Fasting limits the increase in intracellular calcium during ischemia in isolated rat hearts

Abstract

Introduction Fasting has been shown to limit ischemic injury and improve functional activity after global ischemia. Because calcium overload is considered a mechanism of ischemic injury, we hypothesized that fasting would limit the accumulation of intracellular calcium [Ca]_i during ischemia, potentially due to reduced accumulation of intracellular sodium [Na]_i. Methods To address this hypothesis, hearts isolated from rats fed either a normal diet or fasted for 24 hours underwent 20 min of global ischemia at 37°. In addition to functional parameters, [Na]_i and [Ca]_i were measured using ²³Na and ¹⁹F spectroscopy using thulium-DOTP⁻⁵ and 5F-BAPTA, respectively. In vitro measurement of sarcoplasmic reticulum calcium uptake and release, as well as activity of the sarcolemmal Na-Ca exchanger, was performed in hearts from fed and fasted animals under baseline and ischemic conditions. Results Hearts from fasted animals showed greater recovery of developed pressure (37 ± 9 vs. 11 ± 6 cm H₂O, p < 0.05) and less contracture (end-diastolic pressure 25 ± 2 vs. 47 ± 2 cm H₂O, p < 0.05) by the end of the reperfusion period. [Na]_i was similar in the 2 groups during the first half of the ischemic period, albeit with a higher concentration of [Na]_i in hearts from fed compared to fasted animals at reperfusion. Fasting markedly limited calcium accumulation during ischemia, with end-ischemic calcium being 419 ± 46 nM in the hearts from fasted animals and 858 ± 140 nM in the hearts from fed animals (p < 0.01). There was no significant effect of fasting on calcium uptake or release by the SR, nor on sarcolemmal Na-Ca exchange activity. Conclusions Fasting for 24 hours improves functional recovery and markedly limits [Ca]_i accumulation during ischemia and early reperfusion. The mechanism for this phenomenon remains to be elucidated.