Cytosolic [Ca2+], [Na+], and pH in guinea pig ventricular myocytes exposed to anoxia and reoxygenation

Abstract

The aim of this study was to evaluate whether the magnitude and time course of the intracellular acidification observed in anoxic cardiac myocytes was sufficient to protect against reoxygenation-induced hypercontracture. Cytosolic [Ca2+], [Na+], and pH were measured using fluorescent indicators in myocytes that were first subjected to both anoxia and glucose deprivation and then oxygen and glucose restoration 15-30 min after the onset of rigor. The cytosol underwent a profound acidification early in anoxia (pH 7.21 to 6.84) that reached a plateau at the time of rigor contracture. In contrast, [Na+] rose throughout anoxia. Cytosolic [Ca2+] underwent little rise during anoxia, but reoxygenation induced a large spike in [Ca2+]. Reoxygenation also induced a significant secondary acidification of the cytosol that was apparently induced by the spike in [Ca2+]. The characteristics of this secondary acidification were deemed sufficient to provide partial protection against the hypercontracture associated with the reoxygenation-induced [Ca2+] transient.

Activation of α1B-adrenoceptors alleviates ischemia/reperfusion injury by limitation of mitochondrial Ca2+ overload in cardiomyocytes

“…The observation that development of [Ca 2+ ] c and [Ca 2+ ] m overload during simulated I/R accompanied with the impaired cell contraction is consistent with our previous findings [18,19] and other reports in I/R [13] and anoxia/reoxygenation cells [32]. Several lines of evidence suggest that activation of α 1 -ARs mimics IP in rats and other species [4,8,33] through the mechanisms related to nitric oxide (NO) [8], PKC isoforms [7,20] and mitoK ATP channels [33].…”

Na+/Ca2+ exchanger plays a key role in inducing apoptosis after hypoxia in cultured guinea pig ventricular myocytes

“…Other studies have shown that [Ca 2ϩ ] i is elevated in various models of ischemia (31,40) and that the NCX could be responsible for this rise in [Ca 2ϩ ] i (16,45). In our model, an elevated cytosolic Na ϩ concentration precedes the [Ca 2ϩ ] i overload that occurs during reoxygenation (7,34), and this overload is clearly due to Ca 2ϩ influx through reverse-mode NCX activity. The key evidence in support of this comes from adult cultured guinea pig ventricular myocytes treated for 5-6 days with an antisense oligonucleotide directed to the cardiac NCX1 start site (8).…”

“…Dual-emission images at wavelengths longer or shorter than 445 nm were acquired for indo-1. Standard ratiometric analysis procedures were applied to the indo-1 images as previously described (5,34). The [Ca 2ϩ ]i values are reported as relative changes in the indo-1 fluorescence ratio: an increase in [Ca 2ϩ ]i is seen as an increase in the fluorescence ratio.…”

ROS are required for rapid reactivation of Na+/Ca2+exchanger in hypoxic reoxygenated guinea pig ventricular myocytes

“…Female Hartley guinea pigs were anesthetized with an intraperitoneal injection of pentobarbital sodium before the hearts were excised. Cells were isolated using an established collagenase dispersion technique (26). A total of 40 animals were used to prepare myocytes for this study; each figure (except Fig.…”

“…Experiments were carried out at 22°C to ensure compatibility with earlier studies (6,7). Quiescent myocytes were made hypoxic in a glass, gas-tight petri dish (6,26). Hypoxia was maintained for 20 min postrigor at which time the hypoxic solution was removed and replaced with oxygenated solution that contained 11 mmol/l glucose.…”