Effects of NHE-1 inhibition on cardioprotection and impact on protection by K/Mg cardioplegia.

BACKGROUND: Cardiac sodium hydrogen exchanger isoform-1 (NHE-1) activity during ischemia/reperfusion contributes to myocardial injury. The effects of NHE-1 inhibition during ischemia or reperfusion and on the protection afforded by K/Mg cardioplegia was unknown. METHODS: Rabbit hearts were used for Langendorff perfusion. Control hearts were perfused for 180 minutes. Global ischemia (GI) hearts received 30 minutes normothermic global ischemia and 120 minutes reperfusion. K/Mg hearts received cardioplegia 5 minutes before ischemia. Separate groups of GI and K/Mg hearts received the NHE-1 inhibitor, HOE-642, before ischemia (HOE-642-I), at the immediate start of reperfusion (HOE-642-R), or both before ischemia and at the immediate start of reperfusion (HOE-642-IR). RESULTS: Left ventricular peak developed pressure was significantly increased in HOE-I, HOE-R, and HOE-IR throughout reperfusion (p < 0.05 versus GI). Infarct size was significantly decreased (p < 0.05 versus GI) in all groups, but was significantly increased in HOE-R as compared with HOE-IR (p < 0.05). NHE-1 inhibition with K/Mg cardioplegia significantly decreased left ventricular peak developed pressure after 90 minutes of reperfusion (p < 0.05 versus K/Mg), with no significant effect on infarct size. CONCLUSIONS: NHE-1 inhibition used alone provides cardioprotection with optimal effects being observed with HOE-IR. NHE-1 inhibition with K/Mg cardioplegia decreases postischemic functional recovery during late reperfusion.

Adenosine-enhanced ischemic preconditioning modulates necrosis and apoptosis: effects of stunning and ischemia-reperfusion.

BACKGROUND: Adenosine-enhanced ischemic preconditioning extends the protection of ischemic preconditioning by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. METHODS: The effects of adenosine-enhanced ischemic preconditioning on necrosis and apoptosis were investigated in the sheep heart using models of stunning (15 minutes regional ischemia, 120 minutes reperfusion) and ischemia-reperfusion (30 and 60 minutes regional ischemia, 120 minutes reperfusion). Ischemic preconditioned hearts received 5 minutes regional ischemia, 5 minutes reperfusion before ischemia. Adenosine-enhanced ischemic preconditioned hearts received a 10 mmol/L adenosine bolus (10 mL) through the left atrium coincident with ischemic preconditioning. Adenosine hearts received a 10 mmol/L bolus (10 mL) of adenosine. Regional ischemic hearts received no pretreatment. RESULTS: Minimal apoptosis (< 45 per 3,000 myocytes) was observed in the stunning models but was significantly increased with ischemia-reperfusion in regional ischemic hearts after 30 minutes (p < 0.05 versus ischemic preconditioning, adenosine, or adenosine-enhanced ischemic preconditioning) and in adenosine and ischemic preconditioned hearts after 60 minutes ischemia (p < 0.05 versus adenosine-enhanced ischemic preconditioning). DNA laddering was apparent after 60 minutes ischemia in regional ischemia, adenosine, and ischemic preconditioning but not in adenosine-enhanced ischemic preconditioned hearts. CONCLUSIONS: Adenosine-enhanced ischemic preconditioning significantly ameliorates necrosis and apoptosis in the regional ischemic blood-perfused heart.

Opening of mitochondrial ATP-sensitive potassium channels enhances cardioplegic protection.

