Lipid Testing Trends Before and After Hospitalization for Myocardial Infarction Among Adults in the United States, 2008-2019

Background

Routine monitoring of low-density lipoprotein cholesterol (LDL-C) identifies patients who may benefit from modifying lipid-lowering therapies (LLT). However, the extent to which LDL-C testing is occurring in clinical practice is unclear, specifically among patients hospitalized for a myocardial infarction (MI).

Methods

Using US commercial claims data, we identified patients with an incident MI hospitalization between 01/01/2008-03/31/2019. LDL-C testing was assessed in the year before admission (pre-MI) and the year after discharge (post-MI). Changes in LDL-C testing were evaluated using a Poisson model fit to pre-MI rates and extrapolated to the post-MI period. We predicted LDL-C testing rates if no MI had occurred (ie, based on pre-MI trends) and estimated rate differences and ratios (contrasting observed vs predicted rates).

Results

Overall, 389,367 patients were hospitalized for their first MI during the study period. In the month following discharge, 9% received LDL-C testing, increasing to 27% at 3 months and 52% at 12 months. Mean rates (tests per 1000 patients per month) in the pre- and post-MI periods were 51.9 (95% CI: 51.7, 52.1) and 84.4 (95% CI: 84.1, 84.6), respectively. Over 12 months post-MI, observed rates were higher than predicted rates; the maximum rate difference was 66 tests per 1000 patients in month 2 (rate ratio 2.2), stabilizing at a difference of 15-20 (ratio 1.2-1.3) for months 6-12.

Conclusion

Although LDL-C testing increased following MI hospitalization, rates remained lower than recommended by clinical guidelines. This highlights a potential gap in care, where increased LDL-C testing after MI may provide opportunities for LLT modification and decrease risk of subsequent cardiovascular events.

Adherence to endocrine therapy including ovarian suppression: A large observational cohort study of US women with early breast cancer

BACKGROUND

Recent clinical trials support adding ovarian suppression (OS) to oral endocrine therapy (ET) for premenopausal women with early breast cancer. The adoption of OS among real-world populations and the impact of OS on ET adherence have not been evaluated.

METHODS

This study examined a retrospective, observational cohort of women under the age of 50 years with incident early breast cancer from 2001 to 2016. The IBM MarketScan Commercial insurance claims database was used to identify new users of ET with or without OS and to track discontinuation of or adherence to ET. In all, 21,948 women filled at least 1 prescription for ET within 12 months of their diagnosis after a washout period of 12 months with no prior claims. Patients who received an aromatase inhibitor without a synchronous OS drug were excluded.

RESULTS

Use of OS increased over time and reached 11.3% in 2016. In an unadjusted analysis, 40.2% of ET+OS users discontinued ET early, whereas 48.8% of tamoxifen-alone users did. In adjusted analyses, ET+OS users had a similar likelihood of discontinuing ET in comparison with tamoxifen-alone users (hazard ratio, 0.92; 95% confidence interval, 0.83-1.03). Approximately 30% of women had low adherence over the first year of use. The likelihood of high adherence was similar, regardless of OS exposure.

CONCLUSIONS

The use of OS among young, commercially insured patients with breast cancer increased over time in agreement with recent clinical trial results but remained relatively low. Nonadherence to ET was common, but the use of OS was not associated with lower adherence to ET in this observational, nonrandomized cohort. These findings may reassure oncologists that use of OS does not endanger ET adherence, although prospective studies are needed for confirmation.

Race and delays in breast cancer treatment across the care continuum in the Carolina Breast Cancer Study

BACKGROUND

After controlling for baseline disease factors, researchers have found that black women have worse breast cancer survival, and this suggests that treatment differences may contribute to poorer outcomes. Delays in initiating and completing treatment are one proposed mechanism.

METHODS

Phase 3 of the Carolina Breast Cancer Study involved a large, population-based cohort of women with incident breast cancer. For this analysis, we included black women (n = 1328) and white women (n = 1331) with stage I to III disease whose treatment included surgery with or without adjuvant therapies. A novel treatment pathway grouping was used to benchmark the treatment duration (surgery only, surgery plus chemotherapy, surgery plus radiation, or all 3). Models controlled for the treatment pathway, age, and tumor characteristics and for demographic factors related to health care access. Exploratory analyses of the association between delays and cancer recurrence were performed.

RESULTS

In fully adjusted analyses, blacks had 1.73 times higher odds of treatment initiation more than 60 days after their diagnosis in comparison with whites (odds ratio [OR], 1.73; 95% confidence interval [CI], 1.04-2.90). Black race was also associated with a longer treatment duration. Blacks were also more likely to be in the highest quartile of treatment duration (OR, 1.69; 95% CI, 1.41-2.02), even after adjustments for demographic and tumor characteristics (OR, 1.31; 95% CI, 1.04-1.64). A nonsignificant trend toward a higher recurrence risk was observed for patients with delayed initiation (hazard ratio, 1.44; 95% CI, 0.89-2.33) or the longest duration (hazard ratio, 1.17; 95% CI, 0.87-1.59).

CONCLUSIONS

Black women more often had delayed treatment initiation and a longer duration than whites receiving similar treatment. Interventions that target access barriers may be needed to improve timely delivery of care.

Comparison of Medicare Claims-based Proxy Measures of Poor Function and Associations With Treatment Receipt and Mortality in Older Colon Cancer Patients

BACKGROUND

Multiple claims-based proxy measures of poor function have been developed to address confounding in observational studies of drug effects in older adults. We evaluated agreement between these measures and their associations with treatment receipt and mortality in a cohort of older colon cancer patients.

METHODS

Medicare beneficiaries age 66+ diagnosed with stage II-III colon cancer were identified in the Surveillance, Epidemiology, and End Results-Medicare database (2004-2011). Poor function was operationalized by: (1) summing the total poor function indicators for each model; and (2) estimating predicted probabilities of poor function at diagnosis. Agreement was evaluated using Fleiss' κ and Spearman's correlation. Associations between proxy measures and: (1) laparoscopic versus open surgery; (2) chemotherapy versus none; (3) 5-fluorouracil (5FU)+oxaliplatin (FOLFOX) versus 5FU monotherapy; and (4) 1-year mortality were estimated using log-binomial regression, controlling for age, sex, stage, and comorbidity. Survival estimates were stratified by functional group, age, and comorbidity.

RESULTS

Among 29,687 eligible colon cancer patients, 67% were 75+ years and 45% had stage III disease. Concordance across the poor function indicator counts was moderate (κ: 0.64) and correlation of predicted probability measures varied (ρ: 0.21-0.74). Worse function was associated with lower chemotherapy and FOLFOX receipt, and higher 1-year mortality. Within age and comorbidity strata, poor function remained associated with mortality.

