Srinivasan G. Varadarajan

Sevoflurane before or after Ischemia Improves Contractile and Metabolic Function while Reducing Myoplasmic Ca2+Loading in Intact Hearts

Background Ca2+ loading occurs during myocardial reperfusion injury. Volatile anesthetics can reduce reperfusion injury. The authors tested whether sevoflurane administered before index ischemia in isolated hearts reduces myoplasmic diastolic and systolic [Ca2+] and improves function more so than when sevoflurane is administered on reperfusion. Methods Four groups of guinea pig hearts were perfused with crystalloid solution (55 mmHg, 37°C): (1) no treatment before 30 min global ischemia and 60 min reperfusion (CON); (2) 3.5 vol% sevoflurane administered for 10 min before ischemia (SBI); (3) 3.5 vol% sevoflurane administered for 10 min after ischemia (SAI); and (4) 3.5 vol% sevoflurane administered for 10 min before and after ischemia (SBAI). Phasic myoplasmic diastolic and systolic [Ca2+] were measured in the left ventricular free wall with the fluorescence probe indo-1. Results Ischemia increased diastolic [Ca2+] and diastolic left ventricular pressure (LVP). In CON hearts, initial reperfusion greatly increased diastolic [Ca2+] and systolic [Ca2+] and reduced contractility (systolic–diastolic LVP, dLVP/dtmax), relaxation (diastolic LVP, dLVP/dtmin), myocardial oxygen consumption (Mvo2), and cardiac efficiency. SBI, SAI, and SBAI each reduced ventricular fibrillation, attenuated increases in systolic and systolic–diastolic [Ca2+], improved contractile and relaxation indices, and increased coronary flow, percent oxygen extraction, Mvo2, and cardiac efficiency during 60 min reperfusion compared with CON. SBI was more protective than SAI, and SBAI was generally more protective than SAI. Conclusions Sevoflurane improves postischemic cardiac function while reducing Ca2+ loading when it is administered before or after ischemia, but protection is better when it is administered before ischemia. Reduced Ca2+ loading on reperfusion is likely a result of the anesthetic protective effect.

Modulation of myocardial function and [Ca2+] sensitivity by moderate hypothermia in guinea pig isolated hearts

Cardiac hypothermia alters contractility and intracellular Ca2+ concentration ([Ca2+]i) homeostasis. We examined how left ventricular pressure (LVP) is altered as a function of cytosolic [Ca2+]iover a range of extracellular CaCl2 concentration ([CaCl2]e) during perfusion of isolated, paced guinea pig hearts at 37°C, 27°C, and 17°C. Transmural LV phasic [Ca2+] was measured using the Ca2+ indicator indo 1 and calibrated (in nM) after correction was made for autofluorescence, temperature, and noncytosolic Ca2+. Noncytosolic [Ca2+]i, cytosolic diastolic and systolic [Ca2+]i, phasic [Ca2+]i, and systolic Ca2+ released per beat (area Ca2+) were plotted as a function of 0.3-4.5 mM [CaCl2]e, and indexes of contractility [LVP, maximal rates of LVP development (+dLVP/d t) and relaxation (-dLVP/d t), and the integral of the LVP curve per beat (LVParea)] were plotted as a function of [Ca2+]i. Hypothermia increased systolic [Ca2+]iand slightly changed systolic LVP but increased diastolic LVP and [Ca2+]i. The relationship of diastolic and noncytosolic [Ca2+] to [CaCl2]ewas shifted upward at 17°C and 27°C, whereas that of phasic [Ca2+]ito [CaCl2]ewas shifted upward at 17°C but not at 27°C. The relationships of phasic [Ca2+]ito developed LVP, +dLVP/d t, and LVParea were progressively reduced by hypothermia so that maximal Ca2+-activated LVP decreased and hearts were desensitized to Ca2+. Thus mild hypothermia modestly increases diastolic and noncytosolic Ca2+ with little effect on systolic Ca2+ or released (area) Ca2+, whereas moderate hypothermia markedly increases diastolic, noncytosolic, peak systolic, and released Ca2+ and results in reduced maximal Ca2+-activated LVP and myocardial sensitivity to systolic Ca2+.Cardiac hypothermia alters contractility and intracellular Ca2+ concentration ([Ca2+]i) homeostasis. We examined how left ventricular pressure (LVP) is altered as a function of cytosolic [Ca2+]i over a range of extracellular CaCl2 concentration ([CaCl2]e) during perfusion of isolated, paced guinea pig hearts at 37 degrees C, 27 degrees C, and 17 degrees C. Transmural LV phasic [Ca2+] was measured using the Ca2+ indicator indo 1 and calibrated (in nM) after correction was made for autofluorescence, temperature, and noncytosolic Ca2+. Noncytosolic [Ca2+]i, cytosolic diastolic and systolic [Ca2+]i, phasic [Ca2+]i, and systolic Ca2+ released per beat (area Ca2+) were plotted as a function of 0.3-4.5 mM [CaCl2]e, and indexes of contractility [LVP, maximal rates of LVP development (+dLVP/dt) and relaxation (-dLVP/dt), and the integral of the LVP curve per beat (LVParea)] were plotted as a function of [Ca2+]i. Hypothermia increased systolic [Ca2+]i and slightly changed systolic LVP but increased diastolic LVP and [Ca2+]i. The relationship of diastolic and noncytosolic [Ca2+] to [CaCl2]e was shifted upward at 17 degrees C and 27 degrees C, whereas that of phasic [Ca2+]) to [CaCl2]e was shifted upward at 17 degrees C but not at 27 degrees C. The relationships of phasic [Ca2+]i to developed LVP, +dLVP/dt, and LVP(area) were progressively reduced by hypothermia so that maximal Ca2+-activated LVP decreased and hearts were desensitized to Ca2+. Thus mild hypothermia modestly increases diastolic and noncytosolic Ca2+ with little effect on systolic Ca2+ or released (area) Ca2+, whereas moderate hypothermia markedly increases diastolic, noncytosolic, peak systolic, and released Ca2+ and results in reduced maximal Ca2+-activated LVP and myocardial sensitivity to systolic Ca2+.

