-I varied with the time of treatment (maximal at 10-15 min) and the concentration of IGF-I (maximal at 10 nM). The IGF-I-activated MAP-2 kinase was localized to the soluble fraction of chromaffin cell extracts and required Mg2+ for activity. The IGF-I-activated kinase also phosphorylated myelin basic protein, but had little or no activity toward histones or ribosomal S6 protein. To examine the role of protein tyrosine phosphorylation in the activation of the MAP-2 kinase, we isolated phosphotyrosine (PTyr)-containing proteins from chromaffin cells by immunoaffinity adsorption on anti-PTyr-Sepharose beads. Anti-PTyr-Sepharose eluates from IGF-I-treated cells showed increased MAP-2 kinase activity; thus, the MAP-2 kinase (or a closely associated protein) appears to be a PTyr-containing protein. Treatment of anti-PTyr-Sepharose eluates or crude chromaffin cell extracts with alkaline phosphatase significantly decreased kinase activity toward myelin basic protein, indicating that phosphorylation of the IGF-I-activated kinase is required for its activity.

Three types of bovine chromaffin cell Ca2+ channels: facilitation increases the opening probability of a 27 pS channel

1. Cell-attached patch recordings from bovine chromaffin cells were performed with 90 mM-Ba2+ in the patch pipette and with isotonic potassium aspartate in the bathing solution to zero the membrane potential. Three different types of unitary Ca2+ channel activity could be distinguished in these recordings. 2. A 27 pS Ca2+ channel was distinguished by constructing amplitude histograms and measuring slope conductance. This channel activated over a broad range of potentials (depolarizations greater than -10 mV). 3. A second Ca2+ channel with a slope conductance of 14 pS could also be detected with amplitude histograms. This channel activated with depolarizations greater than -20 mV. 4. An 18 pS Ca2+ channel was observed infrequently indicating that this channel may carry only a small amount of the whole-cell current. This 18 pS channel was sensitive to changes in holding potential. Depolarizing the patch to +10 mV from a holding potential of -80 mV elicited robust unitary activity. Changing the patch holding potential to -40 mV while maintaining test depolarizations to +10 mV completely inactivated the 18 pS channel. Neither the 25 pS nor the 14 pS Ca2+ channels were affected by changes in holding potential in the range from -80 mV to -40 mV, indicating the 18 pS channel was a different type of channel. As the 18 pS channel was observed so infrequently, no detailed studies of it were possible. 5. Chromaffin cell Ca2+ currents exhibited facilitation. Large pre-depolarizations greatly augmented whole-cell currents observed in these cells. Whole-cell currents could double or triple after recruiting facilitation. The application of large pre-depolarizations altered the gating behaviour of the 27 pS Ca2+ channel manifested as dramatically increased channel opening probabilities measured during subsequent test pulses. Large pre-depolarizations induced unitary activity in the 27 pS Ca2+ channel similar to the long-lived openings exhibited by L-type Ca2+ channels in the presence of Bay K 8644. Large pre-depolarizations did not change the gating behaviour of the 14 pS Ca2+ channel. 6. Repetitive depolarizations in the physiological range could also induce facilitation. At the single-channel level facilitation was manifested as a striking increase in opening probability of the 27 pS Ca2+ channel. No effect of repetitive activity was observed on 14 pS channel gating. At the whole-cell level, repetitive depolarizations dramatically increased the current observed. 7. Facilitation of 27 pS Ca2+ channel activity could be induced by changing the holding potential to a depolarized level (greater than or equal to -10 mV).(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factor-I enhances tyrosine hydroxylase activation in bovine chromaffin cells

