Al4 Abstracts. Xth Meeting of ISHR Latin American Section

26 PACING DURlNG lSCHEMlA ALTERS PHOSPHOlAMBAN PHOSPHORYLATK)N PAllERN BUT DOES NOT ALTER THE DEPRESSED CARDlAC RESPONSE TO MDRfZNERGIC

7 STMUlATlON OF ISCHEMlA-REPERFUSED HEARTS Paola Ferrero, Cecilia Mundifla-Weilenmann, Matilde Said, Leticia Vittone, Alicia Mattiazzi. Centro de lnvestigaciones Cardiovasculares, Facultad de Medicina, La Plata, Argentina.

27 PARTICIPATION OF THE SARCOPLASMIC RETICULUM IN THE MYOCARDIAL PRECONDITIONING BY TACHYCARDlA IN DOGS. Gina Sanchez, Paulina Donoso, Pilar Macho, Raul Domenech. lnstituto de Ciencias Biomedicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.

Sarcoplasmic reticulum (SR) Ca2+ uptake is altered in the reversible contractile dysfunction that occurs after a brief period of ischemia. We previously showed in Langendorff- perfused rat hearts that the pfiosphorylation of phospholamban (PLB), a cardiac SR Ca uptake-regulating protein, was modified in ischemia and reperfusion: Ser (PKA site) was phosphorylated at the end of ischemia and Th$’ (CaMKII site) at the beginning of ischemia and reperfusion. In the protocol used, pacing (P) was interrupted during the 20 min-ischemia. We now examined the effect of keeping P during ischemia. P accelerated the increase in left ventricular end-diastolic pressure during ischemia and decreased the recovery of left ventricular developed pressure (LVDP). At the end of 30 min-reperfusion, LVDP was 52.3*11.7% in non-paced hearts, n=7 vs 15.7*4.9% in paced hearts, n=4. Compared to non-paced hearts, in paced hearts the ischemia-induced increase in SeP phosphorylation was anticipated and that of Thr” phosphorylation was enhanced and prolonged, whereas the reperfusion-induced Thr” phosphorylation was not affected. Both in non-paced and paced hearts the inotropic, relaxant and PLB phosphotylation response to a 6-adrenergic stimulation was similarly diminished. The results indicate that P during ischemia affects PLB phosphorylation pattern but does not modify the depressed cardiac response to a 6- adrenergic challenge of ischemia-reperfused hearts.

REPERFUSIDN FAILURE: ROLE DF BOTH MDDES DF N&I. EXCHANGER AND SARCDPLAslyC RETICULUM. Alicia EConscltni; Gracieta Yuln; Pabic Quimga; Maria G.Voloti. Dpto.Cs.BNt6gii, FacCllncias G&as. UNLP, La plats. Argentina.

Cardiilegia (CPG, 25mMK-05mMCa) protected against cardiac ischemia reperfuslon failure (CIRF) in rat Since CPG increased Ca- dependent resfing heat (1) ws studied if pmtection was due to effects on N&a-exchanger (Nalca-ex) sarcoplasmic reticulum (SR) or &ochondrial recovery (MR). Isolated rat ventricles were perfused with Krebs8rnMK-2mM-Cs (C) at 3o’C. Intravenbicular pressure (P) was measured in he&s exposed to C or 28 min CPG before 45min I and 45min R. Heark wet’s freezed tc measuring ATP and PCr by HPLC. CPG incressed P recovery by R (P%R) to 72i5% (vs. 50+7% in c’) and avoided diastotll pressure increase (P&8*8 vs. +1&4 mmHg ‘). Cytosolic PCr/ATF ra8o increased from 2.Q0.2 in C b 8.7il.7 by I (3 and 5.7i0.8 by R (‘) while CPG kept PCrlATP at 28tl.l by I and 3.Q0.8 by R (NS). PCr/P ratio (0.2&0.88) was not &red by R in C MK CPGhearts. Caffeine 8rnN during CPG or C previous tc I decreased NR slmilarty in both (by 25%) and did not &er Pd nor PO/F ratlo by R. Decreasing N&a gradient during CPG decreased P%R (47*8%') and PCrlp (to 0.1&0.05”) and increased Pd (+I&6

mmHg’) but did not affect them during C (57i5%, 0.22iO.03, -5+I, resp.). Adding of KBR7943 5 pM (NdCa-ex reversemode inhibitor) decreased P%R (to lQ2%3 during CPG but not during C (5&3%). Results suggest that CPG pmtectton agsinst CIRF could be related to improvement in MR (ATP content) and tc psrticipation of NalCa-ex. by increasing Ca-efflux or by cycling Ca between forward and reverse- nmles, but is not retated to S.R. (=p<o.os). (1) AcNPhysScarrd 180,1997. Graaf X294-UNLP.

We recently showed that brief periods of tachycardia (T) prior to a prolonged coronary artery occlusion reduces infarct size. Since T releases Ca*’ from the sarcoplasmic reticulum (SR) and Ca” induces preconditioning, we studied the effect of ischemia (IS) on cytosolic Ca2+ regulation and its changes by preconditioning with T. Cardiac SR vesicles were prepared from the left ventricle of dogs with the following protocols:l)control dogs,N=7; 2) five periods,5 min each, of T, N=6; 3)myocardial IS by coronary occlusion without prior T, N=6; 4) T followed by myocardial IS, N=7. IS decreased [H’]-Ryanodine binding from 3.1kO.2 to 1.6* 0.3 pmollmg protein (PcO.01) and maximum oxalate supported Ca*+ uptake from 91+11 to 28+1 nmollmg proteinlmin (PeO.05) and increased Ca2+ release constant from 113*4 to 222+14 s”(P<O.OOl). Preconditioning+with T reverted all these effecis. T by itself increased Ca release constant and [H ]-Ryanodine binding by 44% and 68% respectively (P<O.OOl). IS decreased SERCA-2 and phospholamban contents by 35% (P<O.Ol), effects that were also prevented by preconditioning with T. We conclude that T induces changes in the SR that prevent the cytosolic Ca2’ overload produced by IS. Supported by FONDECYT Grants1000642 and 8980009.

19 THE CYCLOOXYGENASE PATHWAY IS NOT INVOLVED IN LATE PRECONDITIONING PRo-fEcmoN AGAINST ARRHYTHw~A& IN CONSCIOUS SHEEP Elena C. Lascano, Hector F. del Valle, Jorge A. Negroni. Universidad Favaloro, Buenos Aires, Argentina.

Introduction: Prostanoids, derived from the cyclooxygenase (COX) pathway of arachidonic acid metabolism have a role in late preconditioning (LP) since COX inhibition abolishes LP protection against infarction and stunning. Objective: We analysed the participation of COX pathway in LP protection against arrhythmias in conscious sheep. Methods: Sheep were divided in: control (C): 12 min ischemia (I) by occlusion of the left coronary artery and 10 min reperfusion (R) ; LP: six periods of 5 min l-5 min R 24 h before the 12 min I and 10 min R; LPA: same as LP, except that 20 me/kg aspirin-DL-lysin was administered 10 min prior to the first preconditioning ischemia to inhibit COX. Arrhythmias were classified as premature beats (EB):l , salvos (S):2, ventricular tachycardia (VT):3, ventricular fibrillation (VF):4 and death (D):5, and assessed by

I I I I I I Number of animals with the anhythmic event/total number of animals; ASI: mean*SE; T pcO.01 vs C. Conclusions: LP protection against arrhythmias in conscious sheep is not abrogated by administration of aspirin, indicating non-involvement of the COX pathway.