Abstract
The effects of the thiadiazinone derivative, 5-[1-(3,4-dimethoxybenzoyl)- 1,2,3,4-tetrahydrochinolin-6-yl]-6-methyl-3,6-dihydro-2H-1,3,4-thiadiazin-2- on (EMD 53998), and of its (+)EMD 57033 and (-)EMD 57439 enantiomers, were tested on the contractile properties and cytosolic [Ca2+] ([Ca2+](i)) transients of single intact guinea pig cardiac myocytes. Cells were loaded with the ester form of the fluorescent probe, indo-1, and bathed in a N-2- hydroxyethyl-piperazine-N'-2-ethanesulfonic acid-buffered solution at 25°C (1 mM of CaCl2, 1 Hz stimulation rate). All three substances exerted a pronounced increase in twitch amplitude: the maximal effect of the racemate (380% of control value) was approximately the sum of the effects of its two enantiomers (186 and 236% of control value for the (+)- and (-)-enantiomer, respectively). The [Ca2+](i) transient, measured as the 410-to-490 nm indo- 1 fluorescence ratio transient after excitation, was increased by the racemate and its (-)-enantiomer (172 and 152% of control value, respectively), but was not increased by the (+)-enantiomer. The racemate and the (-)-enantiomer, but not the (+)-enantiomer, markedly reduced the contraction duration and [Ca2+](i) transient duration. In unstimulated cells resting length was significantly reduced by the (+)-enantiomer, and this was accompanied by a decrease in indo-1 fluorescence; the (-)- enantiomer had no effect on either parameter. In the presence of 2,3 butanedione monoxime (BDM), which markedly reduces twitch amplitude by inhibiting cross-bridge mechanics, addition of the (+)-enantiomer restored the twitch contraction to above the pre-BDM level without augmenting the [Ca2+](i) transient. In contrast, the (-)-enantiomer failed to reverse the BDM-induced contractile depression, even though it caused a significant increase of the [Ca2+](i) transient. Thus, in intact cells the positive inotropic effect of EMD 53998 is due to specific properties of its enantiomers: the (-)-enantiomer has adenosine 3',5'-cyclic monophosphate- like effects (increase in amplitude and reduction of [Ca2+](i) transient and contraction durations), whereas the (+)-enantiomer enhances the myofilament-Ca2+ interaction.
| Original language | English |
|---|---|
| Journal | American Journal of Physiology - Heart and Circulatory Physiology |
| Volume | 264 |
| Issue number | 3 33-3 |
| Publication status | Published - 1993 |
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Keywords
- calcium
- contraction
- inotropic agents
- myofilament calcium ion sensitivity
- thiadiazinone derivatives
ASJC Scopus subject areas
- Physiology
Cite this
Enantiomeric dissection of the effects of the inotropic agent, EMD 53998, in single cardiac myocytes. / Gambassi, G.; Capogrossi, M. C.; Klockow, M.; Lakatta, E. G.
In: American Journal of Physiology - Heart and Circulatory Physiology, Vol. 264, No. 3 33-3, 1993.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Enantiomeric dissection of the effects of the inotropic agent, EMD 53998, in single cardiac myocytes
AU - Gambassi, G.
AU - Capogrossi, M. C.
AU - Klockow, M.
AU - Lakatta, E. G.