BACKGROUND: Mitochondrial and sarcolemmal ATP-sensitive potassium channels have been implicated in cardioprotection; however, the role of these channels in magnesium-supplemented potassium (K/Mg) cardioplegia during ischemia or reperfusion is unknown. METHODS: Rabbit hearts (n = 76) were used for Langendorff perfusion. Sham hearts were perfused for 180 minutes. Global ischemia hearts received 30 minutes of global ischemia and 120 minutes of reperfusion. K/Mg hearts received cardioplegia before ischemia. The role of ATP-sensitive potassium channels in K/Mg cardioprotection during ischemia and reperfusion was investigated, separately using the selective mitochondrial ATP sensitive potassium and channel blocker, 5-hydroxydecanoate, and the selective sarcolemmal ATP-sensitive potassium channel blocker HMR1883. Separate studies were performed using the selective mitochondrial ATP-sensitive potassium channel opener, diazoxide, and the nonselective ATP-sensitive potassium channel opener pinacidil. RESULTS: Infarct size was 1.9%+/-0.4% in sham, 3.7%+/-0.5% in K/Mg, and 27.8%+/-2.4% in global ischemia hearts (p < 0.05 versus K/Mg). Left ventricular peak-developed pressure (percent of equilibrium) at the end of 120 minutes of reperfusion was 91%+/-6% in sham, 92% +/-2% in K/Mg, and 47%+/-6% in global ischemia (p < 0.05 versus K/Mg). Blockade of sarcolemmal ATP-sensitive potassium channels in K/Mg hearts had no effect on infarct size or left ventricular peak-developed pressure. However, blockade of mitochondrial ATP-sensitive potassium channels before ischemia significantly increased infarct size to 23%+/-2% in K/Mg hearts (p < 0.05 versus K/Mg; no statistical significance [NS] as compared to global ischemia) and significantly decreased left ventricular peak-developed pressure to 69%+/-4% (p < 0.05 versus K/Mg). Diazoxide when added to K/Mg cardioplegia significantly decreased infarct size to 1.5%+/-0.4% (p < 0.05 versus K/Mg). CONCLUSIONS: The cardioprotection afforded by K/Mg cardioplegia is modulated by mitochondrial ATP-sensitive potassium channels. Diazoxide when added to K/Mg cardioplegia significantly reduces infarct size, suggesting that the opening of mitochondrial ATP-sensitive potassium channels with K/Mg cardioplegic protection would allow for enhanced myocardial protection in cardiac operations.

Adenosine-enhanced ischemic preconditioning: adenosine receptor involvement during ischemia and reperfusion.

Adenosine-enhanced ischemic preconditioning (APC) extends the cardioprotection of ischemic preconditioning (IPC) by both significantly decreasing myocardial infarct size and significantly enhancing postischemic functional recovery. In this study, the role of adenosine receptors during ischemia-reperfusion was determined. Rabbit hearts (n = 92) were used for Langendorff perfusion. Control hearts were perfused for 180 min, global ischemia hearts received 30-min ischemia and 120-min reperfusion, and IPC hearts received 5-min ischemia and 5-min reperfusion before ischemia. APC hearts received a bolus injection of adenosine coincident with IPC. Adenosine receptor (A(1), A(2), and A(3)) antagonists were used with APC before ischemia and/or during reperfusion. GR-69019X (A(1)/A(3)) and MRS-1191/MRS-1220 (A(3)) significantly increased infarct size in APC hearts when administered before ischemia and significantly decreased functional recovery when administered during both ischemia and reperfusion (P < 0.05 vs. APC). DPCPX (A(1)) administered either before ischemia and/or during reperfusion had no effect on APC cardioprotection. APC-enhanced infarct size reduction is modulated by adenosine receptors primarily during ischemia, whereas APC-enhanced postischemic functional recovery is modulated by adenosine receptors during both ischemia and reperfusion.

Perfusion with lipopolysaccharide negative blood eliminates lipopolysaccharide induced lung injury.

