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Inhibition of ion channels and heart beat in Drosophila by selective COX-2 inhibitor SC-791.

Frolov RV, Singh S - PLoS ONE (2012)

Bottom Line: To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human K(v)2.1 channels by a highly selective COX-2 inhibitor SC-791.Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K(+) and L-type Ca(2+) channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner.Unlike celecoxib and several other K(+) channel blockers, SC-791 did not induce arrhythmia.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Toxicology, State University of New York at Buffalo, Buffalo, New York, United States of America. rvfrolov@gmail.com

ABSTRACT
Recent findings suggest that modulation of ion channels might be implicated in some of the clinical effects of coxibs, selective inhibitors of cyclooxygenase-2 (COX-2). Celecoxib and its inactive analog 2,5-dimethyl-celecoxib, but not rofecoxib, can suppress or augment ionic currents and alter functioning of neurons and myocytes. To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human K(v)2.1 channels by a highly selective COX-2 inhibitor SC-791. In this study we have further explored the SC-791 action on ion channels and heartbeat in Drosophila, which lacks cyclooxygenases and thus can serve as a convenient model to study COX-2-independent mechanisms of coxibs. Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K(+) and L-type Ca(2+) channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner. Unlike celecoxib and several other K(+) channel blockers, SC-791 did not induce arrhythmia. Instead, application of SC-791 resulted in a dramatic slowing of contractions and, at higher concentrations, in progressively weaker contractions with gradual cessation of heartbeat. Isradipine, a selective blocker of L-type Ca(2+) channels, showed a similar pattern of heart arrest, though no prolongation of contractions was observed. Ryanodine was the only channel modulating compound of those tested additionally that was capable of slowing contractions. Like SC-791, ryanodine reduced heart rate without arrhythmia. However, it could not stop heartbeat completely even at 500 µM, the highest concentration used. The magnitude of heart rate reduction, when SC-791 and ryanodine were applied together, was smaller than expected for independent mechanisms, raising the possibility that SC-791 might be interfering with excitation-contraction coupling in Drosophila heart.

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Effects of ryanodine on heartbeat.Typical examples of heartbeat in control, after 20 min application of either 100 µM ryanodine (A) or 30 µM SC-791 (B) alone followed by 20 min exposure to a solution containing both 100 µM ryanodine and 30 µM SC-791, and after the wash-out. (C, D) Time course of the average heart rate in the experiments described in the panels (A) and (B), respectively; dotted lines indicate the value of BIC (82% heart rate inhibition) (see Results); panels (C) and (D), averages of 7 and 6 experiments, respectively. (E) Bar plot illustrates differences between the BIC of 0.82 and the experimentally determined total fractional reduction in heart rate for three experimental conditions: when SC-791/ryanodine was applied after (1) exposure to ryanodine alone, (2) exposure to SC-791 alone, and (3) without pre-exposure of the preparation to any compound. (F) Bar plot summarizes effects of ryanodine and SC-791 on the duration of heart contraction when the chemicals were applied in different order as in the panels (A) and (B).
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pone-0038759-g005: Effects of ryanodine on heartbeat.Typical examples of heartbeat in control, after 20 min application of either 100 µM ryanodine (A) or 30 µM SC-791 (B) alone followed by 20 min exposure to a solution containing both 100 µM ryanodine and 30 µM SC-791, and after the wash-out. (C, D) Time course of the average heart rate in the experiments described in the panels (A) and (B), respectively; dotted lines indicate the value of BIC (82% heart rate inhibition) (see Results); panels (C) and (D), averages of 7 and 6 experiments, respectively. (E) Bar plot illustrates differences between the BIC of 0.82 and the experimentally determined total fractional reduction in heart rate for three experimental conditions: when SC-791/ryanodine was applied after (1) exposure to ryanodine alone, (2) exposure to SC-791 alone, and (3) without pre-exposure of the preparation to any compound. (F) Bar plot summarizes effects of ryanodine and SC-791 on the duration of heart contraction when the chemicals were applied in different order as in the panels (A) and (B).

Mentions: Ryanodine is a highly selective modulator of the RyR Ca2+ release channels. At nanomolar concentrations ryanodine promotes opening of the RyR, at low micromolar concentrations it locks the RyR in the half-open state, and at concentrations around 100 μM it completely and irreversibly inhibits the RyR [30]. In our experiments, 100 μM ryanodine instantly and irreversibly reduced heart rate with a remarkable prolongation of contractions (Fig. 5A). Interestingly, 10, 100, and 500 µM ryanodine reduced heartbeat to a similar degree, by 61±4, 62±2, and 63±5%, respectively, suggesting that all these concentrations are in the saturation range. As even 500 μM ryanodine, the highest concentration used, could not stop heartbeat, these results also indicated that RyR-mediated Ca2+ release is an important but not the essential aspect of EC coupling in the larval heart. This conclusion is consistent with the previously published observations [30].


