Short-term inhibition of the Na-H exchanger limits acidosis and reduces ischemic injury in the rat heart

Saul Schaefer, Ravichandran Ramasamy

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Pharmacologic inhibition of the Na-H exchanger prior to and during ischemia has been shown to protect the ischemic heart by reducing Na-H exchange. However, pH regulation in the ischemic heart is primarily mediated by other pH regulatory mechanisms, such as metabolite efflux and sodium- coupled HCO3 influx, which may compensate for a reduction in Na-H exchange by increasing proton efflux. We hypothesized that short-term pharmacologic inhibition of the Na-H exchanger would result in increases in other compensatory pH regulatory mechanisms and thereby limit acidosis during ischemia and reduce ischemic injury. Methods: In order to test this hypothesis, we exposed isolated perfused rat hearts to ethylisopropylamiloride (EIPA, 3 μM) for 40 min, followed by 10 min of EIPA- free perfusate and 30 min of global ischemia (termed CTL/EIPA hearts). The effects of this intervention were compared to hearts perfused with either glucose alone (CTL) or EIPA 3 μM for 10 min before ischemia (EIPA). Ischemic injury was measured using creatine kinase (CK) release on reperfusion, while pH and metabolite effects were measured using 31P nuclear magnetic resonance spectroscopy. The effect of this intervention on recovery from an acid load was assessed using an NH4Cl pre-pulse in bicarbonate-containing Krebs-Henseleit as well as HEPES buffer. Results: Both CTLK/EIPA and EIPA hearts had marked reduction in ischemic injury (CK control 1191 ± 116 IU/g dry weight; CTL/EIPA 406 ± 42 IU/gdw; EIPA 333 ± 78 IU/gdw) as well as significantly reduced end-diastolic pressure on reperfusion. Intracellular pH was higher in the CTL/EIPA hearts (end-ischemic pH = 6.34 ± 0.05) compared to either control (5.86 ± 0.02) or EIPA hearts (6.01 ± 0.02), while pH recovery on reperfusion was markedly slowed in the CTL/EIPA hearts. CTL/EIPA hearts had rapid ATP depletion during ischemia, but PCr recovery comparable to EIPA hearts. Acidification on exposure to NH4Cl was increased in the presence of HEPES, but pH recovery was not altered by short-term exposure to EIPA. Conclusions: These data show that short-term inhibition of the Na-H exchanger altered pH regulation in the ischemic heart, resulting in reduced acidosis and slow pH recovery on reperfusion, coupled with reduction in ischemic injury and end-diastolic pressure on reperfusion. These findings are consistent with short-term exposure to EIPA accelerating ATP depletion during ischemia, as well as limiting proton efflux during reperfusion.

Original languageEnglish (US)
Pages (from-to)329-336
Number of pages8
JournalCardiovascular Research
Volume34
Issue number2
DOIs
StatePublished - May 1997

Fingerprint

Sodium-Hydrogen Antiporter
Acidosis
Wounds and Injuries
Reperfusion
Ischemia
HEPES
ethylisopropylamiloride
Creatine Kinase
Protons
Adenosine Triphosphate
Blood Pressure

Keywords

  • Ethylisopropylamiloride
  • Myocardial ischemia
  • Na/H exchange
  • pH
  • Rat, Heart

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine

Cite this

Short-term inhibition of the Na-H exchanger limits acidosis and reduces ischemic injury in the rat heart. / Schaefer, Saul; Ramasamy, Ravichandran.

In: Cardiovascular Research, Vol. 34, No. 2, 05.1997, p. 329-336.

