Limits...
Acetate transiently inhibits myocardial contraction by increasing mitochondrial calcium uptake.

Schooley JF, Namboodiri AM, Cox RT, Bünger R, Flagg TP - BMC Physiol. (2014)

Bottom Line: Acute exposure of myocytes to 10 mM sodium acetate caused a marked, but transient, decrease in systolic sarcomere shortening (1.49 ± 0.20% vs. 5.58 ± 0.49% in control), accompanied by a significant increase in diastolic sarcomere length (1.81 ± 0.01 μm vs. 1.77 ± 0.01 μm in control), with a near linear dose response in the 1-10 mM range.Unlike palmitate, acetate caused no change in action potential duration; however, acetate markedly increased mitochondrial Ca(2+) uptake.Lehninger and others have previously demonstrated that the anions of weak aliphatic acids such as acetate stimulate Ca(2+) uptake in isolated mitochondria.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy, Physiology, and Genetics, Uniformed Services University for the Health Sciences, 4301 Jones Bridge Road, Rm. C-2114, Bethesda, 20814, MD, USA. James.Schooley@usuhs.edu.

ABSTRACT

Background: There is a close relationship between cardiovascular disease and cardiac energy metabolism, and we have previously demonstrated that palmitate inhibits myocyte contraction by increasing Kv channel activity and decreasing the action potential duration. Glucose and long chain fatty acids are the major fuel sources supporting cardiac function; however, cardiac myocytes can utilize a variety of substrates for energy generation, and previous studies demonstrate the acetate is rapidly taken up and oxidized by the heart. In this study, we tested the effects of acetate on contractile function of isolated mouse ventricular myocytes.

Results: Acute exposure of myocytes to 10 mM sodium acetate caused a marked, but transient, decrease in systolic sarcomere shortening (1.49 ± 0.20% vs. 5.58 ± 0.49% in control), accompanied by a significant increase in diastolic sarcomere length (1.81 ± 0.01 μm vs. 1.77 ± 0.01 μm in control), with a near linear dose response in the 1-10 mM range. Unlike palmitate, acetate caused no change in action potential duration; however, acetate markedly increased mitochondrial Ca(2+) uptake. Moreover, pretreatment of cells with the mitochondrial Ca(2+) uptake blocker, Ru-360 (10 μM), markedly suppressed the effect of acetate on contraction.

Conclusions: Lehninger and others have previously demonstrated that the anions of weak aliphatic acids such as acetate stimulate Ca(2+) uptake in isolated mitochondria. Here we show that this effect of acetate appears to extend to isolated cardiac myocytes where it transiently modulates cell contraction.

Show MeSH

Related in: MedlinePlus

Thapsigargin pretreatment specifically impairs the recovery of contraction during acetate exposure. (A) Representative recording of average sarcomere length assessed continuously throughout application and removal of normal Tyrode solution (NT) supplemented with 10 mM sodium acetate in cells pretreated with thapsigargin (1 μM) for 2–5 minutes. As expected, cell relaxation was markedly slowed so contractions were evoked at 0.5 Hz. (B & C) Summary data from experiments as in A (n = 9). Thapsigargin pretreatment had no effect on the acetate induced decrease in fractional shortening or increase in diastolic sarcomere length, but markedly blunted the recovery of contraction typically observed from 2–10 minutes during acetate application.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4274725&req=5

Fig6: Thapsigargin pretreatment specifically impairs the recovery of contraction during acetate exposure. (A) Representative recording of average sarcomere length assessed continuously throughout application and removal of normal Tyrode solution (NT) supplemented with 10 mM sodium acetate in cells pretreated with thapsigargin (1 μM) for 2–5 minutes. As expected, cell relaxation was markedly slowed so contractions were evoked at 0.5 Hz. (B & C) Summary data from experiments as in A (n = 9). Thapsigargin pretreatment had no effect on the acetate induced decrease in fractional shortening or increase in diastolic sarcomere length, but markedly blunted the recovery of contraction typically observed from 2–10 minutes during acetate application.

Mentions: The acetate-induced stimulation of mitochondrial Ca2+ uptake appears to be the seminal event leading to reduced inotropy. However, in the sustained presence of acetate, fractional shortening recovers to control levels by 10 minutes. This suggests that during the early phase of acetate exposure, cytosolic Ca2+ released from the SR bypasses the myofilaments and enters the mitochondria. We hypothesized that the recovery of contraction during the latter phase of acetate exposure reflects refilling of the SR to replace the Ca2+ lost to the mitochondria. Previous studies have utilized brief application of 1 μM thapsigargin to partially inhibit SERCA activity [21]. We therefore treated cells with 1 μM thapsigargin for 2–5 minutes prior to transfer to the bath for recording. No thapsigargin was added to the recording solutions. As expected, cell relaxation was markedly slowed by SERCA inhibition and therefore cells were stimulated at 0.5 Hz (instead of 1 Hz) for these experiments (Figure 6). Thapsigargin pretreatment markedly inhibited fractional shortening as expected (Figure 6B, inset), but exposure to acetate still resulted in a decrease in contraction amplitude and increase in diastolic sarcomere length similar to control, untreated cells. It should be noted, however, that the recovery of contraction typically observed during the latter phase of acetate application as well as the transient increase in contraction at washout were not observed in experiments where myocytes were briefly exposed to thapsigargin prior to acetate. This finding suggests that the recovery of contraction during acetate treatment reflects refilling of the sarcomplasmic reticulum with Ca2+.Figure 6


Acetate transiently inhibits myocardial contraction by increasing mitochondrial calcium uptake.

