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PUBMED | Cardiovascular research | 9659455 | Stimulation of Ca-induced Ca release only transiently increases the systolic Ca transient: measurements of Ca fluxes and sarcoplasmic reticulum Ca. | OBJECTIVE: To investigate the effects of stimulating calcium induced Ca release with low concentrations (100-200 microM) of caffeine and, in particular, to study the cellular mechanisms responsible for the transient responses found previously. METHODS: Experiments were performed on isolated rat ventricular myocytes. Intracellular calcium concentration (i) was measured with Indo-1, the cells were voltage-clamped with the perforated patch technique and sarcoplasmic reticulum (s.r.) Ca content was estimated from the integral of the caffeine-evoked current. RESULTS: The systolic Ca transient produced by the first depolarization in the presence of caffeine was larger than the control. Over the next few pulses the magnitude of the Ca transient returned to control levels despite the maintained presence of caffeine. The s.r. Ca content was decreased by 9% after one pulse in caffeine and by 21% after several pulses in caffeine. The first pulse in the low concentration of caffeine was followed by an enhanced inward (Na-Ca exchange) current tail indicating increased efflux of calcium from the cell. The extra loss of calcium calculated from the tail current agreed quantitatively with that from the change of s.r. Ca content. CONCLUSIONS: These results show that stimulating calcium induced calcium release produces only a transient increase of the systolic Ca transient. This is due to the larger Ca transient decreasing the s.r. Ca content. It is concluded that any agent whose sole mode of action is stimulation of calcium-induced calcium release will not produce a maintained inotropic effect. The consequences of this for the effects of other modulators of calcium induced calcium release are discussed. | Trafford A W AW; D铆az M E ME; Eisner D A DA | 1998-03-02 | pubmed24n0320.xml | 9 | Metabolism & Diabetes | 1995-1999 |
PUBMED | Cardiovascular research | 9659456 | Stimulation of P2Y receptors activates c-fos gene expression and inhibits DNA synthesis in cultured cardiac fibroblasts. | OBJECTIVES: The aims of this study were to determine (1) whether neonatal rat cardiac fibroblasts (CAFB) express P2Y receptors; (2) whether CAFB respond to extracellular ATP by inducing expression of c-fos mRNA; and (3) whether extracellular ATP modulates norepinephrine (NE)-stimulated cell growth in CAFB. METHODS: Expression of P2Y1 and P2Y2 receptors and induction of c-fos were examined by Northern blot analysis. CAFB growth was assessed by measuringthymidine incorporation and DNA content. P2Y receptor pharmacology was studied using various ATP analogues. RESULTS: Northern blot analysis of polyA enriched RNA confirmed that at least 2 subtypes of P2Y receptors (P2Y1 and P2Y2) are expressed in cultured CAFB. Extracellular ATP induced the expression of c-fos mRNA through a pathway that was sensitive to inhibitors of protein kinase C (PKC), but not to inhibitors of intracellular Ca2+ signaling. Extracellular ATP inhibited the NE-stimulated increases in DNA content and inthymidine incorporation into DNA. Whereas the potency order for stimulation of c-fos expression was ATP = UTP > ADP > adenosine, the potency order to inhibit the NE-induced increase ofthymidine incorporation into DNA was ATP > ADP > UTP > adenosine. CONCLUSIONS: These data demonstrate that CAFB express both P2Y1 and P2Y2 receptor mRNA and that CAFB respond to P2Y receptor stimulation by induction of c-fos and inhibition of DNA synthesis. These findings suggest that the effects of ATP onthymidine incorporation into DNA and on expression of c-fos mRNA are exerted via distinct P2Y receptor subtypes. | Zheng J S JS; O'Neill L L; Long X X; Webb T E TE; Barnard E A EA; Lakatta E G EG; Boluyt M O MO | 1998-03-02 | pubmed24n0320.xml | 9 | Metabolism & Diabetes | 1995-1999 |
PUBMED | Cardiovascular research | 9659457 | High-density lipoprotein particles are large in patients with variant angina. | OBJECTIVE: Dyslipidemia in patients with coronary vasospasm may be characterized by low level of high-density lipoprotein (HDL)-cholesterol as well as apolipoprotein (apo) A-I but not high level of low-density lipoprotein-cholesterol. This study sought to examine the HDL particle size in patients with variant angina. METHODS: The HDL particle size was examined by analyzing serum lipid levels in 38 patients with variant angina to compare with those of 40 control subjects and 30 normocholesterolemic patients with stable effort angina. Also, actual HDL size distribution was assessed by electrophoresis. RESULTS: The HDL-cholesterol, apoA-I and apoA-II levels were all lower (P < 0.01 for each) in patients with variant angina and patients with stable effort angina as compared with control subjects. The apoA-II level was lower (P < 0.01) in patients with variant angina than in patients with stable effort angina. The apoA-I/apoA-II ratio was lower (P < 0.01) in patients with stable effort angina, but not in patients with variant angina as compared with control subjects. In contrast, the HDL-cholesterol/apoA-I ratio was higher in patients with variant angina than in control subjects (P < 0.01) and also patients with stable effort angina (P < 0.01). The slope of the regression line, comparing HDL-cholesterol and apoA-I levels, was greater in patients with variant angina than in control subjects (P < 0.05) and patients with stable effort angina (P < 0.05), suggesting an increase in larger HDL particles. Native polyacrylamide gel electrophoresis revealed that HDL particles in patients with variant angina were skewed towards larger sizes compared with control subjects (P < 0.01) and patients with stable effort angina (P < 0.01). The abnormal serum lipid values were normalized in the patients with variant angina after the medical treatment and inactivation of the coronary spasm. CONCLUSION: High HDL-cholesterol/apoA-I levels associated with low serum HDL-cholesterol and apoA-I levels were characteristic in patients with variant angina, in whom HDL particles were large, cholesterol-rich and possibly malfunctioning. | Miwa K K; Yoshida N N; Nakagawa K K; Inoue H H | 1998-03-02 | pubmed24n0320.xml | 9 | Metabolism & Diabetes | 1995-1999 |
PUBMED | Cardiovascular research | 9659458 | Impairment of endothelium-dependent vasorelaxation in experimental atherosclerosis is dependent on gender. | OBJECTIVE: Nitric oxide. Importantly, the cholesterol diet induced a significantly and the extent of impairment of endothelium-dependent relaxation were associated with a reduced aortic sensitivity to S-nitroso-N-acetyl-D,L-penicillamine, which releases NO into the organ bath. In contrast, the aortic sensitivity to the organic nitrates pentaerythritol tetranitrate and isosorbide 5-nitrate, which release NO after enzymatic metabolization within the smooth muscle, was not reduced. CONCLUSIONS: These results suggest that the impairment of endothelium-dependent vasorelaxation induced by atherosclerosis is dependent on gender. This may be due to a greater degradation of extracellular NO in the vessel wall of males. | Kojda G G; H眉sgen B B; Hacker A A; Perings D D; Schnaith E M EM; Kottenberg E E; Noack E E | 1998-03-02 | pubmed24n0320.xml | 9 | Metabolism & Diabetes | 1995-1999 |