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Inotropic responses of mammalian cardiac muscle to acidosis can be predicted from the measured changes in intracellular pH and sodium
J Mol Cell Cardiol20 P-3
(Supplement
IV)(1988)
1 BUFFER POWER AND INTRACELLULAR pH OF HYPERTROPHIC PAPILLARY MUSCLE FROM FERRET. SBaudet, J.Noireaud, C.Leoty. Laboratory of General Physiology, E.N.V., University of Nantes CP 3013, F-44087 Nantes Cedex 03, France. The development of pressure overload hypertrophy of mammalian myocardium is associated with a decline in contractile function and prolongation of the isometric contraction. These changes may be due to abnormalities in intracellular pH (pHi) handling: this hypothesis has been tested in control ferrets and ferrets in which right ventricular hypertrophy was induced by banding the pulmonary artery. pHi of normal and hypertrophic papillary muscles from ferret heart were measured using pH-sensitive microelectrodes, filled with the ion-exchange resin proton cocktail (Fluka AG). The membrane potential was measured with a separate conventional KCI-filled microelectrode. In HEPES (5mM) buffered Tyrode solution (extracellular pH (pHo) 7.4, 34-36X) mean pHi was similar in the two types of muscles (control: 7.00 +/- 0.13 SD, n=21; hypertrophic: 7.06 +/0.21 SD, n=ll, P>O.l). On changing to Tyrode solution containing CO2 and HC03- (pHo 7.4, 34-36X) pHi became transiently acid in both cardiac tissues. In pathological cells, the calculated buffer power from the changes in pHi was 71.5 mM H+I pH units (+/- 5.0 SEM, n=6). Similar values were obtained in normal cells. Thus changes in the mechanical properties of hypertrophtc cardiac fibres are not due to a difference of pHi or buffering of resting cells. This work was supported by the Fondation myqathies and the Fondation Langlois.
pour
/a Racherche
Mtkiicale.
The Association
Frangaise
contre
/as
P-32 INHIBITION
OF Na-H EXCHANGE IN THE SHEEP CARDIAC PURKINJE FIBRE. M.L.WU a RD.Vaqhan-Jones. University Laboratory of Physiology, Parks Road, Oxford OX1 3PT. Na-H exchange is the principal mechanism regulating pHi in cardiac muscle following an intracellular acid load. We have investigated sOme mechanisms that can lead to inhibition of the exchange. Manoeuvres tpt raise cytoplasmic-s-AMP eg. addition of 25+M 3-isobutyl-l-methyl xanthine, 10 M isoprenaline or 10 M c-AMP slightly inhibit the rate of pH; recovery from an internal acid load (induced bv addition and then removal of 2Om'M NH4Cl) j35&5% inhibition at pHi 6.7, n=8; S.E.M.): Inhibition of aerobic metabolism (5mM CN) slows pH; recovery more effectivelv (5826% inhibition at pHi 6.9, n=lO) whereas inhibitiono? anaerobic metabolism (iOr&2deoxyglucose in glucose-free solution) greatly inhibits pHi-recovery (95&2% inhibition at pH; 6.8, n=4). Although reducino DH: stimulates the exchanaer. reducim pHo inhibits it.lIn two experiments , net acidef&x during pHi recove, was roqhl; equal to k[H+l," where n=O.5 and k depends on PH; (constant Na,). Hence at constant pHi, reducing-pa0 from 7.4-6.4 leads to a70% inhfbition of thgexchanger. Thus two important physiological factors that will affect Na-H exchange are (i) impairment of energy metabolism and (ii) extracellular acidosis. Supported by grants from the Brtish Heart Foundation & N.S.C. of Republic of China.
P-33 INOTROPIC RESPONSESOF MAMMALIAN CARDIAC MUSCLE I0 ACIL0SIS CAN BE PREDICTED FROM THE MEASURED CHANGES IN INTRACELLULAR pH AND SODIUM. R.D.Vaughan-Jones & C.Bountra. University Laboratory of Physiology, Parks Poad,Oxford OX1 3PT. Simultaneous measurement of pHi (ion-selective microelectrode, ISM) and twitch tension in isolated sheep cardiac Purkinje fibres or guinea-pig papillary muscle (HEPES buffered solutions, 100% 02), shows that the inotropic response to acidosis occurs only when there is a change in pH.i. However, a fall in pHi produced by reducing pHo (6.4) results in a negative inotropy, whereas the same fall in pHi produced at a pHo of 7.4 (removal of 1OmM NH Cl) can result in a positive inotropy. These different responses can be explained % y the observation that a fall in pHi raises intracellular Na activity (ai,).via stimulation of Na-H exchange. In papillary muscle, reducing pHi to 7.0 elevates aha (ISM) by about 4mM at pHo 7.4 and 2mM at p!h 6.4. At constant PH., contraction in papillary muscle and the Purkinje fibre proportionalto [a$]? where n is about 3. At constant alal contraction decreases ~~t~HpHi (teyion ~?a?-~ where m is on average, about 2r The quantitative changes . and aNa observe during intracellular acidosrs at pHo 7.4 and 6.4 can be used succe&fully to predict the observed changes in contraction. ?he inotropic response of cardiac muscle to acid-base disturbances therefore depends, in part, on the kinetic properties of Na-H exchange. Supported by a BHF grant to RWJ. s.47