CONCLUSIONS

While agreement varied across the claims-based proxy measures, each demonstrated anticipated associations with treatment receipt and mortality independent of comorbidity. Claims-based comparative effectiveness studies in older populations should consider applying one of these models to improve confounding control.

Abstract PR11: Temporal patterns of breast cancer treatment initiation and completion among black and white women in the Carolina Breast Cancer Study

Black women suffer from a persistent disparity in breast cancer mortality after controlling for prognostic and sociodemographic factors, suggesting that differential receipt or efficacy of treatment may contribute to their poorer outcomes. Black women are more likely to experience delays in diagnostic workup and initiation of treatment, but it is not known whether i) timeliness of subsequent care is also impacted, and ii) racial disparities in time to treatment initiation and completion persist among black and white women with comparable clinical and sociodemographic characteristics.

The Carolina Breast Cancer Study Phase III is a large population-based cohort of North Carolina women newly diagnosed with breast cancer. This study was restricted to black and white women undergoing surgery for the treatment of nonmetastatic disease. We investigated mean differences in the distribution of time from diagnosis to earliest surgery, chemotherapy, or radiation treatment (treatment initiation) and once started, time to treatment completion (treatment duration) by race. Only treatment-oriented surgeries excluding biopsies were included in this analysis, and last or definitive surgery was defined as the final treatment-oriented surgery occurring prior to recurrence and within 18 months of diagnosis. Cumulative incidence curves were used to graphically examine the distributions of time to treatment initiation and treatment duration, and general linear models were used to estimate crude and adjusted mean differences in time to treatment initiation and duration between black and white women. We also conducted stratified analyses to examine racial disparities by age and stage at diagnosis, hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) positivity, treatment pathway (surgery only, surgery plus chemotherapy, surgery plus radiation, or all three modalities), marital status, education level, income, and insurance type.

A total of 1,328 black and 1,331 white women met study inclusion criteria. Overall, black women had an average of 3.68 additional days to treatment initiation and 34.26 days longer treatment duration than white women, for 37.94 days longer total treatment time (95% confidence interval (CI): 34.21-41.67). Adjustment for clinical and sociodemographic factors resulted in a greater estimated mean difference in time to initiate treatment (4.04 days, 95% CI: 3.08-5.00), while it attenuated the mean difference in treatment duration towards the null (9.07 days, 95% CI: 6.82-11.32).

Black women experienced significantly longer time to initiate treatment and treatment duration in nearly every stratum of clinical or sociodemographic factor examined. Black women with stage II or III tumors had significantly longer time to initiate treatment than white women (4.50 and 7.84 days, respectively), and after starting treatment, treatment duration was approximately 25 days longer for black women with stage I and II disease. Black women undergoing radiation and/or chemotherapy had longer time to initiate treatment and significantly longer treatment durations. Having a college education or higher or being insured through Medicaid were associated with the greatest mean differences in time to treatment initiation comparing black and white women. Younger age at diagnosis, HR+ or HER2- disease, being unmarried, having less than a high school education, and being uninsured were associated with the greatest mean differences in treatment duration by race.

Overall, black women experienced longer intervals between diagnosis and treatment initiation and greater treatment durations after controlling for clinical and sociodemographic factors. Racial disparities were more pronounced in examination of treatment duration, suggesting that interventions to improve care coordination and timeliness should be targeted at high-risk groups.

Citation Format: Sophie E. Mayer, Melissa Troester, Stephanie B. Wheeler, Andrew Olshan, Lisa A. Carey, Jessica Tse, Katherine E. Reeder-Hayes. Temporal patterns of breast cancer treatment initiation and completion among black and white women in the Carolina Breast Cancer Study [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr PR11.

Abstract P4-10-01: Race, place and delays in breast cancer treatment across the care continuum in the Carolina breast cancer study

Black women have a persistent disparity in breast cancer survival after controlling for clinical factors, suggesting that differential receipt or efficacy of treatment may contribute to poorer outcomes. Delays in initiating treatment and subsequent spillover effects into time to completion are one proposed mechanism by which these survival disparities may occur.

The Carolina Breast Cancer Study Phase III is a large population-based study of North Carolina women with incident breast cancer. For this analysis, we included black (n=1328) and white (n=1331) women with stage I-III disease whose treatment included surgery with or without adjuvant therapies. Patients were grouped by treatment pathway (surgery only, surgery + chemotherapy, surgery + radiation, or all three modalities). We investigated the association of race with delays in treatment initiation, duration and completion. Delays in initiation of first treatment were modeled in two ways: i) time to initiation >30 days from diagnosis, and ii) time to initiation above the 75th percentile. Extended duration and delay in completion were defined as being > 75th percentile in days between initiation and end of treatment (duration) or days from diagnosis to end of treatment (completion) compared to others in the same pathway. Models controlled for treatment pathway, age, and tumor characteristics. Additional models controlled for demographic factors (marital status, income, education, insurance) and county-level factors related to care access (% urban and health professional shortage area status).

In analyses adjusted only for age at diagnosis, black women had a significantly higher risk of treatment delays whether measured by delay>30 days (risk ratio (RR) 1.24, 95% CI 1.12-1.37) and or by highest quartile of time to initiation (RR 1.23, 95% CI 1.07-1.40) compared to whites. They were also at higher risk of extended treatment duration (RR 1.47, 95% CI 1.29-1.69) and time to completion (RR 1.58, 95% CI 1.37-1.81) compared to others in the same pathway. Interestingly, adjustment for tumor characteristics did not impact effect estimates. While adjustment for demographic factors had little impact on the association of race with delays in initiation, it attenuated the association of race with delays in treatment duration and completion. Further adjustment for care access factors slightly attenuated the association of race with treatment initiation and completion, but did not impact associations with treatment duration. Significant racial disparities remained in delay across all phases of care after adjustment for clinical, demographic and access factors.

Overall, black women were at higher risk of delays in treatment initiation, extended duration and time to completion than white women receiving similar treatment, and these disparities appear to be compounded over the care continuum. These findings suggest that racial differences in income, education and insurance may partly explain observed disparities in treatment duration and time to completion, whereas care access factors may have more impact on disparities in treatment initiation, and interventions that target both patient-level and care access barriers may be needed to improve timely delivery across the care continuum.