Schooley JF, Namboodiri AM, Cox RT, Bünger R, Flagg TP - BMC Physiol. (2014)

Thapsigargin pretreatment specifically impairs the recovery of contraction during acetate exposure. (A) Representative recording of average sarcomere length assessed continuously throughout application and removal of normal Tyrode solution (NT) supplemented with 10 mM sodium acetate in cells pretreated with thapsigargin (1 μM) for 2–5 minutes. As expected, cell relaxation was markedly slowed so contractions were evoked at 0.5 Hz. (B & C) Summary data from experiments as in A (n = 9). Thapsigargin pretreatment had no effect on the acetate induced decrease in fractional shortening or increase in diastolic sarcomere length, but markedly blunted the recovery of contraction typically observed from 2–10 minutes during acetate application.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4274725&req=5

Fig6: Thapsigargin pretreatment specifically impairs the recovery of contraction during acetate exposure. (A) Representative recording of average sarcomere length assessed continuously throughout application and removal of normal Tyrode solution (NT) supplemented with 10 mM sodium acetate in cells pretreated with thapsigargin (1 μM) for 2–5 minutes. As expected, cell relaxation was markedly slowed so contractions were evoked at 0.5 Hz. (B & C) Summary data from experiments as in A (n = 9). Thapsigargin pretreatment had no effect on the acetate induced decrease in fractional shortening or increase in diastolic sarcomere length, but markedly blunted the recovery of contraction typically observed from 2–10 minutes during acetate application.
Mentions: The acetate-induced stimulation of mitochondrial Ca2+ uptake appears to be the seminal event leading to reduced inotropy. However, in the sustained presence of acetate, fractional shortening recovers to control levels by 10 minutes. This suggests that during the early phase of acetate exposure, cytosolic Ca2+ released from the SR bypasses the myofilaments and enters the mitochondria. We hypothesized that the recovery of contraction during the latter phase of acetate exposure reflects refilling of the SR to replace the Ca2+ lost to the mitochondria. Previous studies have utilized brief application of 1 μM thapsigargin to partially inhibit SERCA activity [21]. We therefore treated cells with 1 μM thapsigargin for 2–5 minutes prior to transfer to the bath for recording. No thapsigargin was added to the recording solutions. As expected, cell relaxation was markedly slowed by SERCA inhibition and therefore cells were stimulated at 0.5 Hz (instead of 1 Hz) for these experiments (Figure 6). Thapsigargin pretreatment markedly inhibited fractional shortening as expected (Figure 6B, inset), but exposure to acetate still resulted in a decrease in contraction amplitude and increase in diastolic sarcomere length similar to control, untreated cells. It should be noted, however, that the recovery of contraction typically observed during the latter phase of acetate application as well as the transient increase in contraction at washout were not observed in experiments where myocytes were briefly exposed to thapsigargin prior to acetate. This finding suggests that the recovery of contraction during acetate treatment reflects refilling of the sarcomplasmic reticulum with Ca2+.Figure 6

Bottom Line: Acute exposure of myocytes to 10 mM sodium acetate caused a marked, but transient, decrease in systolic sarcomere shortening (1.49 ± 0.20% vs. 5.58 ± 0.49% in control), accompanied by a significant increase in diastolic sarcomere length (1.81 ± 0.01 μm vs. 1.77 ± 0.01 μm in control), with a near linear dose response in the 1-10 mM range.Unlike palmitate, acetate caused no change in action potential duration; however, acetate markedly increased mitochondrial Ca(2+) uptake.Lehninger and others have previously demonstrated that the anions of weak aliphatic acids such as acetate stimulate Ca(2+) uptake in isolated mitochondria.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy, Physiology, and Genetics, Uniformed Services University for the Health Sciences, 4301 Jones Bridge Road, Rm. C-2114, Bethesda, 20814, MD, USA. James.Schooley@usuhs.edu.

ABSTRACT

Background: There is a close relationship between cardiovascular disease and cardiac energy metabolism, and we have previously demonstrated that palmitate inhibits myocyte contraction by increasing Kv channel activity and decreasing the action potential duration. Glucose and long chain fatty acids are the major fuel sources supporting cardiac function; however, cardiac myocytes can utilize a variety of substrates for energy generation, and previous studies demonstrate the acetate is rapidly taken up and oxidized by the heart. In this study, we tested the effects of acetate on contractile function of isolated mouse ventricular myocytes.

Results: Acute exposure of myocytes to 10 mM sodium acetate caused a marked, but transient, decrease in systolic sarcomere shortening (1.49 ± 0.20% vs. 5.58 ± 0.49% in control), accompanied by a significant increase in diastolic sarcomere length (1.81 ± 0.01 μm vs. 1.77 ± 0.01 μm in control), with a near linear dose response in the 1-10 mM range. Unlike palmitate, acetate caused no change in action potential duration; however, acetate markedly increased mitochondrial Ca(2+) uptake. Moreover, pretreatment of cells with the mitochondrial Ca(2+) uptake blocker, Ru-360 (10 μM), markedly suppressed the effect of acetate on contraction.

Conclusions: Lehninger and others have previously demonstrated that the anions of weak aliphatic acids such as acetate stimulate Ca(2+) uptake in isolated mitochondria. Here we show that this effect of acetate appears to extend to isolated cardiac myocytes where it transiently modulates cell contraction.

Show MeSH
Related in: MedlinePlus