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Stretch-induced atrial natriuretic peptide secretion and its positive modulation by phorbol ester
Stretch-induced atrial natrimetic peptide secretion and its positive modulation by phorbol ester Ruskoaho, H.J., V u o l t e e n a h o *, O. a n d Leppiiluoto *, P.J. Dep~.ments of Ph~emacology and * Toxicology and Physiology, University of Oulu, Kajaanintie 52 1), SF.90220 Oulu, Finland
Stretching of atrial myocytes stimulates atrial natriuretic peptide (ANP) secretion (Lang et al., 1985) but the cellular processes linking mechanical distension to ANP release are unknown. We reported that in the perfused, spontaneously beating rat hearts, phorbol esters, which mimic the action of diacyiglycerol by acting directly on protein kinase C, increase dose-dependently immunoreactive ANP (IR-ANP) secretion into theperfusion fluid, and phorbol ester combined with C a 2+ ionophore A23187, C a 2+ channel agonist Bay k8644 or forskolin produced a synergistic effect (Ruskoaho et al., 1985; 1986) These results suggested a possible role for calcium-activated protein kinase C in the regulation of basal ANP secretion. This study was designed to examine whether or not protein kinase C activation by phorbol ester affects atrial stretch-induced ANP secretion. In addition, the importance of Ca 2+ as possible intracellular messenger in stretchstimulated ANP released was studied. The modified perfused rat heart preparation that enabled the stepwise distension of the right atrium was used an experimental model for stretch-stimulated ANP release. The increase in right atrial pressure (2.65 + 0.13 mm Hg) was accompanied by an increase in the perfusate IR-ANP concentration (from 3.3 + 1.1 ng/5 rain to 13.9 + 2.0 ng/5 h~n, p < 0.05, n -- 14) Incre ~.'~. of right atrial pressure in the presence of a phorbo| ester, TPA, known to stimulate protein kinase C activity in heart cells, resulted in significantly greater increase in the perfusate IR-ANP concentration than after vehicle infusion. The calculated ANP increase corresponding to the ~. mm Hg increase in the right atrial pressure was 1.52-fold in the control group and 1.84-fold when 10 nM TPA was infused (p < 0.05). Infusion of TPA at a dose of 24 nM ft~ther increased the stretch-induced ANP release by causing 2.22-fold (p < 0.01) increase in IR-ANP secretion. As judged by gel filtration chromatrography, abnormal release of the large molecular weight stored ANP could not account for the secretory response to phorbol ester. A phorbol ester analog, 4a-phorbot-12,13-didecanoate, which is incapable of binding to and activating protein kinase C, was inactive as an ANP secretagogue. In contrast, drugs known to increase the concentration of intracellular Ca 2+ in myocytes, Bay K8644 (3 and 6 pM) and forskolin (0.14/zM) significantly inhibited the stretch-stimulated ANP release. This study shows that phorbol ester enhance atrial stretch-stimulated ANP secretion from the isolated perfused heart suggesting that protein kinase C activity is positively coupled to the stretch-induced ANP release. The results further demonst~te the negative effect of increase in intracellular C a 2+ o n stretch-induced ANP release. References Lang R., Th~lken H., Ganten D., Luft F., Ruskoaho H., Unger T., 1985, Mature 314, 264. Ruskoaho H., Toth M., Lang R., 1985, Biochem. Biophys. Res. Commun. 133, 581. ~'askoaho H., Toth M., Ganten D., Unger T., Lang R., 1986, Biochem. Biophys. Res.Commun. 139, 266.
EndotheUn-I and sarafotoxin stimulate atrial natriuretic peptide secretion from the peffused rat heart M~mtymaa, P., Pitk~inen, M., Lepp~iluoto *, J. a n d R u s k o a h o , H. Departments of Pharmacology and * Toxicology and Physiology, University of Oulu, Kajaanintie 52 D, SF-90220 Oul~ Finland
Atrial wall stretch is a major factor in the regulati¢n of the release of ANP (Lang et al., 1985); however, the precise cellular mechanisms linking mechanical distension to hormonal release are unknown. To examine the role of
Stretching of atrial myocytes stimulates atrial natriuretic peptide (ANP) secretion (Lang et al., 1985) but the cellular processes linking mechanical distension to ANP release are unknown. We reported that in the perfused, spontaneously beating rat hearts, phorbol esters, which mimic the action of diacyiglycerol by acting directly on protein kinase C, increase dose-dependently immunoreactive ANP (IR-ANP) secretion into theperfusion fluid, and phorbol ester combined with C a 2+ ionophore A23187, C a 2+ channel agonist Bay k8644 or forskolin produced a synergistic effect (Ruskoaho et al., 1985; 1986) These results suggested a possible role for calcium-activated protein kinase C in the regulation of basal ANP secretion. This study was designed to examine whether or not protein kinase C activation by phorbol ester affects atrial stretch-induced ANP secretion. In addition, the importance of Ca 2+ as possible intracellular messenger in stretchstimulated ANP released was studied. The modified perfused rat heart preparation that enabled the stepwise distension of the right atrium was used an experimental model for stretch-stimulated ANP release. The increase in right atrial pressure (2.65 + 0.13 mm Hg) was accompanied by an increase in the perfusate IR-ANP concentration (from 3.3 + 1.1 ng/5 rain to 13.9 + 2.0 ng/5 h~n, p < 0.05, n -- 14) Incre ~.'~. of right atrial pressure in the presence of a phorbo| ester, TPA, known to stimulate protein kinase C activity in heart cells, resulted in significantly greater increase in the perfusate IR-ANP concentration than after vehicle infusion. The calculated ANP increase corresponding to the ~. mm Hg increase in the right atrial pressure was 1.52-fold in the control group and 1.84-fold when 10 nM TPA was infused (p < 0.05). Infusion of TPA at a dose of 24 nM ft~ther increased the stretch-induced ANP release by causing 2.22-fold (p < 0.01) increase in IR-ANP secretion. As judged by gel filtration chromatrography, abnormal release of the large molecular weight stored ANP could not account for the secretory response to phorbol ester. A phorbol ester analog, 4a-phorbot-12,13-didecanoate, which is incapable of binding to and activating protein kinase C, was inactive as an ANP secretagogue. In contrast, drugs known to increase the concentration of intracellular Ca 2+ in myocytes, Bay K8644 (3 and 6 pM) and forskolin (0.14/zM) significantly inhibited the stretch-stimulated ANP release. This study shows that phorbol ester enhance atrial stretch-stimulated ANP secretion from the isolated perfused heart suggesting that protein kinase C activity is positively coupled to the stretch-induced ANP release. The results further demonst~te the negative effect of increase in intracellular C a 2+ o n stretch-induced ANP release. References Lang R., Th~lken H., Ganten D., Luft F., Ruskoaho H., Unger T., 1985, Mature 314, 264. Ruskoaho H., Toth M., Lang R., 1985, Biochem. Biophys. Res. Commun. 133, 581. ~'askoaho H., Toth M., Ganten D., Unger T., Lang R., 1986, Biochem. Biophys. Res.Commun. 139, 266.
EndotheUn-I and sarafotoxin stimulate atrial natriuretic peptide secretion from the peffused rat heart M~mtymaa, P., Pitk~inen, M., Lepp~iluoto *, J. a n d R u s k o a h o , H. Departments of Pharmacology and * Toxicology and Physiology, University of Oulu, Kajaanintie 52 D, SF-90220 Oul~ Finland
Atrial wall stretch is a major factor in the regulati¢n of the release of ANP (Lang et al., 1985); however, the precise cellular mechanisms linking mechanical distension to hormonal release are unknown. To examine the role of