Citation Format: Reeder-Hayes KE, Mayer SE, Olshan A, Carey LA, Wheeler SB, Tse C-K, Troester M. Race, place and delays in breast cancer treatment across the care continuum in the Carolina breast cancer study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-10-01.

Growing up in poor neighborhoods: how much does it matter?

This article is a review of research on how much the life chances of children are affected by the socioeconomic and racial mix of their schools and neighborhoods. The social mix of a high school has little effect on students' chances of attending college or on white students' academic achievement. Evidence about the effect of the socioeconomic mix of schools or neighborhoods on achievement of elementary school students, on graduation rates of high school students, on teenage crime, and on early labor market experience is weak. Growing up in poor neighborhoods seems to increase black teenage pregnancy rates.

5-Hydroxytryptamine type 2A and 2C receptors linked to Na+/K+/Cl- cotransport

The goal of the present paper was to investigate 5-hydroxytryptamine (5HT)2A and 5HT2C receptor regulation of ion transport in fibroblast cell lines transfected with these receptors. Na+/K(+)-ATPase and Na+/K+/2Cl- cotransport were measured with 86Rb+ as a surrogate for K+ uptake. Serotonin agonists had no effect on Na+/K(+)-ATPase activity in either cell line. Bumetanide, an antagonist of Na+/K+/2Cl- cotransport, almost completely blocked ouabain-insensitive K+ uptake in both cell lines, with an IC50 of about 1 microM. 36Cl- uptake was 2-fold greater than 86Rb+ uptake, consistent with the expected 2:1 stoichiometry. In addition, the Cl-/HCO3- uptake blocker 4,4'-diisothiostilbene-2,2'-disulfonic acid had no effect on Cl- uptake. The 5HT2A/2C receptor agonist (-)-2,5-dimethoxy-4-bromoamphetamine increased ouabain-insensitive K+ uptake, and this effect was blocked by bumetanide. The receptor antagonists mianserin and mesulergine, but not spiperone, blocked (-)-2,5-dimethoxy-4-bromoamphetamine responses in fibroblasts transfected with 5HT2C receptors, and all three antagonists blocked the effects in cells expressing 5HT2A receptors. Ouabain-insensitive 22Na+ uptake was similarly affected. 5HT receptor-related actions were not observed in untransfected parent NIH/3T3 fibroblasts. Thus, we have demonstrated that 5HT2C and 5HT2A receptors are linked to activation of Na+/K+/2Cl- cotransport in transfected fibroblasts. This activity may be a factor in the pharmacological actions of 5HT agonists and antagonists.

Sodium-dependent antiporters in choroid plexus epithelial cultures from rabbit

The mechanism of recovery from an acid load in primary cultures of rabbit choroid plexus epithelium (CPE) was examined, with emphasis on Na(+)-dependent antiports. Cells were incubated in saline solutions buffered to pH 7.38 with either HEPES or HCO3- plus 95% O2/5% CO2. Intracellular pH (pHi) was determined from the steady-state distribution of [14C]benzoate. Recovery after acidification with NH4Cl was rapid (t1/2 = 5 min) and was dependent on external Na+ (EC50 = 12 mM). Hexamethyleneamiloride and ethylisopropylamiloride, potent inhibitors of the Na+/H+ antiport, blocked 80% of recovery when [Na+] was 5 mM with IC50 values of 100 nM. However, neither drug blocked recovery in normal [Na+]. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of Cl-/HCO3- antiports, blocked recovery of pHi in a dose-related fashion in the presence of bicarbonate, but not in the presence of HEPES. No inhibition occurred with benzamil, an amiloride congener with high affinity for the Na+ channel, nor with dimethylbenzamil, an inhibitor of Na+/Ca2+ exchange. The carbonic anhydrase inhibitor acetazolamide also did not alter recovery from acidification. In CPE that had been pH-clamped with nigericin and KCl, the initial rate of 22Na+ uptake was very rapid (227 pmol/micrograms of DNA/min at pH 6.2), was dependent on external [Na+] with an EC50 value of 8 mM, and was inversely related to the pH of the medium. The maximal inhibition of 22Na+ uptake by hexamethyleneamiloride was 60% with an IC50 value of 76 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of hormone-sensitive adenylate cyclase in rabbit gallbladder mucosa

1. We have developed a plasma membrane preparation from the mucosal epithelium of rabbit gallbladder and have characterized the hormonal sensitivity of adenylate cyclase in this preparation. 2. Basal activity is low and is stimulated by GTP and GppNHp. Hormonal stimulation is largely dependent on exogenous guanine nucleotide. 3. Several prostaglandins (E1 approximately E2 greater than A1 greater than B1), vasoactive intestinal peptide and the beta-adrenergic agonist, isoproterenol, stimulate mucosal adenylate cyclase activity; a variety of peptides and neurotransmitters (secretin, cholecystokinin, arg-vasopressin, oxytocin, histamine, dopamine and serotonin) are without effect. 4. The data support the hypothesis that the inhibitory effect of prostaglandins, vasoactive intestinal peptide, and isoproterenol on gallbladder fluid absorption in certain species may be mediated by cyclic AMP. 5. The membrane preparation should be useful in further characterizing hormone receptor-transducer interactions of the gallbladder mucosal epithelium.

Methacholine sensitivity and cAMP protein kinase in tracheal smooth muscle

We studied regional variation in canine trachealis smooth muscle sensitivity and responsiveness to methacholine as well as basal and methacholine-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) and cAMP-dependent protein kinase activity. The trachea between the cricoid cartilage and the carina was divided into three segments of equal length (designated cervical, middle, and thoracic regions), each consisting of approximately 12-14 cartilage rings. Smooth muscle strips from each of the three regions were exposed to cumulative half-log increments of methacholine chloride. The sensitivity (-log EC50) and responsiveness (force per cross-sectional area and force per milligram protein) of the smooth muscle to methacholine in each region was determined from these data. Smooth muscle strips from cervical and thoracic regions were frozen before and after exposure to cumulative half-log increments of methacholine up to each region's previously determined EC50. Frozen samples were assayed for cAMP content or cAMP-dependent protein kinase activity. The relationship between resting tension and methacholine sensitivity and responsiveness were studied. For the size strips we used, 4 g resting tension set the average cervical and thoracic strips at 96 and 101% of their optimal length, respectively. The methacholine EC50 was not affected by a variation in resting tension. Sensitivity to methacholine was 7.1, 6.8, and 6.5 for cervical, middle, and thoracic regions, respectively. The responsiveness of the cervical and thoracic smooth muscle to methacholine was 16.4 and 16.3 g force/mm2, respectively, at an EC50 methacholine. Basal cAMP was lower in cervical smooth muscle than in thoracic. cAMP-dependent protein kinase activity ratios under both basal and EC50 methacholine-stimulated conditions were lower in cervical smooth muscle than in thoracic. We have observed in trachealis smooth muscle an inverse relationship between methacholine sensitivity and either cAMP or cAMP-dependent protein kinase activity. We suggest that cAMP and cAMP-dependent protein kinase play a role in the regulation of airway smooth muscle sensitivity to cholinergic agonists.

