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Effect of norepinephrine on mitochondrial calcium in rat myocytes
J Mol Cell Cardiol23 (Supplement III) (1991)
.4-11 STIMULATION Pm
OF 6 OPIOID RECEPTORS IN SINGLE HEART CELLS BLOCKS /I-ADRENERGIC RECEPTOR MEDIATED INCREASE IN CALCIUM AND CONTRACTION &~&&&QQ, Maurizio C Capogrossi, Harold A Spurgeon, Edward G Lakatta. Gerontology Research Center, National Institute of Aging, NIH, Baltimore, MD 21224 US.A. Whether stimulation of myocardial opioid (OP) receptors modifies the response to @adrenergic receptor (BAR) stimulation is unknown. In individual isolated rat ventricular myocytes (electrically stimulated at 0.5 Hz at 23°C) we find that the increase in cytosolic Ca’+ (indexed by indo-l transient fluorescence) and contraction (measured via photodiode array) amplitudes in response to norepinephrine (NE,lO-‘M) are abolished by the addition of lo-‘M Leucine enkephalin (LE), a 6 OP agonist (fig). The LE effect is reversed by Naloxone (Nal,lO-‘M). Thus, stimulation of 6 OP receptors on heart cells can “short circuit” the BAR mediated response and may protect against cell Ca’+ overload during stress.
P-4-l 2 EFFECT OF NOREPINEPHRINE
ON MITOCHONDRIAL CALCIUM IN RAT MYOCYTES Haruo Miyata, Howard Silverman Michael D. Stern Richard G. Hansford, Edward G. Lakatta. Gerontology Research Center, National Institute on Aging, NIH, Baltimore, MD 21224 USA It has not previously been possible to measure mitochondrial Ca” ([Ca’+]3 in living myocytes. Contraction and Indo-l fluorescence are measured simultaneously in single rat ventricular cells loaded with Indo-l AM and stimulated at 0.2Hz at 23°C. Upon quenching of the cytosolic fluorescence by Mn” (lOO~M), no fluorescence transient accompanies the twitch (Fig2 and the residual Indo-l fluorescence reflects [Ca ‘I,; subsequent augmentation of the twitch by norepinephrine (1 pM) is accompanied by a steady increase in [Ca”], (8355 nM to 111+20 nM, n=4). Increasing the stimulation to 4Hz (not shown) caused a greater increase in [Ca”‘],, to 410285nM. These results are consistent with a role of [Ca”], in activating oxidative phosphorylation.
P-4-13
INTRACELLULAR [Na+] REOXYGRNATION Mark C Haigney, Haruo Gerontology Research Baltimore,
MD
CHANGES Miyata, Center,
IN Edward NIA,
RAT
CARDIAC
G Lakatta, NIH and
HYOCYTRS
EXPOSED
TO
Michael D Stern, Howard Johns Hopkins Medical
HYPOXIA
AND
S Silverman. Institutions,
21205.
Intracellular ionized Na+ ([Na+li) was monitored in single adult rat cardiac myocytes exposed to glucose-free hypoxia (pO2<.02 torr) and reoxygenated 30 minutes after the onset of hypoxic rigor contracture (R). Cells loaded with the fluorescent sodium probe SBFI (excitation ratio 350/380 ran), stimulated at 0.2 HZ demonstrated a mild initial increase in fluorescence ratio following the onset of hypoxia and a further progressive and marked rise after the onset of 1.2 rigor (T=37OC, buffer [Na+]=137 au4, n=5). At g 1.1 reoxygenation these changes rapidly reversed (figure, c 1 open circles). A separate group of cells (n=3) were 5: @Y 0.9 exposed to hypoxia in a buffer containing no Na+ and these showed minor cells only changes in SBFI Q 0.8 fluorescence ratio (figure, closed circles). Hence [Na+li 2 0.7 markedly increases in cells following profound energy [r 0.6 depletion (rigor) as a result of sodium entry into cells TIME rather than intracellular shifts in Na+.
