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Inositol phosphates: Effect on calcium release from sarcoplasmic reticulum of cardiac muscle
J Mel Cell Cardiol21 103INOSlTOL MUSCLE. sity of
(Supplement
PHOSPHATES: A. Lochner, Stellenbosch
II) (1989)
EFFECT ON CALCIUM RELEASE MRC Centre for R. Bester. Medical School, Tygerberg,
FROM SARCOPLASMIC Molecular and Cellular Republic of South
RETICULUM Biology, Africa.
OF CARDIAC Univer=
Increased phosphatidylinositol metabolism have been demonstrated in conditions that increase mechanical activity of the heart (1.2). However, controversy exists 2+ whether inositoltrisphosphate (IP ) acts as a second messenger in the release of Ca from the sarcoplasmic reticulum ( 3 R) in heart muscle. This study was therefore under= taken to assess the ability of inositol trisphosphate (IP 1, inositol tetrakisphos= phate (IP ), inositol bisphosphate (IP2) and inositol pen 2 akisphosphate (IP ) to re= lease Ca2$ from isolated SR vesicles from cardiac muscle. Using a purified 2 R prepara= ti n it was demonstrated that IP a (5 PM) IS of releasing more than 60% of the . capable P+7 Ca taken up by these vesicles. dose-response g+elationship showed maximal release at 5 ~.IM IP . lPq (5 )JM) also caused release of Ca , while IP and IP had no effect. These resu 3 ts were obtained both in the absence2znd presence zf oxala 2 e. Ruthenium red a blocker of the terminal cisternae Ca channels, almost comple$;ly abo= (20 UN), lished IP -induced Ca2+ release, while it had no effect on IP,,-ig$uced Ca release. These res I?4Its suggest the possibility of two mechanisms of SR Ca release. 1. 2.
104P
Poggioli, Woodcock,
J. et al., E.A. et al.,
Febs. Circ.
Lett. Res.
206, 292, 1986. 61, 625, 1987.
-PURINERGIC RECEPTOR MEDIATED PHOSPHOINOSITIDES(P1) METABOLISM IN CULTURED M.Yamada. M.Yokoyama, Y.Hamamori, R.Miyake, Y.Matsuda, E&RYONIC CARDIOMYOCYTES. K.Hirata, A.Yatani, H.Akita, H.Fukuzaki. Department of Internal Medicine(Section I), Kobe University, School of Medicine, Kobe, Japan Extracellular ATP has been found to exert inotropic and chronotropic effects on the PI-metabolism has been shown to be coupled to heart. In several types of cells, P2-receptor. We examined ATP-mediated signal transduction in highly-enriched(80X of cardiomyocytes) cultured embryonic mouse ventricular cardiomyocytes, as few studies have been made on the heart. ATP stimulated accumulation of inositol phosphates (IP ,IP ,IP ) in time-and dose-dependent manners with ED of 10uM. 8-Pienyltheaphylline, a Pl-antagonist, never antagonised 5?his effect. APCPP, a selective P2-agonist, had an effect similar to that of ATP. The order of agonist potency was ATPYS,ATP,ADP>APPNP>APCPP>APPCP,AMP,Adenosine. According to these data, ATP appears to stimulate PI-metabolism through P2-receptor of cardiomyocytes. This response was inhibited almost completely by the phorbol ester(TPA, PDBu) with ID of lnM, but attenuated only partly by prior 24-h exposure of cells to lOOng/ml o z" islet-activating protein(IAP). The latter indicates that IAP-substrate GTP-binding proteins might not be the sole mediator of this signal transduction system. Functional significance of P2-receptor mediated PI-metabolism in cardiomyocytes is unknown and now under investigation.
105INCREASED INCSITOL TRISPiICSPHATE KINASE IN mF%IC RAT HEART. H.kawaguchi, Hokkaido University, Sappcro, Japan M.Shouki, O.Takakuwa, T.Ono, H.Yasuda. Free cytosolic calcium plays an important role in the developnent of cell proliferation. Inositol 1,4,5-trisphosphate (IP3) is a second messenger releasing intracellular Caz+ into the cytosol. It has recently been proposed that 1,3,4,5tetrakisphosphate (IP4), which is formed from IP3 by IP3-kinase, act with IP3 as a second messenger by promoting extracellular Ca*+ entry. We determined IP3kinase activity in hypertrophied rat heart to investigate the relationship between cardiac hypertrophy and Caz*. Kxperiments were carried out on lo-30-weekold male spontaneously hypertensive rat (SHR) and age-matched normotensive Wistar-kyoto rat (WKY). Rat heart was homogenized and centrifuged at 105,OOOxg for 90 min. The resultant supernatsnt was used cytosolic fraction. IP3-kinase activity was detected in only cytosolic fraction. Mga*, ATP and Caa+ stimulated its activity. Optimal pH was 7.4 and 9.5. There was no difference between SHR and WKY aged 10 weeks in IP3-kinase activity at pH 7.4 and 9.5. Its activity was increased up to 2.5 times in SHR and 1.25 times in WKY aged 30 weeks. Increased IP4 formation may lead Ca2+ into cell. These results may suggest that IP3 and IP4 have an important role in cardiac hypertrophy in SHR. Key words; Inositol trisphosphate, Inositol trisphosphate kinase, Cardiac hypertrophy
s.35
(Supplement
PHOSPHATES: A. Lochner, Stellenbosch
II) (1989)
EFFECT ON CALCIUM RELEASE MRC Centre for R. Bester. Medical School, Tygerberg,
FROM SARCOPLASMIC Molecular and Cellular Republic of South
RETICULUM Biology, Africa.