Previous studies have shown that insulin-like growth factor-I (IGF-I) enhances secretagogue-stimulated Ca2+ uptake and catecholamine release in bovine chromaffin cells. This report describes the effect of IGF-I on the activity of tyrosine hydroxylase (tyrosine 3-monooxygenase, EC 1.14.16.2), the major regulatory enzyme in the pathway of catecholamine biosynthesis. Tyrosine hydroxylase activity was assayed by measuring 3,4-dihydroxyphenylalanine (Dopa) accumulation in the presence of brocresine, an inhibitor of Dopa decarboxylase. Chromaffin cells cultured in serum-free medium produced approximately 40% less Dopa when stimulated by 55 mM K+ than did cells that had been cultured in the presence of serum. Incubation of cells for 3 days in serum-free medium containing 10 nM IGF-I restored high K(+)-stimulated Dopa accumulation to a level comparable to that seen in cells cultured continuously in serum-containing medium. In eight experiments, IGF-I increased high K(+)-stimulated Dopa accumulation (expressed as picomoles per minute per milligram of protein) by 96 +/- 13%. IGF-I increased the protein content of chromaffin cells by approximately 30%; consequently, its effect on tyrosine hydroxylase activity was even greater when Dopa synthesis was expressed as picomoles per minute per 10(7) cells. IGF-I also enhanced the rate of Dopa accumulation in cells stimulated by dimethylphenylpiperazinium, 8-bromo-cyclic AMP, phorbol 12,13-dibutyrate, or Ba2+. The effect of IGF-I on high K(+)-stimulated tyrosine hydroxylase activity was measurable when enzyme activity was assayed in vitro, suggesting that this effect was due to a stable modification of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphotyrosine-containing proteins in bovine chromaffin cells: effects of insulin-like growth factor I (IGF-I)

1. Antiphosphotyrosine antibodies were used to detect phosphotyrosine-containing proteins in immunoblots of bovine chromaffin cell proteins. 2. Unstimulated cells exhibited two major phosphotyrosine-containing proteins, which had Mr's of 121,000 and 70,000. Insulin-like growth factor I (IGF-I) had little effect on the phosphotyrosine content of these two proteins but greatly increased the phosphotyrosine content of three other proteins of Mr 185,000, 170,000, and 96,000. These proteins were found predominantly in the particulate fraction of cell homogenates. 3. The effects of the IGF-I were time and concentration dependent, with maximal increases in phosphorylation occurring after 1 min of treatment with 10 nM IGF-I. Na3VO4, an inhibitor of phosphotyrosine phosphatases, potentiated the effects of IGF-I. 4. Thus, the IGF-I receptor appears to function as an IGF-I-activated protein tyrosine kinase in chromaffin cells. The tyrosine kinase activity of the IGF-I receptor presumably mediates the effects of IGF-I on chromaffin cell function.

Two types of Ca2+ currents are found in bovine chromaffin cells: facilitation is due to the recruitment of one type

1. Whole-cell Ca2+ currents in cultured bovine chromaffin cells were studied using patch-clamp electrophysiology. With Ba2+ or Ca2+ as the current carriers, two separate components of whole-cell current could be distinguished by biophysical and pharmacological criteria. These components of Ca2+ current were different from T- or N-type Ca2+ channels previously described, as they were not inactivated at a holding potential of -60 mV. 2. Depolarization of the cells past -20 mV in 10 mM-Ba2+ activated a single component of Ca2+ current, called the 'standard' current. This current showed no detectable voltage-dependent inactivation, but did show marked current-dependent inactivation as steady-state inactivation (H-infinity) plots obtained in the presence of Ba2+ were quite different from those obtained from Ca2+. 3. In most chromaffin cells large pre-depolarizations or repetitive depolarizations in the physiological range activated a second component of Ca2+ current called 'facilitation'. Facilitation was observed with either Ca2+ or Ba2+ as the charge carrier. Recruiting facilitation increased whole-cell currents by an average of 60%. 4. Pre-pulses to +120 mV lasting 200 ms completely activated facilitation. Pre-pulses longer than 800 ms started to inactivate facilitation, while pre-pulses longer than 2500 ms completely inactivated this component of Ca2+ current. Because only outward currents were recorded at +120 mV, it is likely that facilitation inactivated in a voltage-dependent manner. 5. When the extracellular Ba2+ concentration was increased in the range from 2 to 90 mM activation of both facilitation and standard Ca2+ currents shifted in the depolarizing direction. In 2 mM-Ba2+ facilitation activated at potentials 10 mV more negative than the standard component, while in 90 mM-Ba2+, facilitation activated at a potential about 10 mV more depolarized than the standard component. Thus, the voltage sensor for the facilitation Ca2+ current appeared to sense more surface charge than did the standard Ca2+ current. 6. Tail currents measured at -20 and -30 mV in the absence of facilitation (without pre-pulses) showed one time constant for current deactivation. Tail currents measured with both facilitation and standard currents activated showed a significantly slower deactivation rate than that seen with the standard current alone. 7. The dihydropyridine antagonist nisoldipine (1 microM) completely suppressed the facilitation Ca2+ current even when cells were held at negative holding potentials (-80 mV). In contrast, the standard current was unaffected by 1 microM-nisoldipine, even at depolarized holding potentials (-20 mV).(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of facilitation calcium channels in chromaffin cells by D1 dopamine receptors through a cAMP/protein kinase A-dependent mechanism