Research output: Contribution to journalArticle

@article{f51b479f6c2341c5a0b9d532daf0ce43,
title = "Short-term inhibition of the Na-H exchanger limits acidosis and reduces ischemic injury in the rat heart",
abstract = "Pharmacologic inhibition of the Na-H exchanger prior to and during ischemia has been shown to protect the ischemic heart by reducing Na-H exchange. However, pH regulation in the ischemic heart is primarily mediated by other pH regulatory mechanisms, such as metabolite efflux and sodium- coupled HCO3 influx, which may compensate for a reduction in Na-H exchange by increasing proton efflux. We hypothesized that short-term pharmacologic inhibition of the Na-H exchanger would result in increases in other compensatory pH regulatory mechanisms and thereby limit acidosis during ischemia and reduce ischemic injury. Methods: In order to test this hypothesis, we exposed isolated perfused rat hearts to ethylisopropylamiloride (EIPA, 3 μM) for 40 min, followed by 10 min of EIPA- free perfusate and 30 min of global ischemia (termed CTL/EIPA hearts). The effects of this intervention were compared to hearts perfused with either glucose alone (CTL) or EIPA 3 μM for 10 min before ischemia (EIPA). Ischemic injury was measured using creatine kinase (CK) release on reperfusion, while pH and metabolite effects were measured using 31P nuclear magnetic resonance spectroscopy. The effect of this intervention on recovery from an acid load was assessed using an NH4Cl pre-pulse in bicarbonate-containing Krebs-Henseleit as well as HEPES buffer. Results: Both CTLK/EIPA and EIPA hearts had marked reduction in ischemic injury (CK control 1191 ± 116 IU/g dry weight; CTL/EIPA 406 ± 42 IU/gdw; EIPA 333 ± 78 IU/gdw) as well as significantly reduced end-diastolic pressure on reperfusion. Intracellular pH was higher in the CTL/EIPA hearts (end-ischemic pH = 6.34 ± 0.05) compared to either control (5.86 ± 0.02) or EIPA hearts (6.01 ± 0.02), while pH recovery on reperfusion was markedly slowed in the CTL/EIPA hearts. CTL/EIPA hearts had rapid ATP depletion during ischemia, but PCr recovery comparable to EIPA hearts. Acidification on exposure to NH4Cl was increased in the presence of HEPES, but pH recovery was not altered by short-term exposure to EIPA. Conclusions: These data show that short-term inhibition of the Na-H exchanger altered pH regulation in the ischemic heart, resulting in reduced acidosis and slow pH recovery on reperfusion, coupled with reduction in ischemic injury and end-diastolic pressure on reperfusion. These findings are consistent with short-term exposure to EIPA accelerating ATP depletion during ischemia, as well as limiting proton efflux during reperfusion.",
keywords = "Ethylisopropylamiloride, Myocardial ischemia, Na/H exchange, pH, Rat, Heart",
author = "Saul Schaefer and Ravichandran Ramasamy",
year = "1997",
month = "5",
doi = "10.1016/S0008-6363(97)00042-4",
language = "English (US)",
volume = "34",
pages = "329--336",
journal = "Cardiovascular Research",
issn = "0008-6363",
publisher = "Oxford University Press",
number = "2",

}

TY - JOUR

T1 - Short-term inhibition of the Na-H exchanger limits acidosis and reduces ischemic injury in the rat heart

AU - Schaefer, Saul

AU - Ramasamy, Ravichandran

PY - 1997/5

Y1 - 1997/5

N2 - Pharmacologic inhibition of the Na-H exchanger prior to and during ischemia has been shown to protect the ischemic heart by reducing Na-H exchange. However, pH regulation in the ischemic heart is primarily mediated by other pH regulatory mechanisms, such as metabolite efflux and sodium- coupled HCO3 influx, which may compensate for a reduction in Na-H exchange by increasing proton efflux. We hypothesized that short-term pharmacologic inhibition of the Na-H exchanger would result in increases in other compensatory pH regulatory mechanisms and thereby limit acidosis during ischemia and reduce ischemic injury. Methods: In order to test this hypothesis, we exposed isolated perfused rat hearts to ethylisopropylamiloride (EIPA, 3 μM) for 40 min, followed by 10 min of EIPA- free perfusate and 30 min of global ischemia (termed CTL/EIPA hearts). The effects of this intervention were compared to hearts perfused with either glucose alone (CTL) or EIPA 3 μM for 10 min before ischemia (EIPA). Ischemic injury was measured using creatine kinase (CK) release on reperfusion, while pH and metabolite effects were measured using 31P nuclear magnetic resonance spectroscopy. The effect of this intervention on recovery from an acid load was assessed using an NH4Cl pre-pulse in bicarbonate-containing Krebs-Henseleit as well as HEPES buffer. Results: Both CTLK/EIPA and EIPA hearts had marked reduction in ischemic injury (CK control 1191 ± 116 IU/g dry weight; CTL/EIPA 406 ± 42 IU/gdw; EIPA 333 ± 78 IU/gdw) as well as significantly reduced end-diastolic pressure on reperfusion. Intracellular pH was higher in the CTL/EIPA hearts (end-ischemic pH = 6.34 ± 0.05) compared to either control (5.86 ± 0.02) or EIPA hearts (6.01 ± 0.02), while pH recovery on reperfusion was markedly slowed in the CTL/EIPA hearts. CTL/EIPA hearts had rapid ATP depletion during ischemia, but PCr recovery comparable to EIPA hearts. Acidification on exposure to NH4Cl was increased in the presence of HEPES, but pH recovery was not altered by short-term exposure to EIPA. Conclusions: These data show that short-term inhibition of the Na-H exchanger altered pH regulation in the ischemic heart, resulting in reduced acidosis and slow pH recovery on reperfusion, coupled with reduction in ischemic injury and end-diastolic pressure on reperfusion. These findings are consistent with short-term exposure to EIPA accelerating ATP depletion during ischemia, as well as limiting proton efflux during reperfusion.