Inhibitory effect of methacholine on drug-induced relaxation, cyclic AMP accumulation, and cyclic AMP-dependent protein kinase activation in canine tracheal smooth muscle

Functional antagonism between bronchoconstricting and bronchodilating pathways was examined in canine tracheal smooth muscle. Trachealis strips were contracted with either 0.3 microM (EC55) or 3.0 microM (EC80) methacholine before being relaxed by the cumulative addition of isoproterenol, prostaglandin E2, or forskolin. The EC50 for all three relaxants was increased 10-fold in tissues contracted with 3.0 microM methacholine vs. those contracted with 0.3 microM methacholine. Moreover, contracting tissues with the higher concentration of methacholine reduced the maximum relaxation induced by prostaglandin E2 and isoproterenol. Forskolin produced total relaxation regardless of the concentration of methacholine used and thus was a much more effective bronchodilator than either isoproterenol or prostaglandin E2. The inhibitory effect of methacholine on the relaxant response to these agents was paralleled by a reduction in drug-stimulated cyclic AMP-dependent protein kinase activity. Methacholine reduced the maximum activation of cyclic AMP-dependent protein kinase elicited by isoproterenol, prostaglandin E2 and submaximal concentrations of forskolin, which was a much more powerful enzyme activator than the other two agents. The ability of a maximum concentration of forskolin (30 microM) to activate cyclic AMP-dependent protein kinase was not inhibited by methacholine. Although methacholine also appeared to suppress drug-stimulated cyclic AMP accumulation, the inhibitory effect was only statistically significant in forskolin-treated tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic GMP-dependent protein kinase activation in canine tracheal smooth muscle by methacholine and sodium nitroprusside

Methacholine (3 microM) and sodium nitroprusside (300 microM) increased cGMP-dependent protein kinase activity ratios (activity without cGMP divided by activity with 2 microM cGMP) in canine tracheal smooth muscle from a control value of 0.47 to 0.55 and 0.71, respectively. This correlates with 3-fold and 6-fold increases in cGMP concentrations in response to methacholine and sodium nitroprusside, respectively. Addition of charcoal to the homogenizing buffer prior to homogenization had no significant effect on the cGMP-dependent protein kinase response to either agent, suggesting that activation of the enzyme was not occurring as a result of cGMP release during homogenization. In order to limit cGMP dissociation from cGMP-dependent protein kinase during the assay procedure, it was necessary to perform assays at a reduced temperature (0 degree C) and with an abbreviated incubation time (2.5 min). When assayed at 30 degrees C, activated cGMP-dependent protein kinase rapidly lost activity. This inactivation occurred whether the enzyme had been activated exogenously, by exposing a supernatant fraction of canine trachealis to 0.1 microM cGMP, or endogenously, by treating intact canine trachealis with methacholine or sodium nitroprusside. By assaying instead at 0 degree C, the inactivation of cGMP-dependent protein kinase was minimized. Therefore, the activity ratio obtained by this new modified assay provided an estimate of the endogenous activation state of cGMP-dependent protein kinase. The data indicate that cGMP responses in canine trachealis to both methacholine and sodium nitroprusside are functionally linked to activation of cGMP-dependent protein kinase and are consistent with the hypothesis that cGMP, via cGMP-dependent protein kinase activation, regulates smooth muscle contractility.

Effects of adrenalectomy on activation of glycogen phosphorylase in rat myocardium

Adrenalectomy causes a depressed glycogenolytic response to catecholamines in myocardium. Total phosphorylase activity (a + b) is 20% lower in isolated, perfused hearts from adrenalectomized (ADX) rats compared with hearts from sham-operated (sham) rats even though the basal activity ratios (-AMP/+AMP) do not differ. In response to epinephrine (50 nM), the sham group has a higher activity ratio than the ADX group (0.23 vs. 0.16); the difference in specific activities of phosphorylase a in the two groups is even greater, 87 versus 49 U/mg protein. The glycogen content of the heart is 30% lower in the ADX group. Adrenalectomy does not alter the accumulation of cAMP and activation of cAMP-dependent protein kinase caused by epinephrine. Although rat heart contains a heat-stable phosphatase inhibitor, the activity of this inhibitor, as judged by phosphorylase phosphatase activity, is not altered by epinephrine stimulation or by adrenalectomy. Epinephrine perfusion increases the activity ratios (pH 6.8:8.2) of phosphorylase kinase equally in sham and ADX hearts; however, the specific activities of phosphorylase kinase (basal and hormone-stimulated) at either pH are lower after adrenalectomy. The sensitivity of phosphorylase kinase activity to stimulation by calcium is the same in the sham and ADX groups. A radioimmunoassay for phosphorylase kinase detects 10% less of this enzyme in hearts from adrenalectomized animals. Specific activities at pH 6.8 and 8.2 based on the quantity of phosphorylase kinase detected by radioimmunoassay suggest a lower phosphorylation state in the ADX group. Decreases in quantities of phosphorylase and phosphorylase kinase and enzyme dissociation due to glycogen depletion could all contribute to a depressed glycogenolytic response in the ADX group.

Functional antagonism in canine tracheal smooth muscle: inhibition by methacholine of the mechanical and biochemical responses to isoproterenol

The biochemical basis for the functional interaction between bronchoconstricting and bronchodilating pathways was investigated. Contracting canine trachealis strips with increasing concentrations of methacholine resulted in a progressive shift to the right of isoproterenol concentration-response curves. Thus, the EC50 for the relaxant response to isoproterenol was nearly 500-fold higher in preparations exposed to 3.0 microM methacholine than in tissues exposed to 0.03 microM methacholine. The maximum relaxation produced by isoproterenol was also dependent upon the initial muscarinic cholinergic tone. For example, isoproterenol reversed completely the contraction induced by 0.03 microM methacholine but did not relax trachealis strips contracted with 30 microM methacholine. To identify the molecular mechanism responsible for this functional antagonism, experiments were conducted to determine the effect of methacholine on isoproterenol-stimulated cyclic AMP accumulation and cyclic AMP-dependent protein kinase activation. Methacholine did not alter basal cyclic AMP content but did reduce cyclic AMP accumulation in response to isoproterenol. Furthermore, the ability of isoproterenol to activate cyclic AMP-dependent protein kinase was inhibited by methacholine in a concentration-dependent manner. This inhibition paralleled the decrease in mechanical responsiveness to isoproterenol. These results suggest that muscarinic cholinergic stimulation of canine tracheal smooth muscle functionally antagonizes the relaxant responses to beta adrenergic agonists and that a portion of this antagonism may be due to a suppression of catecholamine-stimulated cyclic AMP accumulation and cyclic AMP-dependent protein kinase activation.