Inhibition of ion channels and heart beat in Drosophila by selective COX-2 inhibitor SC-791.

Frolov RV, Singh S - PLoS ONE (2012)

Effects of ryanodine on heartbeat.Typical examples of heartbeat in control, after 20 min application of either 100 µM ryanodine (A) or 30 µM SC-791 (B) alone followed by 20 min exposure to a solution containing both 100 µM ryanodine and 30 µM SC-791, and after the wash-out. (C, D) Time course of the average heart rate in the experiments described in the panels (A) and (B), respectively; dotted lines indicate the value of BIC (82% heart rate inhibition) (see Results); panels (C) and (D), averages of 7 and 6 experiments, respectively. (E) Bar plot illustrates differences between the BIC of 0.82 and the experimentally determined total fractional reduction in heart rate for three experimental conditions: when SC-791/ryanodine was applied after (1) exposure to ryanodine alone, (2) exposure to SC-791 alone, and (3) without pre-exposure of the preparation to any compound. (F) Bar plot summarizes effects of ryanodine and SC-791 on the duration of heart contraction when the chemicals were applied in different order as in the panels (A) and (B).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3368905&req=5

pone-0038759-g005: Effects of ryanodine on heartbeat.Typical examples of heartbeat in control, after 20 min application of either 100 µM ryanodine (A) or 30 µM SC-791 (B) alone followed by 20 min exposure to a solution containing both 100 µM ryanodine and 30 µM SC-791, and after the wash-out. (C, D) Time course of the average heart rate in the experiments described in the panels (A) and (B), respectively; dotted lines indicate the value of BIC (82% heart rate inhibition) (see Results); panels (C) and (D), averages of 7 and 6 experiments, respectively. (E) Bar plot illustrates differences between the BIC of 0.82 and the experimentally determined total fractional reduction in heart rate for three experimental conditions: when SC-791/ryanodine was applied after (1) exposure to ryanodine alone, (2) exposure to SC-791 alone, and (3) without pre-exposure of the preparation to any compound. (F) Bar plot summarizes effects of ryanodine and SC-791 on the duration of heart contraction when the chemicals were applied in different order as in the panels (A) and (B).
Mentions: Ryanodine is a highly selective modulator of the RyR Ca2+ release channels. At nanomolar concentrations ryanodine promotes opening of the RyR, at low micromolar concentrations it locks the RyR in the half-open state, and at concentrations around 100 μM it completely and irreversibly inhibits the RyR [30]. In our experiments, 100 μM ryanodine instantly and irreversibly reduced heart rate with a remarkable prolongation of contractions (Fig. 5A). Interestingly, 10, 100, and 500 µM ryanodine reduced heartbeat to a similar degree, by 61±4, 62±2, and 63±5%, respectively, suggesting that all these concentrations are in the saturation range. As even 500 μM ryanodine, the highest concentration used, could not stop heartbeat, these results also indicated that RyR-mediated Ca2+ release is an important but not the essential aspect of EC coupling in the larval heart. This conclusion is consistent with the previously published observations [30].

Bottom Line: To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human K(v)2.1 channels by a highly selective COX-2 inhibitor SC-791.Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K(+) and L-type Ca(2+) channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner.Unlike celecoxib and several other K(+) channel blockers, SC-791 did not induce arrhythmia.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Toxicology, State University of New York at Buffalo, Buffalo, New York, United States of America. rvfrolov@gmail.com

ABSTRACT
Recent findings suggest that modulation of ion channels might be implicated in some of the clinical effects of coxibs, selective inhibitors of cyclooxygenase-2 (COX-2). Celecoxib and its inactive analog 2,5-dimethyl-celecoxib, but not rofecoxib, can suppress or augment ionic currents and alter functioning of neurons and myocytes. To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human K(v)2.1 channels by a highly selective COX-2 inhibitor SC-791. In this study we have further explored the SC-791 action on ion channels and heartbeat in Drosophila, which lacks cyclooxygenases and thus can serve as a convenient model to study COX-2-independent mechanisms of coxibs. Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K(+) and L-type Ca(2+) channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner. Unlike celecoxib and several other K(+) channel blockers, SC-791 did not induce arrhythmia. Instead, application of SC-791 resulted in a dramatic slowing of contractions and, at higher concentrations, in progressively weaker contractions with gradual cessation of heartbeat. Isradipine, a selective blocker of L-type Ca(2+) channels, showed a similar pattern of heart arrest, though no prolongation of contractions was observed. Ryanodine was the only channel modulating compound of those tested additionally that was capable of slowing contractions. Like SC-791, ryanodine reduced heart rate without arrhythmia. However, it could not stop heartbeat completely even at 500 µM, the highest concentration used. The magnitude of heart rate reduction, when SC-791 and ryanodine were applied together, was smaller than expected for independent mechanisms, raising the possibility that SC-791 might be interfering with excitation-contraction coupling in Drosophila heart.

Show MeSH
Related in: MedlinePlus