AB - Pharmacologic inhibition of the Na-H exchanger prior to and during ischemia has been shown to protect the ischemic heart by reducing Na-H exchange. However, pH regulation in the ischemic heart is primarily mediated by other pH regulatory mechanisms, such as metabolite efflux and sodium- coupled HCO3 influx, which may compensate for a reduction in Na-H exchange by increasing proton efflux. We hypothesized that short-term pharmacologic inhibition of the Na-H exchanger would result in increases in other compensatory pH regulatory mechanisms and thereby limit acidosis during ischemia and reduce ischemic injury. Methods: In order to test this hypothesis, we exposed isolated perfused rat hearts to ethylisopropylamiloride (EIPA, 3 μM) for 40 min, followed by 10 min of EIPA- free perfusate and 30 min of global ischemia (termed CTL/EIPA hearts). The effects of this intervention were compared to hearts perfused with either glucose alone (CTL) or EIPA 3 μM for 10 min before ischemia (EIPA). Ischemic injury was measured using creatine kinase (CK) release on reperfusion, while pH and metabolite effects were measured using 31P nuclear magnetic resonance spectroscopy. The effect of this intervention on recovery from an acid load was assessed using an NH4Cl pre-pulse in bicarbonate-containing Krebs-Henseleit as well as HEPES buffer. Results: Both CTLK/EIPA and EIPA hearts had marked reduction in ischemic injury (CK control 1191 ± 116 IU/g dry weight; CTL/EIPA 406 ± 42 IU/gdw; EIPA 333 ± 78 IU/gdw) as well as significantly reduced end-diastolic pressure on reperfusion. Intracellular pH was higher in the CTL/EIPA hearts (end-ischemic pH = 6.34 ± 0.05) compared to either control (5.86 ± 0.02) or EIPA hearts (6.01 ± 0.02), while pH recovery on reperfusion was markedly slowed in the CTL/EIPA hearts. CTL/EIPA hearts had rapid ATP depletion during ischemia, but PCr recovery comparable to EIPA hearts. Acidification on exposure to NH4Cl was increased in the presence of HEPES, but pH recovery was not altered by short-term exposure to EIPA. Conclusions: These data show that short-term inhibition of the Na-H exchanger altered pH regulation in the ischemic heart, resulting in reduced acidosis and slow pH recovery on reperfusion, coupled with reduction in ischemic injury and end-diastolic pressure on reperfusion. These findings are consistent with short-term exposure to EIPA accelerating ATP depletion during ischemia, as well as limiting proton efflux during reperfusion.

KW - Ethylisopropylamiloride

KW - Myocardial ischemia

KW - Na/H exchange

KW - pH

KW - Rat, Heart

UR - http://www.scopus.com/inward/record.url?scp=0030947211&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0030947211&partnerID=8YFLogxK

U2 - 10.1016/S0008-6363(97)00042-4

DO - 10.1016/S0008-6363(97)00042-4

M3 - Article

C2 - 9205547

AN - SCOPUS:0030947211

VL - 34

SP - 329

EP - 336

JO - Cardiovascular Research

JF - Cardiovascular Research

SN - 0008-6363

IS - 2

ER -