Cyclic nucleotide-dependent protein kinases in airway smooth muscle

Because of the potential importance of cyclic nucleotide-dependent protein kinases in the regulation of airway smooth muscle tone, we have examined some of the characteristics of these enzymes in the soluble fraction of canine trachealis homogenates. In the absence of added cAMP, the heat-stable cAMP-dependent protein kinase inhibitor (PKI) abolished only a half of the 32P incorporation into mixed histones. The remaining activity appeared to be contributed by a cyclic nucleotide-independent enzyme. Phosphotransferase activity was enhanced 5-fold by 5 microM cAMP but only 70% of the cAMP-stimulated activity could be inhibited by PKI. The sensitivity of the cyclic nucleotide-dependent, PKI-resistant enzyme to cAMP, cGMP, and Mg2+ indicated that it was cGMP-dependent protein kinase. Because of the large amount of cyclic nucleotide-independent activity, and the ability of cAMP to activate cGMP-dependent protein kinase, the traditional "-cAMP/+cAMP" ratio did not provide an accurate assessment of the in vivo activation state of cAMP-dependent protein kinase. However, a modified assay was developed which allowed the precise measurement of cAMP-dependent, cGMP-dependent, and cyclic nucleotide-independent protein kinase activities. Using this new method, the cAMP-dependent protein kinase activity ratio of 0.239 in untreated trachealis strips was increased to 0.355 and 0.386 by prior exposure of the intact tissue to the smooth muscle relaxants isoproterenol and prostaglandin E2, respectively. The results of this study are consistent with the proposed role of cAMP-dependent protein kinase in the regulation of smooth muscle contractile function.

Isoproterenol-induced restoration of contraction in K+-depolarized hearts: relationship to cAMP

The action of isoproterenol on inotropic state, cAMP concentration, and phosphorylase b-to-a conversion was studied under conditions that are known to alter membrane properties in guinea pig papillary muscles. In accord with the results of other investigators, contractile events induced by electrical stimulation were abolished by tetrodotoxin (10 microM) or 22 mM K+ and were subsequently restored by the addition of isoproterenol (10 nM-100 microM). However, in the presence of 22 mM K+, but not tetrodotoxin, the dose-response and temporal relationships between isoproterenol and elevations in cAMP concentration were shifted to the right, whereas those for phosphorylase activation were shifted to the left. Thus the low concentrations (less than 10 nM) of isoproterenol that restored tension development did not produce a measurable increase in cAMP. Contractile responses induced by 10 nM isoproterenol were blocked by (--)-propranolol but not by (+)-propranolol or phentolamine. Methoxamine did not restore contractile events in 22 mM K+-treated muscles or induce changes in cAMP content or phosphorylase activation. These results show that conditions can be obtained (e.g., partial depolarization of cardiac cell membranes) in which beta-adrenergic receptor activation leads to restoration of inotropic state in guinea pig myocardium without an obligatory increase in tissue cAMP content. The restoration of contractile events and enhancement of phosphorylase response under these conditions suggest that beta-adrenergic receptor activation may lead to Ca2+-channel activation directly or by increasing a small pool of cAMP and thereby altering localized protein phosphorylation in the cell membrane.

Regulation of guinea pig heart phosphorylase kinase by cAMP, protein kinase, and calcium

In skeletal muscle the activation of phosphorylase kinase (PK) associated with phosphorylation of the enzyme can be measured as an increase in the pH 6.8:8.2 activity ratio. Phosphorylation leads to a 20- to 30-fold increase in PK activity (PKA) at pH 6.8 and a large decrease in the Km for phosphorylase. Perfused guinea pig hearts exposed to isoproterenol (0.3 microM) showed an increase in PKA, but without an increase in the pH 6.8:8.2 activity ratio. In a 10-fold dilution of guinea pig heart cytosol exposed to cAMP + methylisobutylxanthine, PKA was stimulated twofold at pH 7.5. Addition of exogenous protein kinase stimulated PKA fourfold. Both methods of activation were reversible and were blocked by the heat-stable inhibitor of protein kinase. Guinea pig heart PK was Ca2+-dependent requiring 0.6 microM Ca2+ for half-maximal activity. Kinetic studies indicate that the Km of guinea pig heart PK for phosphorylase b at pH 6.8 is not markedly reduced after in vitro activation (35%). This could explain the observed lack of increase in the pH 6.8:8.2 activity ratio after exposure of hearts to isoproterenol. The time course for the activation of inotropic state and the glycogenolytic pathway in perfused guinea pig hearts by isoproterenol showed that these processes were maximally activated within 25 s. However, PK remained activated for 2 min, long after the other biochemical and physiological parameters had returned to control values. These data suggest that Ca2+, not phosphorylation state, is important in regulating the return of dP/dt to control levels after beta-adrenergic stimulation.

Effects of ischemia on tissue metabolites in red (slow) and white (fast) skeletal muscle of the chicken

Brief periods of ischemia have been shown to produce marked reactive hyperemia in both red (slow) and white (fast) skeletal muscle. However, evidence is lacking for specific vasodilator metabolites which are rapidly produced in ischemic skeletal muscle. The present study examined the effects of 1 and 3 minutes of ischemia on creatine phosphate (CrP), adenine nucleotide metabolism, and anaerobic glycolysis in red anterior (ALD) and white posterior latissimus dorsi (PLD) muscles of the chicken. Tissue metabolite concentrations were determined from perchloric acid or trichloroacetic acid extracts using enzymatic assay or high pressure liquid chromatography. CrP or adenine nucleotides were not significantly altered in either muscle following 1 or 3 minutes of ischemia. However, adenosine increased by 611% in the ALD at 1 minute. Following 3 minutes of ischemia, adenosine concentrations were elevated by 439% and 201% in the ALD and PLD, respectively. The PLD showed the greatest increases in inosine and IMP. Inorganic phosphate increased by 67% and lactate increased by 142% in the ALD at 3 minutes. The PLD, which is reported to have a high anaerobic glycolytic capacity, showed no increase in lactate. These results support the hypothesis that adenosine may be a mediator of akeletal muscle reactive hyperemia following short periods of ischemia.