Reduced Cytosolic Ca2+ Loading and Improved Cardiac Function After Cardioplegic Cold Storage of Guinea Pig Isolated Hearts

BackgroundHypothermia is cardioprotective, but it causes Ca2+ loading and reduced function on rewarming. The aim was to associate changes in cytosolic Ca2+ with function in intact hearts before, during, and after cold storage with or without cardioplegia (CP). Methods and ResultsGuinea pig hearts were initially perfused at 37°C with Krebs-Ringer’s (KR) solution (in mmol/L: Ca2+ 2.5, K+ 5, Mg2+ 2.4). One group was perfused with CP solution (Ca2+ 2.5, K+ 18, Mg2+ 7.2) during cooling and storage at 3°C for 4 hours; another was perfused with KR. LV pressure (LVP), dP/dt, O2 consumption, and cardiac efficiency were monitored. Cytosolic phasic [Ca2+] was calculated from indo 1 fluorescence signals obtained at the LV free wall. Cooling with KR increased diastolic and phasic [Ca2+], whereas cooling with CP suppressed phasic [Ca2+] and reduced the rise in diastolic [Ca2+]. Reperfusion with warm KR increased phasic [Ca2+] 86% more after CP at 20 minutes and did not increase diastolic [Ca2+] at 60 minutes, compared with a 20% increase in phasic [Ca2+] after KR. During early and later reperfusion after CP, there was a 126% and 50% better return of LVP than after KR; during later reperfusion, O2 consumption was 23% higher and cardiac efficiency was 38% higher after CP than after KR. ConclusionsCP decreases the rise in cardiac diastolic [Ca2+] observed during cold storage in KR. Decreased diastolic [Ca2+] and increased systolic [Ca2+] after CP improves function on reperfusion because of reduced Ca2+ loading during and immediately after cold CP storage.

Na+/H+ exchange inhibition with cardioplegia reduces cytosolic [Ca2+] and myocardial damage after cold ischemia.

Cold cardioplegia protects against reperfusion damage. Blocking Na+/H+ exchange may be as protective as cardioplegia by improving the left ventricular pressure (LVP)-[Ca2+] relationship after cold ischemia. In guinea pig isolated hearts subjected to cold ischemia (4 h, 17°C) and reperfusion, the cardioprotective effects of a Krebs-Ringer (KR) solution, a cardioplegia solution, a KR solution containing the Na+/H+ exchange inhibitor eniporide (1 &mgr;M), and a cardioplegia solution containing eniporide were compared. Treatments were given before and initially after cold ischemia. Systolic and diastolic [Ca2+] were calculated from indo-1 fluorescence transients recorded at the LV free wall. During ischemia, diastolic [Ca2+] increased in each group but more so in the KR group. Peak systolic and diastolic [Ca2+] on initial reperfusion were highest after KR and smallest after cardioplegia + eniporide. After reperfusion, systolic-diastolic LVP (% of baseline) and infarct size (%), respectively, were KR, 47 ± 3%, 37 ± 4%; cardioplegia, 71 ± 5%*, 20 ± 2.2%*; KR + eniporide, 73 ± 5%*, 11 ± 3%*†; and cardioplegia + eniporide 77 ± 3%*, 10 ± 1.4%*† (* P ≤ 0.05 vs KR; †P ≤ 0.05 vs cardioplegia). Ca2+ overload was reduced in each treated group, and most in the cardioplegia + eniporide group, and was associated with the improved function. Inhibition of Na+/H+ exchange was as effective as cardioplegia in restoring function and better than cardioplegia in reducing infarct size after hypothermic ischemia. The combination of cardioplegia and Na+/H+ exchange inhibition did not produce additive protective effects but caused a larger decrease in Ca2+ loading.