Facilitation calcium channels in unstimulated bovine chromaffin cells are normally quiescent but are activated by large pre-depolarizations or by repetitive depolarization in the physiological range. The activation of these 27-pS dihydropyridine-sensitive channels by repetitive stimulation, such as by increased splanchnic nerve activity, can lead to an almost twofold increase in Ca2+ current in these cells. This increase in Ca2+ current is of probable physiological importance in stimulating rapid catecholamine secretion in response to danger or stress. We have identified D1 dopaminergic receptors on bovine chromaffin cells by fluorescence microscopy. Here we show that stimulation of the D1 receptors activates the facilitation Ca2+ currents in the absence of pre-depolarizations or repetitive activity, and that activation by D1 agonists is mediated by cyclic AMP and protein kinase A. The recruitment of facilitation Ca2+ channels by dopamine may form the basis of a positive feedback loop mechanism for catecholamine secretion.

Mimicry and inhibition of nerve growth factor effects: interactions of staurosporine, forskolin, and K252a in PC12 cells and normal rat chromaffin cells in vitro

The structurally similar compounds staurosporine and K252a are potent inhibitors of protein kinases. K252a has previously been reported to inhibit most or all of the effects of nerve growth factor (NGF) on PC12 pheochromocytoma cells, and staurosporine has been reported both to inhibit and to mimic NGF-induced neurite outgrowth from a PC12 cell subclone in a dose-dependent manner. We have studied the interactions of these agents with each other, with NGF, and with forskolin, an activator of adenylate cyclase, on the parent PC12 cell line and on normal neonatal and adult rat chromaffin cells. Staurosporine alone or in conjunction with forskolin induces outgrowth of short neurites from PC12 cells but does not substitute for NGF in promoting cell survival. It does not abolish NGF-induced neurite outgrowth but does reverse the effects of NGF on catecholamine synthesis. K252a abolishes NGF-induced neurite outgrowth but only partially decreases outgrowth induced by NGF plus forskolin. It does not inhibit neurite outgrowth produced by staurosporine or staurosporine plus forskolin. These findings with PC12 cells suggest that staurosporine might act downstream from K252a and NGF on components of one or more signal transduction pathways by which NGF selectively affects the expression of certain traits. Both neonatal and adult rat chromaffin cells show dramatic flattening and extension of filopodia in response to staurosporine, an observation suggesting that some of the same pathways might remain active in cells that do not exhibit a typical NGF response. Only a small amount of neurite outgrowth is observed, however, and only in neonatal cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic localization of insulin-like growth factor I binding sites in the bovine adrenal gland and on cultured bovine adrenal chromaffin cells