Adaptations of glycogen metabolism in rat epididymal adipose tissue during fasting and refeeding

It is well documented that adipose tissue glycogen content decreases during fasting and increases above control during refeeding. We now present evidence that these fluctuations result from adaptations intrinsic to adipose tissue glycogen metabolism that persist in vitro: in response to insulin (1 milliunit/ml), [3H]glucose incorporation into rat fat pad glycogen was reduced to 10% of control after a 3-day fast; incorporation increased 6-fold over fed control on the 4th day of refeeding following a 3-day fast. We have characterized this adaptation with regard to alterations in glycogen synthase and phosphorylase activity. In addition, we found that incubation of fat pads from fasted rats with insulin (1 milliunit/ml) increased glucose-6-P content, indicating that glucose transport was not the rate-limiting step for glucose incorporation into glycogen in the presence of insulin. In contrast, feeding a fat-free diet resulted in dramatic increases in glycogen content of fat pads without a concomitant increase in glucose incorporation into glycogen in response to insulin (1 milliunit/ml). Thus, fasting and refeeding appeared to alter insulin action on adipose tissue glycogen metabolism more than this dietary manipulation.

Interconversion between multiple glucose 6-phosphate-dependent forms of glycogen synthase in intact adipose tissue

We have tested the hypothesis that interconversion between multiple glucose-6-P-dependent forms of glycogen synthase helps regulate glycogen synthesis in adipose tissue. Our results indicate that interconversion of glycogen synthase in adipose tissue involves primarily dependent forms and that these interconversions were measured better by monitoring the activation constant (A0.5) for glucose-6-P than measuring the -: + glucose-6-P activity ratio. Insulin decreased and epinephrine increased the A0.5 for glucose-6-P without significant change in the activity ratio. Insulin consistently decreased the A0.5 in either the presence or absence of glucose, indicating that the insulin-promoted interconversion did not require increased hexose transport. Isoproterenol increased the A0.5 for glucose-6-P, while methoxamine was without effect, indicating beta receptors mediate adrenergic control of interconversion between glucose-6-P-dependent forms. The changes in the A0.5 produced by incubations with insulin or epinephrine were mutually reversible. We conclude that 1) glycogen synthesis in adipose tissue is catalyzed by multiple glucose-6-P-dependent forms of glycogen synthase, 2) hormones regulate glycogen metabolism by promoting reversible interconversions between these forms, and 3) there is no evidence that a glucose-6-P-independent form of glycogen synthase exists in intact adipose tissue.

Hormonally specific expression of cardiac protein kinase activity

The relationship between the effects of isoproterenol and prostaglandin E(1) (PGE(1)) on contractile state, cyclic AMP accumulation, and the activation states of protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37), phosphorylase kinase, glycogen synthase, and glycogen phosphorylase have been studied in the isolated perfused rat heart. Perfusion of hearts with isoproterenol (10 or 80 nM) caused enhancement of left ventricular dP/dt (P, pressure), increased intracellular cyclic AMP, increased the activation states of protein kinase, phosphorylase kinase, glycogen phosphorylase, and conversion of glycogen synthase to a less active form. PGE(1) (2 or 30 muM) increased cyclic AMP accumulation and activated protein kinase, but caused no detectable changes in dP/dt or the activation states of the protein kinase substrates involved in glycogen metabolism. Perfusion of hearts with either 10 nM isoproterenol or 30 muM PGE(1) produced comparable increases in cyclic AMP accumulation and protein kinase activity. Exposure of hearts to a combination of these agents caused additive effects on cyclic AMP content and protein kinase activity. However, values for phosphorylase kinase, glycogen phosphorylase, glycogen synthase, and dP/dt did not differ from those observed in the presence of 10 nM isoproterenol alone. The failure of PGE(1) to stimulate phosphorylation of protein kinase substrates was not due to an increase in phosphorylase phosphatase activity. We conclude that an increase in intracellular cyclic AMP and the subsequent activation of protein kinase are insufficient to change either the activities of phosphorylase kinase, glycogen phosphorylase, and glycogen synthase or the inotropic state of heart muscle.

Depressed cyclic AMP levels in airways smooth muscle from asthmatic dogs

We tested mongrel dogs by intradermal injection and tracheobronchial aerosol challenge with Ascaris suum antigen extract. All dogs were skin-test positive but could be segregated, on the basis of airways resistance measurements, into "asthmatic" (bronchoreactive) and "nonasthmatic" (nonbronchoreactive) groups. By using tracheal rings from these dogs, we measured the abilities of the beta-adrenergic agonist, isoproterenol, to relax tracheal smooth muscle contracted by methacholine and to cause cyclic AMP (cAMP) accumulation in the presence and absence of methacholine. The magnitude of relaxation induced by any concentration of isoproterenol was always less in the smooth muscle from "asthmatic" dogs. In the same tissues the concentrations of cAMP after in vitro equilibration, but prior to isoproterenol addition, were significantly less in the "asthmatic" than "nonasthmatic" samples. The accumulation of cAMP due to isoproterenol was similar in both groups for every dose of isoproterenol so that the initial difference between groups in cAMP concentration was maintained in an additive fashion over the entire dose-response curve. Total protein content of trachealis muscles from both groups of dogs was the same. We conclude that beta-adrenergically sensitive adenylate cyclase is not impaired in tracheal smooth muscle from "asthmatic" dogs; rather, the basal concentration of cAMP is depressed in "asthmatic" airway smooth muscle, and this difference is maintained throughout the isoproterenol dose-response curve. The depressed intracellular cAMP concentrations may be related to the decreased relaxation induced by isoproterenol in the "asthmatic" tracheal smooth muscle.