Inhibition of Na+/H+ isoform-1 exchange protects hearts perfused after 6-hour cardioplegic cold storage

OBJECTIVES Cardiac ischemia-reperfusion activates Na(+)/H(+) exchange; excess Na(+) and the resulting Ca(2+) overload, through reverse Na(+)/Ca(2+) exchange, cause cellular injury and cardiac dysfunction. We postulated that inhibiting the Na(+)/H(+) isoform-1 exchanger would add to the protection of hearts after long-term cold storage in acidic cardioplegic solution. METHODS Guinea pig hearts were isolated and perfused at 37 degrees C with Krebs-Ringers solution (KRS) and then switched to an acidic St. Thomas solution (STS) at 25 degrees C. Perfusion was stopped at 10 degrees C, and hearts were stored for 6 hours in STS at 3.4 degrees C. On reperfusion to 25 degrees C, hearts were perfused with KRS for 60 minutes. Hearts were divided into 4 groups: sham control (SHAM); eniporide (EPR, EMD96785) IV, 1 mg/kg given IV over 15 minutes before heart isolation; EPR intracoronary, 1 micromol/liter in STS given intracoronary after heart isolation; and EPR IV and intracoronary. RESULTS Values at 60 minutes reperfusion (the percentage of control [100%] before cold storage) are given, respectively, for EPR IV, EPR intracoronary, and EPR IV and intracoronary vs drug-free SHAM (SEM, *p < 0.05 vs SHAM): 72% +/- 3%*, 65% +/- 3%*, and 81% +/- 2%* vs 55% +/- 3% for left ventricular pressure; 94% +/- 3%*, 96% +/- 5%*, and 102% +/- 2%* vs 81% +/- 3% for coronary flow; 60% +/- 2%, 58% +/- 3%, and 74%* +/- 3% vs 58% +/- 4% for cardiac efficiency; 106% +/- 2%*, 108% +/- 3%*, and 107% +/- 2%* vs 116% +/- 4% for percentage of O(2) extraction. Infarct size as percentage of ventricular weight was 20% +/- 3%*, 31% +/- 3%, and 6% +/- 2%* vs 35% +/- 3% (SHAM) after 60 minutes of reperfusion. CONCLUSIONS Na(+)/H(+) isoform-1 exchanger inhibition, particularly if given IV before storage and intracoronary during cooling and rewarming, adds to the protection of cardioplegic solutions.

Improved mitochondrial bioenergetics by anesthetic preconditioning during and after 2 hours of 27°C ischemia in isolated hearts

We examined if sevoflurane given before cold ischemia of intact hearts (anesthetic preconditioning, APC) affords additional protection by further improving mitochondrial energy balance and if this is abolished by a mitochondrial KATP blocker. NADH and FAD fluorescence was measured within the left ventricular wall of 5 groups of isolated guinea pig hearts: (1) hypothermia alone; (2) hypothermia + ischemia; (3) APC (4.1% sevoflurane) + cold ischemia; (4) 5-HD + cold ischemia, and (5) APC + 5-HD + cold ischemia. Hearts were exposed to sevoflurane for 15 minutes followed by 15 minutes of washout at 37°C before cooling, 2 hours of 27°C ischemia, and 2 hours of 37°C reperfusion. The KATP channel inhibitor 5-HD was perfused before and after sevoflurane. Ischemia caused a rapid increase in NADH and a decrease in FAD that waned over 2 hours. Warm reperfusion led to a decrease in NADH and an increase in FAD. APC attenuated the changes in NADH and FAD and further improved postischemic function and reduced infarct size. 5-HD blocked the cardioprotective effects of APC but not APC-induced alterations of NADH and FAD. Thus, APC improves redox balance and has additive cardioprotective effects with mild hypothermic ischemia. 5-HD blocks APC-induced cardioprotective effects but not improvements in mitochondrial bioenergetics. This suggests that mediation of protection by KATP channel opening during cold ischemia and reperfusion is downstream from the APC-induced improvement in redox state or that these changes in redox state are not attenuated by KATP channel antagonism.