Abstract Previous studies have reported the presence of binding sites for insulin-like growth factor I (IGF-I) in membranes prepared from isolated bovine adrenal medullary cells, and IGF-I was found to regulate the secretory function of bovine chromaffin cells. In the present study, binding sites for IGF-I have been localized in sections of bovine adrenal gland and on cultured bovine adrenal medullary cells, using [(125) l][Thr(59)]-IGF-l as the ligand in conjunction with qualitative autoradiographic techniques. Binding sites were present throughout the adrenal gland and were distributed evenly over all cortical cell layers and over both adrenaline and noradrenaline cell types in the medulla. They were also present at lower density over blood vessels and nerve bundles and over the capsule. The binding of radioligand was to a single class of sites with K(d) 0.61 nM, and was completely displaced by excess unlabelled [Thr(59)]-IGF-l and by insulin (Actrapid, K(d) 1.04muM). Binding sites were also identified on single cells in primary monolayer cultures of bovine adrenal medullary cells. More than 96% of the cells possessed binding sites, although only 85% of such cells were chromaffin cells, as previously determined from dopamine beta-hydroxylase immunohistochemical staining. The results suggest that IGF-I may affect the maturation, growth or function not only of adrenal chromaffin cells but also of many others cell types in this tissue.

Studies on the effect of insulin-like growth factor-I on catecholamine secretion from chromaffin cells

Chromaffin cells cultured in serum-free medium secreted a smaller percentage of their catecholamine stores in response to stimulation by high K+ (55 mM) than did cells cultured in serum-containing medium. Addition of insulin-like growth factor-I (IGF-I) to serum-free medium restored high K(+)-stimulated catecholamine secretion to the levels seen in serum-treated cultures. In contrast, addition of IGF-I to serum-containing medium had little effect on catecholamine secretion. These results suggest that serum contains IGF-I or another factor that maintains the secretory responsiveness of chromaffin cells. IGF-I not only enhanced high K(+)-stimulated catecholamine secretion, but also augmented secretion elicited by the nicotinic agonist dimethyl-phenylpiperazinium, the dihydropyridine agonist Bay K 8644, and Ba2+. IGF-I did not affect the dependence of catecholamine secretion on extracellular Ca2+ concentration nor did it affect the time course of secretion. Experiments using 45Ca2+ demonstrated that IGF-I treatment enhanced Ca2+ uptake into the cells. When cells were permeabilized by treatment with digitonin, Ca2(+)-dependent catecholamine secretion was slightly, but consistently, greater from IGF-I-treated cells than from untreated cells. Our results suggest that IGF-I may enhance catecholamine secretion partly by increasing Ca2+ entry into the cells and partly by affecting a step distal to Ca2+ entry.

Characterization of insulin-like growth factor-I receptors in PC12 pheochromocytoma cells and bovine adrenal medulla

Competitive binding studies indicated that PC12 cells have receptors for insulin-like growth factor-I (IGF-I). There are approximately 11,000 +/- 1,500 IGF-I receptors/cell; these receptors have an apparent KD for IGF-I of 7.2 +/- 0.6 nM. Covalent cross-linking of 125I-IGF-I to PC12 cells labeled a 125,000-130,000-Mr protein, presumably the alpha-subunit of the IGF-I receptor. Although PC12 cells also have insulin receptors, the 125I-IGF-I appeared to be cross-linked to IGF-I receptors, because 100 nM IGF-I competed for labeling but 100 nM insulin did not. Bovine chromaffin cells also have IGF-I receptors. The protein tyrosyl kinase activity of IGF-I receptors from bovine adrenal medulla and PC12 cells was examined after purification of the receptors by wheat germ agglutinin-Sepharose chromatography. IGF-I (10 nM) stimulated autophosphorylation of the beta-subunits of the IGF-I receptors from both preparations; the beta-subunits from both sources had Mr values of approximately 97,000. IGF-I also stimulated phosphorylation of the synthetic substrate poly(Glu:Tyr)4:1 by both receptor preparations. IGF-I (IC50 of approximately 0.2 nM) was much more potent than insulin at stimulating phosphorylation of poly(Glu:Tyr) by the bovine adrenal medulla preparation. A maximal concentration of IGF-I (10 nM) increased phosphorylation approximately threefold. IGF-I was slightly more effective than insulin at stimulating the phosphorylation of poly(Glu:Tyr) by the PC12 cell receptor preparation, but neither ligand produced a maximal effect at concentrations up to 100 nM. This result probably reflects the presence of comparable numbers of IGF-I and insulin receptors on PC12 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorylation of tyrosine hydroxylase in protein kinase C-deficient PC12 cells