Electrophysiological responses of cardiac muscle to isoproterenol covalently linked to glass beads

We investigated the effects of isoproterenol aryl glass beads on the electrical properties of cardiac muscle and related these to our previous results concerning biochemical and contractile effects (Ingebretsen et al., Circ, Rs., 40: 474-484, 1977). Beads (10-15) were placed near one end to guinea pig papillary muscles mounted horizontally in a bath perfused with Krebs-Henseleit solution at 30 degrees C and stimulated at 0.2 Hz. The beads produced increased tension and elevation and slight lengthening of the plateau potential when [k+]o = 3.8 mM. After depolarization to a resting potential of -49 mV with [K+]o = 22 mM, isoproterenol beads restored contraction to a comparable extent as occurred with 10(-8) M soluble drug. During field stimulation, action potentials were initiated at the site of bead application and spread decrementally. When beads were placed distal to the site of point stimulation, virtually no excitation could be obtained from cells in the vicinity of the beads. When they were placed close to the stimulating electrode, the beads increased excitability and typical slow action potentials spread to the other end of the muscle. These potentials had the characteristics associated with the slow inward Ca2+ current. The slow channel blocker, D-600, blocked responses to isoproterenol beads. Tetrodotoxin caused responses similar to those obtained with K+ depolarization. The beads probably act by stimulating only a small fraction of the papillary muscle catecholamine receptors. Spread of action potentials from these sites and propagated tension depend on Ca2+ influx, but the nature of an intermediate messenger involved in the propagation of contractions is unknown.

Metabolism of adenine nucleotides in the cultured fetal mouse heart

Intact beating fetal mouse hearts in organ culture were deprived of oxygen and glucose for up to 4 h, resulting in loss of beating, an 80% fall in ATP, reduction of energy charge from 0.85 to 0.48, and doubling of total nucleoside concentration. Radiolabeled adenine nucleotides were degraded to hypoxanthine and inosine, which were lost from the hearts into the medium during the deprivation period. Adenosine and adenine also appeared in the medium when adenosine deaminase was inhibited. After 24 h of O2 and glucose resupply, ATP returned to 60% of control, and energy charge rose to 0.76. Labeled nucleosides and bases remaining in the heart or exogenous labeled adenine were utilized to resynthesize ATP. [14C]glycine was rapidly taken up by recovering hearts but was not used for de novo adenine nucleotide synthesis. Ability to recover ATP and spontaneous contraction appear related to residual nucleotide and nucleoside content rather than to energy charge.

Contractile and biochemical responses of cardiac and skeletal muscle to isoproterenol covalently linked to glass beads

The effects of (-)-isoproterenol covalently linked to glass beads on inotropic state, cyclic AMP concentration, and phosphorylase b to a conversion was studied in cat and guinea pig papillary muscles. Biochemical responses also were measured in mouse diaphragm sections. In cat papillary muscles under normal conditions and in guinea pig muscles partly depolarized with 22 mM K+ an increased inotropic state and phosphorylase activation could be dissociated from the formation of cyclic AMP. This contrasts with close correlation reported between isometric tension and cyclic AMP concentration in guinea pig papillary muscles exposed to varying concentrations of isoproterenol dissolved in the bath medium. The cyclic nucleotide did increase in guinea pig papillary muscles exposed to a freshly prepared batch of isoproterenol beads and in the mouse diaphragms. The type and age of the bead preparation had marked effects on all responses that were measured and on the rate of leakage of biologically active products from the beads. Nevertheless, experimental conditions could be obtained under which the initiation of the contractile and biochemical responses was probably limited to intense stimulation of receptors at or near the points of contact between beads and muscle and not due to gross leakage into the bath. The results indicate that cyclic AMP is probably involved in the initiation but not the propagation of the inotropic response of papillary muscles exposed to isoproterenol glass beads.

Stimulation of glycogenolysis by beta adrenergic agonists in skeletal muscle of mice with the phosphorylase kinase deficiency mutation (I strain)

The mechanism by which beta adrenergic agonist stimulate glycogenolysis in intact skeletal muscle was investigated in mice with the phosphorylase kinase deficiency mutation (I strain). Although extracts of I strain diaphragm muscle had only 3.7% of the phosphorylase kinase activity found in extracts of the control strain (C57BL), incubation of I strain hemidiaphragms in Krebs-Ringer bicarbonate buffer with either isoproterenol or epinephrine resulted in a stimulation of the rate of glycogenolysis. In C57BL diaphragms, the EC50 values for isoproterenol and epinephrine were 2 and 14 nM, respectively. With I strain diaphragms, dl-isoproterenol or l-epinephrine stimulated glycogenolysis as a linear function of the log of the drug concentration with no apparent plateau of response up to concentrations of 30 to 40 mugM. For each 10-fold increase in drug concentration, isoproterenol and epinephrine stimulated glycogenolysis in I strain muscles an additional 0.37 to 0.42 mg/g/hr, a slope in the concentration-response relationship of 0.17 and 0.37, respectively, of that measured in C57BL diaphragms at concentrations around the EC50. The highest glycogenolytic response measured in I strain hemidiaphragms (at 40 mugM isoproterenol) was 80% of the maximal catecholamine-stimulated glycogenolysis in C57BL diaphragms. Both 4 nM and 4 mugM isoproterenol, in a concentration-dependent manner, stimulated phosphorylase b to a conversion in I and C57BL diaphragms and increased cyclic adenosine 3':5'-monophosphate (cyclic AMP) concentrations. The glycogenolytic response to 10.1 nM dl-isoproterenol in both I and C57BL diaphragms was blocked by 34 nM l-propranolol but not by 34 nM d-propranolol. The response to 4 mugM isoproterenol was enhanced by the cyclic nucleotide phosphodiesterase inhibitors papaverine (27 mugM) or dl-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724, 3 mugM). From the results of these studies, we conclude: 1) Catecholamines stimulate glycogenolysis in skeletal muscle of I mice, as in C57BL mice, by interacting with the beta adrenergic receptor, thereby increasing tissue cyclic AMP concentrations and stimulating phosphorylase b to a conversion. 2) alternative hypotheses for the mechanism of the catecholamine-stimulated decrease in glycogen concentration in I skeletal muscle-inhibition of glycogen synthesis, hyposia and 5'-AMP stimulation of phosphorylase b activity-have been ruled out. 3) the activity of the mutant phosphorylase kinase, although it is only 3.7% of that in extracts of C57BL muscle, is sufficient to produce phosphorylase b to a conversion and thereby account for the glycogenolytic response of I strain muscle to catecholamines.