We investigated whether perfusion with control blood improves pulmonary functions compromised by lipopolysaccharide (LPS) infusion. This was an animal study in a research laboratory at a university hospital by using Sprague-Dawley rats (n = 19), each weighing 325 to 350 g. All animals were pretreated with a 24 hour infusion of either LPS (5 mg/kg) or vehicle, after which, excised lungs were reperfused for 2 hours with either LPS+ or control blood. Three groups were studied: (1) group S (n = 6); LPS pretreated lungs reperfused with LPS containing blood to mimic persistent sepsis, (2) group N (n = 6); LPS pretreated lungs reperfused with control blood to mimic the removal of the septic blood components, and (3) group C (n = 7); vehicle pretreated lungs reperfused with normal blood as a control. Blood gas exchange, shunt fraction (Qs/Qt), alveolar-arterial oxygen gradient (A-aDO2), and variables for lung mechanics were measured. Leukosequestration was quantified with a myeloperoxidase (MPO) assay. The PO2 (mm Hg) values at 90 min after reperfusion in groups S, N, and C were 67.8 +/- 7.0*, 85.2 +/- 9.2, and 90.1 +/- 7.5, respectively (*p < 0.05; vs. group N and C). In addition to PO2, A-aDO2 and Qs/Qt significantly deteriorated in group S. MPO activity in the lungs after LPS infusion was significantly higher than that after vehicle infusion (1.7 +/- 0.3 vs. 0.12 +/- 0.04 units/g tissue; p < 0.001). Subsequent reperfusion with LPS+ blood (group S) increased MPO activity to 3.1 +/- 0.6 (p < 0.05), but reperfusion with normal blood (group N) caused a significant decrease to 1.1 +/- 0.2 (p < 0.05). MPO activity in group C did not significantly change compared with those after vehicle infusion. Reperfusion with control blood normalized lung function compromised by pretreatment with LPS and significantly reduced leukosequestration. These results favor the possibility that the removal of LPS+ blood components may eliminate septic lung injury.

Anti-stunning and anti-infarct effects of adenosine-enhanced ischemic preconditioning.

BACKGROUND: Adenosine-enhanced ischemic preconditioning (APC) extends the protection afforded by ischemic preconditioning (IPC) by both significantly decreasing infarct size and significantly enhancing post-ischemic functional recovery. In this study, the anti-infarct effects and the anti-stunning effects of APC in contributing to enhanced post-ischemic functional recovery were determined and compared with IPC. METHODS AND RESULTS: Sheep (n=96) were subjected to 15, 30, 45, or 60 minutes of regional ischemia and 120 minutes of reperfusion. IPC hearts received 5 minutes of regional ischemia and 5 minutes of reperfusion before ischemia/reperfusion. APC hearts received a bolus injection of adenosine coincident with IPC. Adenosine hearts (ADO) received a bolus injection of adenosine before ischemia/reperfusion. Regional ischemia (RI) hearts received no pretreatment. Infarct size/area at risk was determined by tetrazolium staining. Regional myocardial function was determined by sonomicrometry. Segment shortening after 15 minutes of ischemia in which no infarct was incurred was 32. 1+/-10.6% in RI, 70.6+/-8.5% in IPC, and 77.4+/-6.0% in APC hearts. Segment shortening after 30 minutes of ischemia was 60.7+/-6.3% in APC hearts (P:<0.05 versus RI, ADO, IPC) but was <37% in all other groups. Infarct size/area at risk after 30 and 60 minutes of ischemia was, respectively, 25.8+/-5.7% and 49.8+/-6.0% in RI, 12. 9+/-3.0% and 29.2+/-5.0% in ADO, 11.6+/-2.4% and 24.6+/-2.7% in IPC, and 5.1+/-1.6% and 12.4+/-2.0% in APC hearts (P:<0.05 versus RI, ADO, IPC). CONCLUSIONS: APC and IPC exhibit anti-infarct and anti-stunning effects in the ovine heart, but these effects are rapidly diminished with IPC. APC significantly extends these effects, providing for significantly enhanced infarct size reduction and post-ischemic functional recovery (P:<0.05 versus IPC).

Differential role of sarcolemmal and mitochondrial K(ATP) channels in adenosine-enhanced ischemic preconditioning.