(Supplement
IV)(1988)
1 BUFFER POWER AND INTRACELLULAR pH OF HYPERTROPHIC PAPILLARY MUSCLE FROM FERRET. SBaudet, J.Noireaud, C.Leoty. Laboratory of General Physiology, E.N.V., University of Nantes CP 3013, F-44087 Nantes Cedex 03, France. The development of pressure overload hypertrophy of mammalian myocardium is associated with a decline in contractile function and prolongation of the isometric contraction. These changes may be due to abnormalities in intracellular pH (pHi) handling: this hypothesis has been tested in control ferrets and ferrets in which right ventricular hypertrophy was induced by banding the pulmonary artery. pHi of normal and hypertrophic papillary muscles from ferret heart were measured using pH-sensitive microelectrodes, filled with the ion-exchange resin proton cocktail (Fluka AG). The membrane potential was measured with a separate conventional KCI-filled microelectrode. In HEPES (5mM) buffered Tyrode solution (extracellular pH (pHo) 7.4, 34-36X) mean pHi was similar in the two types of muscles (control: 7.00 +/- 0.13 SD, n=21; hypertrophic: 7.06 +/0.21 SD, n=ll, P>O.l). On changing to Tyrode solution containing CO2 and HC03- (pHo 7.4, 34-36X) pHi became transiently acid in both cardiac tissues. In pathological cells, the calculated buffer power from the changes in pHi was 71.5 mM H+I pH units (+/- 5.0 SEM, n=6). Similar values were obtained in normal cells. Thus changes in the mechanical properties of hypertrophtc cardiac fibres are not due to a difference of pHi or buffering of resting cells. This work was supported by the Fondation myqathies and the Fondation Langlois.
pour
/a Racherche
Mtkiicale.
The Association
Frangaise
contre
/as
P-32 INHIBITION
OF Na-H EXCHANGE IN THE SHEEP CARDIAC PURKINJE FIBRE. M.L.WU a RD.Vaqhan-Jones. University Laboratory of Physiology, Parks Road, Oxford OX1 3PT. Na-H exchange is the principal mechanism regulating pHi in cardiac muscle following an intracellular acid load. We have investigated sOme mechanisms that can lead to inhibition of the exchange. Manoeuvres tpt raise cytoplasmic-s-AMP eg. addition of 25+M 3-isobutyl-l-methyl xanthine, 10 M isoprenaline or 10 M c-AMP slightly inhibit the rate of pH; recovery from an internal acid load (induced bv addition and then removal of 2Om'M NH4Cl) j35&5% inhibition at pHi 6.7, n=8; S.E.M.): Inhibition of aerobic metabolism (5mM CN) slows pH; recovery more effectivelv (5826% inhibition at pHi 6.9, n=lO) whereas inhibitiono? anaerobic metabolism (iOr&2deoxyglucose in glucose-free solution) greatly inhibits pHi-recovery (95&2% inhibition at pH; 6.8, n=4). Although reducino DH: stimulates the exchanaer. reducim pHo inhibits it.lIn two experiments , net acidef&x during pHi recove, was roqhl; equal to k[H+l," where n=O.5 and k depends on PH; (constant Na,). Hence at constant pHi, reducing-pa0 from 7.4-6.4 leads to a70% inhfbition of thgexchanger. Thus two important physiological factors that will affect Na-H exchange are (i) impairment of energy metabolism and (ii) extracellular acidosis. Supported by grants from the Brtish Heart Foundation & N.S.C. of Republic of China.
P-33 INOTROPIC RESPONSESOF MAMMALIAN CARDIAC MUSCLE I0 ACIL0SIS CAN BE PREDICTED FROM THE MEASURED CHANGES IN INTRACELLULAR pH AND SODIUM. R.D.Vaughan-Jones & C.Bountra. University Laboratory of Physiology, Parks Poad,Oxford OX1 3PT. Simultaneous measurement of pHi (ion-selective microelectrode, ISM) and twitch tension in isolated sheep cardiac Purkinje fibres or guinea-pig papillary muscle (HEPES buffered solutions, 100% 02), shows that the inotropic response to acidosis occurs only when there is a change in pH.i. However, a fall in pHi produced by reducing pHo (6.4) results in a negative inotropy, whereas the same fall in pHi produced at a pHo of 7.4 (removal of 1OmM NH Cl) can result in a positive inotropy. These different responses can be explained % y the observation that a fall in pHi raises intracellular Na activity (ai,).via stimulation of Na-H exchange. In papillary muscle, reducing pHi to 7.0 elevates aha (ISM) by about 4mM at pHo 7.4 and 2mM at p!h 6.4. At constant PH., contraction in papillary muscle and the Purkinje fibre proportionalto [a$]? where n is about 3. At constant alal contraction decreases ~~t~HpHi (teyion ~?a?-~ where m is on average, about 2r The quantitative changes . and aNa observe during intracellular acidosrs at pHo 7.4 and 6.4 can be used succe&fully to predict the observed changes in contraction. ?he inotropic response of cardiac muscle to acid-base disturbances therefore depends, in part, on the kinetic properties of Na-H exchange. Supported by a BHF grant to RWJ. s.47