The role of cyclic adenosine 3', 5'-monophosphate and calcium in the regulation of contractility and glycogen phosphorylase activity in guinea pig papillary muscle

We studied the relationships between the positive inotropic effects of isoproterenol, increased frequency of contraction or paired electrical stimulation, and cyclic AMP concentration and phosphorylase activity in isolated guinea pig papillary muscles. The minimum concentration of isoproterenol (10 nM) that augmented isometric force development increased cyclic AMP concentration. However 100 nM isoproterenol was required to increase the phosphorylase activity ratio (-AMP/+AMP) from 0.15 +/- 0.03 to 0.25 +/- 0.03. After addition of 1 muM isoproterenol to the bath, cyclic AMP increased within 0.5 minute from 0.58 +/- 0.03 to 1.04 +/- 0.13 mol/kg (wet weight), peak contractile force was elevated 2-fold at 1 minute, and the phosphorylase activity ratio rose to 0.40 +/- 0.02 in 4 minutes. Although an increase in contraction frequency (6/min to 36/ min) and paired stimulation produced more than a 3-fold increase in peak contractile force, there were no changes in cyclic AMP and phosphorylase activity. The cyclic AMP concentration during diastole was 0.60 +/- 0.04 and in midsystole, 0.55 +/- 0.03 mumol/kg. Anoxia increased the phosphorylase activity ratio from 0.19 +/-0.02 to 0.41 +/- 0.04 without elevation of cyclic AMP concentration. Removal of Ca2+ from the bathing medium prevented active force development and the anoxic increase in phosphorylase activity, but did not prevent the isoproterenol-induced increase in cyclic AMP and phosphorylase. These results suggest that cyclic AMP is a factor in the catecholamine-induced enhancement of inotropic state. However, it does not appear to play a role in the maintained augmentation of inotropic state produced by increased contraction frequency and paired stimulation, nor does the concentration of the cycle nucleotide appear to vary during the contraction cycle or during anoxia. Extracellular Ca2+ is required for contraction, the positive inotropic aciton of catecholamines and phosphorylase b to a conversion by anoxia.

Enzymes regulating glycogen metabolism in swine subcutaneous adipose tissue. I. Phosphorylase and phosphorylase phosphatase

Glycogen phosphorylase from swine adipose tissue was purified nearly 700-fold using ethanol precipitation, DEAE-cellulose adsorption, AMP-agarose affinity chromatography, and agarose gel filtration. The purified enzyme migrated as one major and several minor components during polyacrylamide gel electrophoresis. Activity was associated with the major component and at least one of the minor components. The molecular weight of the disaggregated, reduced, and alkylated enzyme, estimated by polyacrylamide gel electrophoresis performed in the presence of sodium dodecyl sulfate, was 90,000. Stability of the purified enzyme was considerably increased in the presence of AMP. The isoelectric pH of the enzyme in crude homogenates was 6.3. The sedimentation coefficient of the purified enzyme (7.9 S) and that in crude homogenates (7.3 S) was determined by sucrose density gradient sedimentation. Optimal pH for activity was between pH 6.5 and 7.1. Apparent Km values for glycogen and inorganic phosphate were 0.9 mg/ml and 6.6 mM, respectively. The Ka for AMP was 0.21 mM. Enzyme activity was increased by K2SO4, KF, KCl, and MgCl2 and decreased by NaCl, Na2SO4, D-glucose, and ATP. Inhibition by glucose was noncompetitive with the activator AMP; inhibition by ATP was partially competitive with AMP. The purified enzyme was activated by incubation with skeletal muscle phosphorylase kinase. Enzyme in crude homogenates was activated by the addition of MgCl2 and ATP; activation was not blocked by addition of protein kinase inhibitor, suggesting that phosphorylase kinase in homogenates of swine adipose tissue is present largely in an activated form. Deactivation of phosphorylase a by phosphorylase phosphatase was studied using enzyme purified approximately 200-fold from swine adipose tissue by ethanol precipitation, DEAE-cellulose chromatography, and gel filtration. The Km of the adipose tissue phosphatase for skeletal muscle phosphorylase a was 6 muM. The purified swine adipose tissue phosphorylase, labeled with 32-P, was inactivated and dephosphorylated by the adipose tissue phosphatase. Dephosphorylation of both skeletal muscle and adipose tissue substrates was inhibited by AMP and glucose reversed this inhibition. Several lines of evidence suggest that AMP inhibition was due to an action on the substrate rather than on the enzyme. We have previously reported that the system for phosphorylase activation in rat fat cells differs in some important characteristics from that in skeletal muscle. However, both swine fat phosphorylase and phosphorylase phosphatase have major properties very similar to those described for the enzymes from skeletal muscle.

Enzymes regulating glycogen metabolism in swine subcutaneous adipose tissue. II. Glycogen synthase

Glycogen synthase from swine adipose tissue was purified to apparent homogeneity using ethanol precipitation, DEAE chromatography, and affinity chromatography utilizing glucosamine 6-phosphate as the ligand. The purified enzyme migrated as a single protein component during electrophoresis on polyacrylamide gels at pH 7.3 although some protein failed to enter the running gel. Enzyme incubated with sodium dodecyl sulfate (SDS) migrated as one component (mol wt similar to 90,000) on SDS-polyacrylamide gel electrophoresis. The enzyme was relatively unstable at all stages of the purification procedure, but stability was increased in the presence of glucose 6-phosphate, UDPG, or glycerol. The isoelectric point of the purified enzyme and of enzyme activity in crude homogenates was pH 4.8. The sedimentation coefficient of the enzyme in crude homogenates was 8.5 S. The pH-activity profile showed an optimum at pH 7.8 in the absence of glucose 6-phosphate but no definable optimum between pH 7.0 and 9.2 in its presence. The Km of glycogen synthase I for UDPG was 250 muM in the absence and 37 muM in the presence of glucose 6-phosphate; the K-a for glucose 6-phosphate was 18 mu-M. The K-m of glycogen synthase D for UDPG was 130 mu-M in the presence of glucose 6-phosphate; the Ka for glucose 6-phosphate was 1 mM. The anions sulfate and phosphate activated the enzyme when assays were performed in the absence of glucose 6-phosphate. Fluoride produced activation of enzyme assayed either in the presence or in the absence of glucose 6-phosphate.

Phosphorylase kinase mediating the effects of cyclic AMP in muscle

In the classic view of the control of phosphorylase b to a conversion by catecholamines, cyclic AMP acts as the second messenger stimulating the activity of cyclic AMP-dependent protein kinase to covalently modify phosphorylase kinase. Phosphorylation of phosphorylase kinase converts this enzyme form with a nonactivated to an activated form with a markedly higher activity at pH 7. There is now considerable evidence that the activity of phospphorylase kinase is also regulated by changeds in the Ca-2+ concentration. The activity of both nonactivated and activated phosphorylase kinase is stimulated by Ca-2+ in the range of concentrations that have been reported to occur in the sacroplasm of contracting muscle, with the activated pphosphorylase kinase having a lower K-alpha for Ca-2+. Thus there are at leaset two mechanisms for the regulation of phosphorylase kinase activity in muscle. These mechanisms may act independently or in concert in controlling glycogenolysis stimulated by catecholamines, anoxia, or tetanic electrical stimulation...