Adenosine-enhanced ischemic preconditioning (APC) extends the protection afforded by ischemic preconditioning (IPC) by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. The purpose of this study was to determine whether APC is modulated by ATP-sensitive potassium (K(ATP)) channels and to determine whether this modulation occurs before ischemia or during reperfusion. The role of K(ATP) channels before ischemia (I), during reperfusion (R), or during ischemia and reperfusion (IR) was investigated using the nonspecific K(ATP) blocker glibenclamide (Glb), the mitochondrial (mito) K(ATP) channel blocker 5-hydroxydecanoate (5-HD), and the sarcolemmal (sarc) K(ATP) channel blocker HMR-1883 (HMR). Infarct size was significantly increased (P < 0.05) in APC hearts with Glb-I, Glb-R, and 5-HD-I treatment and partially with 5-HD-R. Glb-I and Glb-R treatment significantly decreased APC functional recovery (P < 0.05 vs. APC), whereas 5-HD-I and 5-HD-R had no effect on APC functional recovery. HMR-IR significantly decreased postischemic functional recovery (P < 0.05 vs. APC) but had no effect on infarct size. These data indicate that APC infarct size reduction is modulated by mitoK(ATP) channels primarily during ischemia and suggest that functional recovery is modulated by sarcK(ATP) channels during ischemia and reperfusion.

Inhibition of RNA transcription modulates magnesium-supplemented potassium cardioplegia protection.

BACKGROUND: Previously we reported that decreased postischemic functional recovery was associated with increased DNA fragmentation in the aged myocardium. Magnesium-supplemented potassium (K/Mg) cardioplegia ameliorated DNA fragmentation and enhanced post-ischemic functional recovery. We hypothesized that K/Mg cardioprotection might involve either an RNA- or a protein-dependent mechanism. METHODS: Aged rabbit hearts underwent Langendorff perfusion. Global ischemia hearts (GI) received 30 minutes of global ischemia and 60 minutes of reperfusion; K/Mg hearts received cardioplegia before global ischemia. To investigate the role of RNA and protein synthesis, K/Mg hearts were treated with alpha-amanitin or cycloheximide to inhibit RNA or protein synthesis. We also determined the quantity of DNA fragmentation and RNA/DNA ratio. RESULTS: Inhibition of RNA but not protein synthesis significantly decreased K/Mg cardioprotection and was associated with significantly decreased postischemic functional recovery (p < 0.05 versus K/Mg), increased DNA fragmentation, and decreased RNA/DNA ratio (p < 0.05 versus K/Mg). CONCLUSIONS: These results indicate that K/Mg cardioprotection in the aged myocardium was modulated by an RNA-dependent mechanism.

Alternatives for myocardial protection: adenosine-enhanced ischemic preconditioning.

Intrinsic to the development of new myoprotective protocols for use in cardiac surgery are the requirements of new protocols to be equal to or better than conventional cardioplegia in providing for enhanced post-ischemic functional recovery and decreased myocardial infarct size. Our data suggest that adenosine-enhanced ischemic preconditioning, in which a bolus injection of adenosine to the myocardium is used coincident with ischemic preconditioning, meets these requirements, providing equal cardioprotection as that of cold blood cardioplegia, significantly decreasing myocardial infarct size and significantly enhancing post-ischemic myocardial functional recovery in both the isolated perfused rabbit heart and in the in situ blood-perfused sheep heart. These results further suggest that adenosine-enhanced ischemic preconditioning may provide an effective, alternative myocardial protective protocol to reduce the morbidity and mortality in cardiac surgery.

Calcium channel blocker enhances lung preservation.