5.83
.4-11 STIMULATION Pm
OF 6 OPIOID RECEPTORS IN SINGLE HEART CELLS BLOCKS /I-ADRENERGIC RECEPTOR MEDIATED INCREASE IN CALCIUM AND CONTRACTION &~&&&QQ, Maurizio C Capogrossi, Harold A Spurgeon, Edward G Lakatta. Gerontology Research Center, National Institute of Aging, NIH, Baltimore, MD 21224 US.A. Whether stimulation of myocardial opioid (OP) receptors modifies the response to @adrenergic receptor (BAR) stimulation is unknown. In individual isolated rat ventricular myocytes (electrically stimulated at 0.5 Hz at 23°C) we find that the increase in cytosolic Ca’+ (indexed by indo-l transient fluorescence) and contraction (measured via photodiode array) amplitudes in response to norepinephrine (NE,lO-‘M) are abolished by the addition of lo-‘M Leucine enkephalin (LE), a 6 OP agonist (fig). The LE effect is reversed by Naloxone (Nal,lO-‘M). Thus, stimulation of 6 OP receptors on heart cells can “short circuit” the BAR mediated response and may protect against cell Ca’+ overload during stress.
P-4-l 2 EFFECT OF NOREPINEPHRINE
ON MITOCHONDRIAL CALCIUM IN RAT MYOCYTES Haruo Miyata, Howard Silverman Michael D. Stern Richard G. Hansford, Edward G. Lakatta. Gerontology Research Center, National Institute on Aging, NIH, Baltimore, MD 21224 USA It has not previously been possible to measure mitochondrial Ca” ([Ca’+]3 in living myocytes. Contraction and Indo-l fluorescence are measured simultaneously in single rat ventricular cells loaded with Indo-l AM and stimulated at 0.2Hz at 23°C. Upon quenching of the cytosolic fluorescence by Mn” (lOO~M), no fluorescence transient accompanies the twitch (Fig2 and the residual Indo-l fluorescence reflects [Ca ‘I,; subsequent augmentation of the twitch by norepinephrine (1 pM) is accompanied by a steady increase in [Ca”], (8355 nM to 111+20 nM, n=4). Increasing the stimulation to 4Hz (not shown) caused a greater increase in [Ca”‘],, to 410285nM. These results are consistent with a role of [Ca”], in activating oxidative phosphorylation.
P-4-13
INTRACELLULAR [Na+] REOXYGRNATION Mark C Haigney, Haruo Gerontology Research Baltimore,
MD
CHANGES Miyata, Center,
IN Edward NIA,
RAT
CARDIAC
G Lakatta, NIH and
HYOCYTRS
EXPOSED
TO
Michael D Stern, Howard Johns Hopkins Medical
HYPOXIA
AND
S Silverman. Institutions,
21205.
Intracellular ionized Na+ ([Na+li) was monitored in single adult rat cardiac myocytes exposed to glucose-free hypoxia (pO2<.02 torr) and reoxygenated 30 minutes after the onset of hypoxic rigor contracture (R). Cells loaded with the fluorescent sodium probe SBFI (excitation ratio 350/380 ran), stimulated at 0.2 HZ demonstrated a mild initial increase in fluorescence ratio following the onset of hypoxia and a further progressive and marked rise after the onset of 1.2 rigor (T=37OC, buffer [Na+]=137 au4, n=5). At g 1.1 reoxygenation these changes rapidly reversed (figure, c 1 open circles). A separate group of cells (n=3) were 5: @Y 0.9 exposed to hypoxia in a buffer containing no Na+ and these showed minor cells only changes in SBFI Q 0.8 fluorescence ratio (figure, closed circles). Hence [Na+li 2 0.7 markedly increases in cells following profound energy [r 0.6 depletion (rigor) as a result of sodium entry into cells TIME rather than intracellular shifts in Na+.
5.83