In order to study the role of protein kinase C in the regulation of tyrosine hydroxylase phosphorylation in PC12 cells, the effects of various agonists on diacylglycerol accumulation in PC12 cells were measured and the ability of these agonists to increase the phosphorylation tyrosine hydroxylase in protein kinase C-deficient cells was evaluated. Bradykinin (10 microM) and elevated extracellular K+ (55 mM) increased the accumulation of [3H]diacylglycerol in PC12 cells that had been prelabeled with [3H]arachidonic acid, and so might be expected to activate protein kinase C in these cells; in contrast, nerve growth factor did not increase diacylglycerol accumulation in PC12 cells. Protein kinase C-deficient PC12 cells were prepared by incubating the cells for 24 h with 1 microM phorbol dibutyrate. This treatment resulted in the loss of approximately 90% of the protein kinase C activity in the cells. Control and protein kinase C-deficient cells were incubated with 32Pi for 90 min and then stimulated with various agonists. 32P-labeled tyrosine hydroxylase was isolated from the cells by polyacrylamide gel electrophoresis and subjected to tryptic hydrolysis. 32P-containing phosphopeptides were separated by two-dimensional thin-layer electrophoresis and chromatography, visualized by autoradiography, and quantitated by scintillation counting Treatment of control cells with phorbol dibutyrate increased the incorporation of 32P into one tryptic phosphopeptide (referred to as T3) in tyrosine hydroxylase. Phorbol dibutyrate did not increase the phosphorylation of this peptide in protein kinase C-deficient cells. Bradykinin or 55 mM K+ increased the incorporation of 32P into four tyrosine hydroxylase phosphopeptides, including peptide T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Bovine chromaffin cells have insulin-like growth factor-I (IGF-I) receptors: IGF-I enhances catecholamine secretion

The binding of 125I-insulin-like growth factor-I (125I-IGF-I) to bovine chromaffin cells was measured. Chromaffin cell cultures contained 111,000 +/- 40,000 IGF-I binding sites/cell. These sites bound IGF-I with a KD of 1.1 +/- 0.3 nM and had a much lower affinity for insulin. Cross-linking studies showed that 125I-IGF-I bound to a protein that had an Mr of approximately 125,000, similar to the Mr of the alpha subunit of the IGF-I receptor in other tissues. Cells cultured with IGF-I (10 nM) for 4 days exhibited an almost twofold increase in high K+-evoked catecholamine secretion. Insulin was much less potent than IGF-I in enhancing catecholamine secretion. These data indicate that binding of IGF-I to its receptors on chromaffin cells can modulate the function of these cells.

Insulin and insulin-like growth factors stimulate deoxyribonucleic acid synthesis in PC12 pheochromocytoma cells

The effects of insulin and insulin-like growth factors (IGFs) on the replication of PC12 pheochromocytoma cells were investigated. Incubation of PC12 cells for 2-3 days in low (0.3%) serum medium decreased [3H]thymidine incorporation into PC12 cell DNA to approximately 30% of that in control (15% serum) medium. Incubation of the cells in low serum medium also slowed the growth of the cultures and increased the percentage of cells in the G0/G1 phase of the cell cycle. Addition of insulin to cells in low serum medium increased [3H]thymidine incorporation into the cells, increased the number of cells in PC12 cultures, and decreased the percentage of cells in the G0/G1 phase of the cell cycle. IGF-I and IGF-II also increased [3H]thymidine incorporation into PC12 cells incubated in low serum medium. IGF-I (EC50, approximately 0.3 nM) was a more potent stimulus of [3H]thymidine incorporation than was insulin (EC50, approximately 3.5 nM). These data suggest that insulin and IGFs are growth factors for PC12 cells, and that the growth-promoting effects of these agents may be mediated by a type I IGF receptor on PC12 cells.