BACKGROUND: The standard program for lung transplantation employs PGE1 pretreatment for donor lungs, but its efficacy remains controversial. Calcium channel blocker has been reported more effective for reducing potassium-induced vasoconstriction. We investigate the efficacy of calcium channel blocker in the initial lung flush using rat lung transplant model. METHODS: The excised rat lungs (n = 30) were flushed with either University of Wisconsin solution (UWS) with a prior injection of 50 microg/kg PGE1 into the pulmonary artery (UWS + PGE1; n = 7), UWS only (UWS; n = 7), or UWS containing 10(-6) M nifedipine (UWS + Nif; n = 8). After storage (4 degrees C) for 24 hours, all lungs were reperfused for 2 hours using an isolated, pulsatile blood perfused lung model. Control lungs (n = 8) were reperfused immediately after harvest. Blood gas analysis and shunt fraction, lung airway resistance, dynamic lung compliance, and pulmonary vascular resistance were assessed. RESULTS: The pO2 at 30 minutes after reperfusion in the control, UWS, UWS + PGE1, and UWS + Nif group were 88.0 +/- 3.2, 49.6 +/- 2.2, 52.0 +/- 2.4, 85.1 +/- 2.1 (mmHg), respectively. Until 30 minutes after reperfusion, the pO2 in UWS and UWS + PGE1 group were significantly lower than those in UWS + Nif group (p < .001). Shunt fraction, lung airway resistance, and dynamic lung compliance also demonstrated the superiority of UWS + Nif group. CONCLUSIONS: The early graft function after storage was significantly enhanced in lungs flushed with UWS containing nifedipine. Calcium channel blocker is more effective than PGE1 in reducing the potassium-induced vasoconstriction. Optimal composition of the flush may require both calcium channel blocker for pulmonary vasodilation and PGE1 for pulmonary protection by non-vasodilatory mechanisms.

Does PGE1 attenuate potassium-induced vasoconstriction in initial pulmonary artery flush on lung preservation?

The standard clinical protocol for lung transplantation employs cold single pulmonary artery flush with Euro-Collins solution or the University of Wisconsin solution. Prostaglandin E1 (PGE1) is usually given by direct injection into the pulmonary artery to reduce pulmonary vasoconstriction caused by these intracellular, high-potassium solutions, however, the efficacy of PGE1 on lung preservation remains controversial. In this study we demonstrated that vasodilator effects of PGE1 were markedly reduced under a high-potassium condition, and that potassium-induced pulmonary vasoconstriction were inhibited by calcium channel blocker nifedipine. There are three therapeutic options in the cold single pulmonary artery flush for optimal lung transplantation, including the use of a higher dose of PGE1, use of the calcium channel blocker instead of PGE1, or the use of the extracellular, low-potassium solution such as low-potassium dextran solution for initial pulmonary artery flush before the lung harvest.

Adenosine-enhanced ischemic preconditioning provides myocardial protection equal to that of cold blood cardioplegia.

BACKGROUND: We recently described a novel myoprotective protocol-adenosine-enhanced ischemic preconditioning (APC)-that extends the protection of ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the isolated perfused heart. In the present report the efficacy of APC in the blood-perfused heart was investigated and compared with that of cold blood cardioplegia (CBC). METHODS: Cardiopulmonary bypass was instituted in 21 sheep hearts. The APC hearts (n = 6) received a bolus injection of adenosine through the aortic root at the immediate start of IPC (5 minutes of zero-flow global ischemia, followed by 5 minutes of reperfusion) before 30 minutes of global ischemia and 120 minutes of reperfusion. Nine other hearts received CBC. A control group (n = 6) received IPC only. RESULTS: Infarct size was significantly decreased (p<0.01) in the APC (3.0%+/-0.8%) and CBC (2.6%+/-0.2%) hearts compared with the IPC hearts (16.3%+/-1.6%). The preload recruitable stroke work relation, mean arterial pressure, and the time constant of pressure decay (tau) were significantly preserved (p<0.05) in APC and CBC hearts compared with IPC hearts. No significant differences were observed between APC and CBC hearts. CONCLUSIONS: Use of APC is as effective as CBC in significantly decreasing infarct size and enhancing post-ischemic functional recovery.

Adenosine-enhanced ischemic preconditioning decreases infarct in the regional ischemic sheep heart.

