RESUMEN
Ca2+ release from skeletal sarcoplasmic reticulum (SR) could be regulated by at least three mechanisms: 1) Ca2+, 2) calmodulin, and 3) Ca2+/calmodulin-dependent phosphorylation. Bell-shaped Ca(2+)-dependence of Ca2+ release from both actively- and passively-loaded SR vesicles suggest that opening and closing of the Ca2+ release channel could be regulated by [Ca2+o]. The time- and concentration-dependent inhibition of Ca2+ release from skeletal SR by calmodulin was also studied using passively-Ca2+ loaded SR vesicles. Up to 50% of Ca2+ release was inhibited by calmodulin (0.01-0.5 microM); this inhibition required 5-15 min preincubation time. The hypothesis that Ca2+/calmodulin-dependent phosphorylation of a 60 kDa protein regulates Ca2+ release from skeletal SR was tested by stopped-flow fluorometry using passively-Ca2+-loaded SR vesicles. Approximately 80% of the initial rates of Ca(2+)-induced Ca2+ release was inhibited by the phosphorylation within 2 min of incubation of the SR with Mg-ATP and calmodulin. We identified two types of 60 kDa phosphoproteins in the rabbit skeletal SR, which was distinguished by solubility of the protein in CHAPS. The CHAPS-soluble 60 kDa phosphoprotein was purified by column chromatography on DEAE-Sephacel, heparin-agarose, and hydroxylapatite. Analyses of the purified protein indicate that the CHAPS-soluble 60 kDa protein is an isoform of phosphoglucomutase (PGM). cDNAs encoding isoforms of PGM were cloned and sequenced using synthetic oligonucleotides. Two types of PGM isoforms (Type I and Type II) were identified. The translated amino acid sequences show that Type II isoform is SR-form.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Calcio/metabolismo , Músculos/metabolismo , Retículo Sarcoplasmático/metabolismo , Animales , Transporte Biológico , Calmodulina/metabolismo , Técnicas In Vitro , Contracción Muscular , Fosfoglucomutasa/metabolismo , Fosfoproteínas/metabolismo , FosforilaciónRESUMEN
Doxorubicin, an anthracycline glycoside antibiotic which has been widely used for treatment of several types of cancer (Goormaghtigh and Ruysschaer, 1984), displays a clinically important cardiac toxicity (Young et al., 1981) that can be dissociated from the antitumor activity. Although the main sites of toxicity have been postulated to be on the muscle membranes (Goormaghtigh and Ruysschaer, 1984; Harris and Doroshow, 1985), no information is available for a direct doxorubicin effect on the Ca2+ fluxes in cardiac sarcoplasmic reticulum (SR). Previous studies have shown that micromolar doxorubicin triggers Ca2+ release from skeletal SR vesicles (Zorzato et al., 1985). The objective of this study was to examine the effect of doxorubicin or caffeine on Ca2+ fluxes in cardiac SR in the presence of various Ca2+ release inhibitors. Addition of either doxorubicin (C1/2 = 5 microM), or caffeine (C1/2 = 0.8 mM) triggered Ca2+ release from canine cardiac SR loaded with 45Ca2+ in the presence of 2 mM ATP. The maximal amount of Ca2+ release triggered by doxorubicin (38% of the total loaded Ca2+) was significantly higher than that released by caffeine (25%). Plots of the amount of Ca2+ release triggered by 20 microM doxorubicin or 2 mM caffeine vs. free Ca2+ concentration were a bell-shaped, with maximal Ca2+ release at 0.2 microM Ca2+. Ca2+ release triggered by either 20 microM doxorubicin or 2 mM caffeine was inhibited by ruthenium red (0.1 to 2 microM), ryanodine (1 to 100 microM) or tetracaine (0.1 to 1 mM), whereas 2 mM caffeine did not further activate Ca2+ release triggered by 50 microM doxorubicin, suggesting that the drugs may share the same Ca2+ release channel.
Asunto(s)
Calcio/metabolismo , Doxorrubicina/farmacología , Miocardio/metabolismo , Retículo Sarcoplasmático/efectos de los fármacos , Animales , Cafeína/farmacología , Bloqueadores de los Canales de Calcio/farmacología , Perros , Corazón/efectos de los fármacos , Cinética , Miocardio/ultraestructura , Retículo Sarcoplasmático/metabolismoRESUMEN
Patients recovering from myocardial infarction (MI) or other heart diseases at St. Francis Hospital, Hartford, Ct, were educated by videotape or by staff lectures on alternating weeks. Both programs included the following: risk factors for MI, medications, diet, MI symptoms and life style changes. Patients were interviewed before and after the educational program. The MI patients under the age of 60 scored equally well on an informational test irrespective of the type of education program experienced. Older MI patients were significantly more likely to complete the educational program when it was given by videotape; those discontinuing attendance at lectures were less psychologically motivated to participate but were not necessarily more ill. Overall, higher education was the single most significant predictor of superior scores following patient education. Implications for the coronary care ward of the success of videotape in educating MI patients are discussed.