PY - 1993
Y1 - 1993
N2 - The effects of the thiadiazinone derivative, 5-[1-(3,4-dimethoxybenzoyl)- 1,2,3,4-tetrahydrochinolin-6-yl]-6-methyl-3,6-dihydro-2H-1,3,4-thiadiazin-2- on (EMD 53998), and of its (+)EMD 57033 and (-)EMD 57439 enantiomers, were tested on the contractile properties and cytosolic [Ca2+] ([Ca2+](i)) transients of single intact guinea pig cardiac myocytes. Cells were loaded with the ester form of the fluorescent probe, indo-1, and bathed in a N-2- hydroxyethyl-piperazine-N'-2-ethanesulfonic acid-buffered solution at 25°C (1 mM of CaCl2, 1 Hz stimulation rate). All three substances exerted a pronounced increase in twitch amplitude: the maximal effect of the racemate (380% of control value) was approximately the sum of the effects of its two enantiomers (186 and 236% of control value for the (+)- and (-)-enantiomer, respectively). The [Ca2+](i) transient, measured as the 410-to-490 nm indo- 1 fluorescence ratio transient after excitation, was increased by the racemate and its (-)-enantiomer (172 and 152% of control value, respectively), but was not increased by the (+)-enantiomer. The racemate and the (-)-enantiomer, but not the (+)-enantiomer, markedly reduced the contraction duration and [Ca2+](i) transient duration. In unstimulated cells resting length was significantly reduced by the (+)-enantiomer, and this was accompanied by a decrease in indo-1 fluorescence; the (-)- enantiomer had no effect on either parameter. In the presence of 2,3 butanedione monoxime (BDM), which markedly reduces twitch amplitude by inhibiting cross-bridge mechanics, addition of the (+)-enantiomer restored the twitch contraction to above the pre-BDM level without augmenting the [Ca2+](i) transient. In contrast, the (-)-enantiomer failed to reverse the BDM-induced contractile depression, even though it caused a significant increase of the [Ca2+](i) transient. Thus, in intact cells the positive inotropic effect of EMD 53998 is due to specific properties of its enantiomers: the (-)-enantiomer has adenosine 3',5'-cyclic monophosphate- like effects (increase in amplitude and reduction of [Ca2+](i) transient and contraction durations), whereas the (+)-enantiomer enhances the myofilament-Ca2+ interaction.
AB - The effects of the thiadiazinone derivative, 5-[1-(3,4-dimethoxybenzoyl)- 1,2,3,4-tetrahydrochinolin-6-yl]-6-methyl-3,6-dihydro-2H-1,3,4-thiadiazin-2- on (EMD 53998), and of its (+)EMD 57033 and (-)EMD 57439 enantiomers, were tested on the contractile properties and cytosolic [Ca2+] ([Ca2+](i)) transients of single intact guinea pig cardiac myocytes. Cells were loaded with the ester form of the fluorescent probe, indo-1, and bathed in a N-2- hydroxyethyl-piperazine-N'-2-ethanesulfonic acid-buffered solution at 25°C (1 mM of CaCl2, 1 Hz stimulation rate). All three substances exerted a pronounced increase in twitch amplitude: the maximal effect of the racemate (380% of control value) was approximately the sum of the effects of its two enantiomers (186 and 236% of control value for the (+)- and (-)-enantiomer, respectively). The [Ca2+](i) transient, measured as the 410-to-490 nm indo- 1 fluorescence ratio transient after excitation, was increased by the racemate and its (-)-enantiomer (172 and 152% of control value, respectively), but was not increased by the (+)-enantiomer. The racemate and the (-)-enantiomer, but not the (+)-enantiomer, markedly reduced the contraction duration and [Ca2+](i) transient duration. In unstimulated cells resting length was significantly reduced by the (+)-enantiomer, and this was accompanied by a decrease in indo-1 fluorescence; the (-)- enantiomer had no effect on either parameter. In the presence of 2,3 butanedione monoxime (BDM), which markedly reduces twitch amplitude by inhibiting cross-bridge mechanics, addition of the (+)-enantiomer restored the twitch contraction to above the pre-BDM level without augmenting the [Ca2+](i) transient. In contrast, the (-)-enantiomer failed to reverse the BDM-induced contractile depression, even though it caused a significant increase of the [Ca2+](i) transient. Thus, in intact cells the positive inotropic effect of EMD 53998 is due to specific properties of its enantiomers: the (-)-enantiomer has adenosine 3',5'-cyclic monophosphate- like effects (increase in amplitude and reduction of [Ca2+](i) transient and contraction durations), whereas the (+)-enantiomer enhances the myofilament-Ca2+ interaction.
KW - calcium
KW - contraction
KW - inotropic agents
KW - myofilament calcium ion sensitivity
KW - thiadiazinone derivatives
UR - http://www.scopus.com/inward/record.url?scp=0027513094&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0027513094&partnerID=8YFLogxK
M3 - Article
VL - 264
JO - American Journal of Physiology
JF - American Journal of Physiology
SN - 0363-6119
IS - 3 33-3
ER -