BACKGROUND: Recently we have reported a myoprotective protocol, adenosine-enhanced ischemic preconditioning, that extends the protection afforded by ischemic preconditioning in the isolated crystalloid-perfused heart. In this report the efficacy of adenosine-enhanced ischemic preconditioning in the in situ blood-perfused heart was investigated. METHODS: Sheep were subjected to 60 minutes of regional ischemia and 120 minutes of reperfusion. Ischemic preconditioned hearts received 5 minutes of zero flow regional ischemia and 5 minutes of reperfusion before regional ischemia. Adenosine-enhanced ischemic preconditioned hearts received a bolus injection of 10 mmol adenosine at the immediate start of ischemic preconditioning. Adenosine-treated hearts received an adenosine bolus, 10 minutes before regional ischemia. The ratio of infarct size to area at risk and mechanical function were determined. RESULTS: The infarct size to area at risk ratio in regional ischemia was 55.4%+/-2.1%. This ratio was significantly decreased with ischemic preconditioning and adenosine (22.2%+/-2.2% and 19.3%+/-1.4%, respectively; p < 0.001 versus regional ischemia) and adenosine-enhanced ischemic preconditioning (8.0%+/-2.0%, p < 0.001 versus regional ischemia and ischemic preconditioning, and p < 0.01 versus adenosine). CONCLUSIONS: Adenosine-enhanced ischemic preconditioning significantly decreases infarct size in the in situ blood-perfused heart and provides superior protection compared with ischemic preconditioning.

Adenosine-enhanced ischemic preconditioning provides enhanced postischemic recovery and limitation of infarct size in the rabbit heart.

OBJECTIVE: The purpose of this study was to determine the effect of an intracoronary bolus injection of adenosine used in concert with ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart and to compare adenosine-enhanced ischemic preconditioning with ischemic preconditioning and magnesium-supplemented potassium cardioplegia. METHODS: New Zealand White rabbits (n = 36) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 minutes; global ischemic hearts received 30 minutes of global ischemia and 120 minutes of reperfusion; magnesium-supplemented potassium cardioplegic hearts received cardioplegia 5 minutes before global ischemia; ischemic preconditioned hearts received 5 minutes of zero-flow global ischemia and 5 minutes of reperfusion before global ischemia; adenosine-enhanced ischemic preconditioned hearts received a bolus injection of adenosine just before the preconditioning. To separate the effects of adenosine from adenosine-enhanced ischemic preconditioning, a control group received a bolus injection of adenosine 10 minutes before global ischemia. RESULTS: Infarct volume in global ischemic hearts was 32.9% +/- 5.1% and 1.03% +/- 0.3% in control hearts. The infarct volume decreased (10.23% +/- 2.6% and 7.0% +/- 1.6%, respectively; p < 0.001 versus global ischemia) in the ischemic preconditioned group and control group, but this did not enhance postischemic functional recovery. Magnesium-supplemented potassium cardioplegia and adenosine-enhanced ischemic preconditioning significantly decreased infarct volume (2.9% +/- 0.8% and 2.8% +/- 0.55%, respectively; p < 0.001 versus global ischemia, p = 0.02 versus ischemic preconditioning and p = 0.05 versus control group) and significantly enhanced postischemic functional recovery. CONCLUSIONS: Adenosine-enhanced ischemic preconditioning is superior to ischemic preconditioning and provides equal protection to that afforded by magnesium-supplemented potassium cardioplegia.

Adenosine-enhanced ischemic preconditioning provides enhanced cardioprotection in the aged heart.

BACKGROUND: Recently we have reported a novel myo-protective protocol "adenosine-enhanced ischemic preconditioning" (APC), which extends and amends the protection afforded by ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the mature rabbit heart. However, the efficacy of APC in the senescent myocardium was unknown. METHODS: The efficacy of APC was investigated in senescent rabbit hearts and compared with magnesium-supplemented potassium cardioplegia (K/Mg) and IPC. Global ischemia (GI) hearts were subjected to 30 minutes of global ischemia and 120 minutes of reperfusion. Ischemic preconditioning hearts received 5 minutes of global ischemia and 5 minutes of reperfusion before global ischemia. Magnesium-supplemented potassium cardioplegia hearts received cardioplegia just before global ischemia. Adenosine-enhanced ischemic preconditioning hearts received a bolus injection of adenosine in concert with IPC. To separate the effects of adenosine from that of APC, a control group (ADO) received a bolus injection of adenosine 10 minutes before global ischemia. RESULTS: Infarct size was significantly decreased to 18.9%+/-2.7% with IPC (p<0.05 versus GI); 17.0%+/-1.0% with ADO (p<0.05 versus GI); 7.7%+/-1.3% with K/Mg (p<0.05 versus GI, IPC, and ADO); and 2.1%+/-0.6% with APC (p<0.05 versus GI, IPC, ADO, and K/Mg; not significant versus control). Only APC and K/Mg significantly enhanced postischemic functional recovery (not significant versus control). CONCLUSIONS: Adenosine-enhanced ischemic preconditioning provides similar protection to K/Mg cardioplegia, significantly enhancing postischemic functional recovery and decreasing infarct size in the senescent myocardium.