OF CARDIAC Univer=
Increased phosphatidylinositol metabolism have been demonstrated in conditions that increase mechanical activity of the heart (1.2). However, controversy exists 2+ whether inositoltrisphosphate (IP ) acts as a second messenger in the release of Ca from the sarcoplasmic reticulum ( 3 R) in heart muscle. This study was therefore under= taken to assess the ability of inositol trisphosphate (IP 1, inositol tetrakisphos= phate (IP ), inositol bisphosphate (IP2) and inositol pen 2 akisphosphate (IP ) to re= lease Ca2$ from isolated SR vesicles from cardiac muscle. Using a purified 2 R prepara= ti n it was demonstrated that IP a (5 PM) IS of releasing more than 60% of the . capable P+7 Ca taken up by these vesicles. dose-response g+elationship showed maximal release at 5 ~.IM IP . lPq (5 )JM) also caused release of Ca , while IP and IP had no effect. These resu 3 ts were obtained both in the absence2znd presence zf oxala 2 e. Ruthenium red a blocker of the terminal cisternae Ca channels, almost comple$;ly abo= (20 UN), lished IP -induced Ca2+ release, while it had no effect on IP,,-ig$uced Ca release. These res I?4Its suggest the possibility of two mechanisms of SR Ca release. 1. 2.
104P
Poggioli, Woodcock,
J. et al., E.A. et al.,
Febs. Circ.
Lett. Res.
206, 292, 1986. 61, 625, 1987.
-PURINERGIC RECEPTOR MEDIATED PHOSPHOINOSITIDES(P1) METABOLISM IN CULTURED M.Yamada. M.Yokoyama, Y.Hamamori, R.Miyake, Y.Matsuda, E&RYONIC CARDIOMYOCYTES. K.Hirata, A.Yatani, H.Akita, H.Fukuzaki. Department of Internal Medicine(Section I), Kobe University, School of Medicine, Kobe, Japan Extracellular ATP has been found to exert inotropic and chronotropic effects on the PI-metabolism has been shown to be coupled to heart. In several types of cells, P2-receptor. We examined ATP-mediated signal transduction in highly-enriched(80X of cardiomyocytes) cultured embryonic mouse ventricular cardiomyocytes, as few studies have been made on the heart. ATP stimulated accumulation of inositol phosphates (IP ,IP ,IP ) in time-and dose-dependent manners with ED of 10uM. 8-Pienyltheaphylline, a Pl-antagonist, never antagonised 5?his effect. APCPP, a selective P2-agonist, had an effect similar to that of ATP. The order of agonist potency was ATPYS,ATP,ADP>APPNP>APCPP>APPCP,AMP,Adenosine. According to these data, ATP appears to stimulate PI-metabolism through P2-receptor of cardiomyocytes. This response was inhibited almost completely by the phorbol ester(TPA, PDBu) with ID of lnM, but attenuated only partly by prior 24-h exposure of cells to lOOng/ml o z" islet-activating protein(IAP). The latter indicates that IAP-substrate GTP-binding proteins might not be the sole mediator of this signal transduction system. Functional significance of P2-receptor mediated PI-metabolism in cardiomyocytes is unknown and now under investigation.
105INCREASED INCSITOL TRISPiICSPHATE KINASE IN mF%IC RAT HEART. H.kawaguchi, Hokkaido University, Sappcro, Japan M.Shouki, O.Takakuwa, T.Ono, H.Yasuda. Free cytosolic calcium plays an important role in the developnent of cell proliferation. Inositol 1,4,5-trisphosphate (IP3) is a second messenger releasing intracellular Caz+ into the cytosol. It has recently been proposed that 1,3,4,5tetrakisphosphate (IP4), which is formed from IP3 by IP3-kinase, act with IP3 as a second messenger by promoting extracellular Ca*+ entry. We determined IP3kinase activity in hypertrophied rat heart to investigate the relationship between cardiac hypertrophy and Caz*. Kxperiments were carried out on lo-30-weekold male spontaneously hypertensive rat (SHR) and age-matched normotensive Wistar-kyoto rat (WKY). Rat heart was homogenized and centrifuged at 105,OOOxg for 90 min. The resultant supernatsnt was used cytosolic fraction. IP3-kinase activity was detected in only cytosolic fraction. Mga*, ATP and Caa+ stimulated its activity. Optimal pH was 7.4 and 9.5. There was no difference between SHR and WKY aged 10 weeks in IP3-kinase activity at pH 7.4 and 9.5. Its activity was increased up to 2.5 times in SHR and 1.25 times in WKY aged 30 weeks. Increased IP4 formation may lead Ca2+ into cell. These results may suggest that IP3 and IP4 have an important role in cardiac hypertrophy in SHR. Key words; Inositol trisphosphate, Inositol trisphosphate kinase, Cardiac hypertrophy
s.35