Pharmacological manipulation of Ins(1,4,5)P₃signaling mimics preconditioning in rabbit heart

Abstract

Recent evidence revealed biphasic alterations in myocardial concentrations of the second messenger inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] with ischemic preconditioning (PC), i.e., increase during brief PC ischemia and decrease early during sustained test occlusion. Our aim was to determine whether an agonist and an antagonist of Ins(1,4,5)P(3) signaling (D-myo-inositol-1,4,5-trisphosphate hexasodium salt [D-myo-Ins(1,4, 5)P3] and 2-aminoethoxydiphenyl borate (2-APB), respectively), given such that they mimic this biphasic profile, would mimic infarct size reduction with PC. To test this concept, isolated, buffer-perfused rabbit hearts received no intervention (control), ischemic PC, D-myo-Ins(1,4,5)P3, D-myo-Ins(1,4,5)P(3) + PC, 2-APB, or 2-APB + PC. All hearts then underwent 30-min coronary occlusion and 2 h reflow, and infarct size was delineated by tetrazolium staining. In addition, the effects of D-myo-Ins(1,4,5)P3 and 2-APB on Ins(1,4,5)P3 signaling were evaluated in isolated fura 2-loaded rat cardiomyocytes. Mean infarct size was reduced with PC and in all D-myo-Ins(1,4,5)P3- and 2-APB-treated groups versus control (59 and 42-55%, respectively, vs. 80% of myocardium at risk, P < 0.05). Thus pharmacological manipulation of Ins(1,4,5)P3 signaling mimics the cardioprotection achieved with ischemic PC in rabbit heart.

The SR/ER-mitochondria calcium crosstalk is regulated by GSK3β during reperfusion injury

“…Our proposal is in line with previous reports demonstrating that SR/ER loses almost 90% of its Ca 2+ at the onset of reperfusion, 32 and that specific IP 3 R channels inhibition can protect the heart at reperfusion. 33 One may question whether IP 3 R may be a direct or an indirect substrate of GSK3β. Such mechanism remains to be investigated indepth in future studies.…”

Reduction of infarct size with d-myo-inositol trisphosphate: role of PI3-kinase and mitochondrial KATP channels

“…Experiments were conducted by using the isolated buffer-perfused rabbit heart model of regional ischemia (2,6,10,24). In brief, New Zealand White rabbits weighing 2.5-3.5 kg were anesthetized with an intramuscular injection of ketamine plus xylazine (150 mg and 100 mg, respectively).…”

“…This was preceded by an intervention period, during which hearts were allocated into 15 treatment groups (n ϭ 6 -8 hearts/group). Five groups of hearts were randomly assigned to receive D-myo-Ins(1,4,5)P3 (CalBiochem, La Jolla, CA), dissolved in 5 ml buffer and administered over 1 min, beginning 25 min before the onset of coronary artery occlusion, via a sidearm located immediately proximal to the heart (final concentration in perfusate was 6 M) (10,24). This dose and timing of D-myoIns(1,4,5)P 3 treatment was shown in early pilot studies to trigger optimal protection in this model (data not shown).…”

“…Previous studies (10,24) have shown that prophylactic administration of exogenous D-myo-Ins(1,4,5)P 3 hexasodium, the sodium salt of Ins(1,4,5)P 3 , renders the rabbit heart resistant to a subsequent, sustained ischemic insult and initiates a reduction of infarct size similar in magnitude to that achieved with ischemic preconditioning (PC), the current "gold standard" of experimental cardioprotection. The mechanisms responsible for the infarct-sparing effect of exogenous D-myo-Ins(1,4,5)P 3 are, however, largely unknown; although recent evidence has identified Ins(1,4,5)P 3 -receptor binding and communication via gap junctions/hemichannels as elements of the trigger phase of D-myo-Ins(1,4,5)P 3 -induced protection (24), the distal signaling pathways contributing to the increased resistance to ischemia afforded by D-myo-Ins(1,4,5)P 3 have, to date, not been investigated.…”

Direct Action of Endothelin-1 on Podocytes Promotes Diabetic Glomerulosclerosis

“…67 Cells subcultured for 4 days in chambered coverglass (Lab-Tek) were loaded by incubation with 2.5 mmol/L Fura-2AM (TEFLabs) plus 0.02% pluronic acid F-127 (Molecular Probes, Inc.), in Locke buffer for 20 minutes at 37°C in a humidified air atmosphere. Cells were rinsed with buffer and mounted on a microscope stage (Axiovert, 320 objective; Zeiss) during a 15-minute waiting period for the de-esterification of Fura-2AM.…”