Developmental differences in cytosolic calcium accumulation associated with global ischemia: evidence for differential intracellular calcium channel receptor activity.

BACKGROUND: Cytosolic calcium ([Ca2+]i) accumulation during global ischemia is increased 30% more in the aged compared with the mature heart and is associated with decreased functional recovery. Recently, we have shown that [Ca2+]i accumulation occurs via the ryanodinc sensitive (RyR) and the inositol (1,4,5) triphosphate calcium channels (IP3) but not the Na+/Ca2+ exchanger in both the mature and aged heart, suggesting that the increase in [Ca2+]i accumulation in the aged heart may result from either alteration of intracellular Ca2+ channel receptor activity or abundance. METHODS: [3H]-Ryanodine and [3H]-Inositol (1,4,5) triphosphate binding was determined in mature (MAT; 15 to 20 weeks) and aged (AGE; >130 weeks) rabbit hearts perfused for 60 minutes (control) or perfused for 30 minutes then subjected to 30 minutes of global ischemia (global ischemia). RESULTS: RyR and IP3R activities in control were decreased significantly (P<.05) in aged compared with mature hearts. Global ischemia significantly decreased RyR activity in MAT but not in AGE. IP3R was significantly increased (P<.05) during global ischemia in AGE but not in MAT. Northern and Western blot analysis indicated that there were no differences in RyR or IP3R mRNA or protein levels between MAT and AGE. CONCLUSIONS: Aging alters intracellular Ca2+ channel activity. Ca2+ channel activity is decreased during global ischemia in mature but increased in the aged heart resulting in increased [Ca2+]i accumulation. Differences in RyR and IP3R activities were shown not to be the result of a decrease in receptor mRNA or protein levels in the aged compared with the mature heart.

Amelioration of ischemic calcium overload correlates with high-energy phosphates in senescent myocardium.

Previously, we have shown that potassium and magnesium (K-Mg, 20 mM each) cardioplegia ameliorated cytosolic calcium ([Ca2+]i) accumulation and was associated with enhanced functional recovery after surgically induced global ischemia in the aged heart. K-Mg cardioplegia was also shown to enhance cytosolic cytochrome oxidase I activity and mRNA levels, suggesting that enhanced functional recovery may involve the preservation of high-energy phosphates. To investigate this hypothesis, 31P nuclear magnetic resonance was used to measure serial alterations in phosphocreatine (PCr), inorganic phosphate, nucleoside triphosphate (NTP), intracellular free magnesium (Mgf), and intracellular pH (pHi) in Langendorff-perfused, aged (135 wk) rabbit hearts during preischemia, global ischemia (30 min), and reperfusion (30 min). K-Mg cardioplegia retarded PCr depletion (P < 0.05) and significantly enhanced NTP preservation (P < 0.05) during ischemia and reperfusion. K-Mg cardioplegia also attenuated the increase in Mgf during ischemia (P < 0.05). These results were correlated with amelioration of [Ca2+]i accumulation during ischemia and preservation of left ventricular function after reperfusion and suggest that optimal functional recovery from surgically induced ischemia is provided by K-Mg cardioplegia in the aged myocardium.

Mechanisms of in vitro cardioprotective action of magnesium on the aging myocardium.