Phosphorylation of elongation factor 2 in the rat superior cervical ganglion

Elongation factor 2 (EF-2) and its associated kinase, Ca2+/calmodulin-dependent protein kinase III, have recently been identified as a major protein phosphorylation system in mammalian tissues. We have measured the phosphorylation of EF-2 in 32P-labeled superior cervical ganglia. Phosphorylation of EF-2 was increased by preganglionic stimulation or by treatment of the ganglion with dimethylphenylpiperazinium or veratridine. Increases in EF-2 phosphorylation presumably reflect the activation of Ca2+/calmodulin-dependent protein kinase III by nicotinic stimulation and depolarization. The phosphorylation of EF-2 may help to coordinate neuronal protein synthesis with neuronal activity.

Vasopressin stimulates the phosphorylation of an 83,000 Mr protein in the superior cervical ganglion

1. 32P-Labeled proteins from the superior cervical ganglion of the rat were separated by two-dimensional gel electrophoresis and visualized by autoradiography. 2. The most heavily labeled phosphoprotein in the ganglion had a relative molecular weight of 83,000 and a pI of 4.5. Phosphorylation of this protein was increased by phorbol 12,13-dibutyrate, an activator of the Ca2+/phospholipid-dependent protein kinase, protein kinase C. This protein appears to be similar or identical to a specific protein kinase C substrate that has been described in other tissues (Blackshear, P. J., et al., J. Biol. Chem. 261:1459-1469, 1986). 3. Phosphorylation of this protein was also increased by treatment of the ganglion with phospholipase C (Bacillus cereus) but was not increased by 8-bromo-cyclic AMP or by nicotinic agonists. Vasopressin increased the hydrolysis of inositol-containing phospholipids in the ganglion and also increased the labeling of the 83,000 Mr protein. Thus, vasopressin appears to activate protein kinase C in the ganglion. 4. Muscarine, which also increased phospholipid metabolism in the ganglion, did not increase the phosphorylation of the 83,000 Mr protein. Muscarine and vasopressin stimulate phospholipid metabolism in different structures within the ganglion (Horwitz, J., et al., J. Pharmacol. Exp. Ther. 237:312-317, 1986). Muscarine may increase phospholipid metabolism in structures that do not contain significant amounts of the 83,000 Mr protein.

Preganglionic stimulation increases the phosphorylation of tyrosine hydroxylase in the superior cervical ganglion by both cAMP-dependent and Ca2+-dependent protein kinases

Electrical stimulation of the preganglionic cervical sympathetic trunk increases the phosphorylation of tyrosine hydroxylase in the superior cervical ganglion of the rat by a nicotinic mechanism and by a noncholinergic mechanism. We have measured the incorporation of [32P]Pi into specific tryptic phosphopeptides in tyrosine hydroxylase in order to identify the protein kinases that phosphorylate this enzyme in electrically stimulated ganglia. 32P-labeled tyrosine hydroxylase was isolated from the ganglion by immunoprecipitation and polyacrylamide gel electrophoresis and was subjected to tryptic hydrolysis. Seven tryptic peptides were resolved from these hydrolysates by two-dimensional thin-layer electrophoresis and chromatography. Preganglionic stimulation (20 Hz, 5 min) increased the incorporation of 32P into four of these peptides. In the presence of cholinergic antagonists, however, electrical stimulation increased the labeling of only one phosphopeptide. From a comparison of the effects of preganglionic stimulation with the effects of agonists that activate specific protein kinases, we conclude that electrical stimulation increases the phosphorylation of tyrosine hydroxylase by both a cAMP-dependent protein kinase and a Ca2+/calmodulin-dependent protein kinase. The nicotinic component of preganglionic stimulation appears to be mediated by a Ca2+/calmodulin-dependent protein kinase, while the noncholinergic component appears to be mediated by cAMP-dependent protein kinase. Although protein kinase C can phosphorylate tyrosine hydroxylase, this kinase does not appear to participate in the stimulation-induced phosphorylation of tyrosine hydroxylase in the superior cervical ganglion.