Studies examining the effects of aging on the myocardium have indicated that with advancing age there are anatomical, mechanical, ultrastructural, and biochemical alterations which compromise the adaptive response of the heart and make the senescent myocardium less tolerant to surgically-induced ischemia. With the increased incidence of elderly patients as candidates for complex cardiac surgery, the investigation into methods which will increase survivability and enhance myocardial protection are of paramount importance. Previous reports have indicated that surgically-induced global ischemia is associated with alteration in cytosolic calcium accumulation ([Ca2+]i), and that the level of post-ischemic functional recovery can be correlated with control of [Ca2+]i Cardioplegia (high potassium arrest) partially ameliorates the adverse effects associated with global ischemia however; the use of magnesium (magnesium supplemented potassium icardioplegia) has been shown to provide superior myocardial protection during global ischemia and to allow for enhanced post-ischemic functional recovery. The cardioprotective mechanisms of magnesium supplemented potassium cardioplegia which allow for decreased morbidity and mortality in the cardiac surgical patient has been shown to act at the level of the sarcolemma, mitochondria and the nucleus. and may be associated with myocardial gene expression in the aged heart. In this report these mechanisms are reviewed.

Developmental differences in cytosolic calcium accumulation associated with surgically induced global ischemia: optimization of cardioplegic protection and mechanism of action.

OBJECTIVE: The effect of cardioplegic solutions with high concentrations of potassium or magnesium (or both) on cytosolic calcium accumulation was investigated with fura-2 in isolated perfused mature (n = 24) and aged (n = 24) rabbit hearts. METHODS: We compared cytosolic calcium accumulation before ischemia (control), during 30 minutes of ischemia and 30 minutes of reperfusion under global ischemia, or after treatment with potassium (20 mmol/L), magnesium (20 mmol/L), or both. RESULTS: Cytosolic calcium accumulation was increased during global ischemia in the mature heart (from 178.7 +/- 24.2 in the control group to 393.6 +/- 25.5 nmol/L; p < 0.005) and in the aged heart (from 187.4 +/- 18.7 in the control group to 501.0 +/- 46.1 nmol/L; p < 0.005). Potassium reduced cytosolic calcium accumulation during ischemia in both the mature and aged hearts (300.9 +/- 23.2 and 365.2 +/- 27.7 nmol/L, respectively; p < 0.05 vs global ischemia). Magnesium and potassium/magnesium completely controlled cytosolic calcium accumulation in the mature heart (198.7 +/- 27.5 nmol/L; p < 0.01 vs global ischemia and p < 0.05 vs potassium: 182.3 +/- 22.7 nmol/L; p < 0.05 vs global ischemia and potassium, respectively). Magnesium and potassium/magnesium attenuated cytosolic calcium accumulation in the aged heart (261.3 +/- 26.7, 262.3 +/- 25.2 nmol/L, respectively; p < 0.01 vs global ischemia). These changes in cytosolic calcium accumulation correlated with improved post-ischemic ventricular function. To investigate the mechanism(s) of magnesium-supplemented cardioplegic inhibition of cytosolic calcium accumulation, we performed parallel studies (n = 43) using nifedipine, ryanodine, and dimethylthiourea. Nifedipine with or without ryanodine reduced cytosolic calcium accumulation. Dimethylthiourea did not alter cytosolic calcium accumulation during global ischemia. Our results suggest that cytosolic calcium accumulation during global ischemia was mainly increased via the sarcolemmal 1-type calcium channel and the sarcoplasmic reticulum calcium-release channel. The modulating action of potassium/magnesium cardioplegia on cytosolic calcium accumulation during ischemia would appear to act through the inhibition of the myocardial 1-type calcium channel and the sarcoplasmic reticulum calcium-release channel. CONCLUSION: Senescent cardiac dysfunction correlates with increased ischemia-induced cytosolic calcium accumulation. Magnesium-supplemented potassium cardioplegia ameliorates this age-related phenomenon at normothermia and may have important implications in myocardial protection in the elderly population.