Blockade of Calcium Influx through L-Type Calcium Channels Attenuates Mitochondrial Injury and Apoptosis in Hypoxic Renal Tubular Cells

Abstract

Abstract. In hypoxia, ATP depletion causes cellular Ca 2ϩ increase, mitochondrial injury, and apoptosis in renal tubular cells. However, the molecular basis of these observations is incompletely delineated. IRPTC, a rat renal proximal tubular cell line, was treated with antimycin A, and disturbances in cytoplasmic calcium ([Ca 2ϩ ]c) and mitochondrial calcium ion concentration ([Ca 2ϩ ]m), dissipation of mitochondrial membrane potential (⌬⌿ m ), cytochrome c release, and resultant apoptosis were examined. accumulation, mitochondrial permeability transition, cytochrome c release, caspase-9 activation, and resultant apoptosis (15.8 Ϯ 0.8% versus 8.9 Ϯ 0.7%; P Ͻ 0.01). Similar effects of azelnidipine were substantiated in an in vivo ischemia/reperfusion injury model. There were fewer terminal-deoxynucleotidyl transferase mediated dUTP nick-end labeling-positive cells in the azelnidipine-treated group (0.322 Ϯ 0.038/tubule) as compared with the vehicle-treated group (0.450 Ϯ 0.041; P Ͻ 0.05), although the antiapoptotic effect was smaller in vivo than in vitro, partly as a result of distinct levels of Bax expression. It is proposed that voltage-dependent Ca 2ϩ channels are involved in cellular and mitochondrial accumulation of Ca 2ϩ subsequent to ATP depletion and play an important role in regulating mitochondrial permeability transition, cytochrome c release, caspase activation, and apoptosis.Hypoxia is a complex stress marked by interrelated cellular changes such as ATP depletion, generation of reactive oxygen species (ROS), and elevation of intracellular Ca 2ϩ . In ischemia-reperfusion (I/R) injury, an initial decrease in cellular ATP causes an increase in extracellular potassium and intracellular sodium (1). The resultant depolarization of plasma membranes leads to Ca 2ϩ influx through voltage-dependent Ca 2ϩ channels. A steep rise in intracellular Ca 2ϩ ([Ca 2ϩ ]c) is buffered to some degree by mitochondrial Ca 2ϩ uptake. However, once a continuous increase in [Ca 2ϩ ]c exceeds the buffering capacity, these organelles become dysfunctional via opening of a nonspecific pore in the mitochondrial membrane, the permeability transition (PT) pore. Mitochondrial Ca 2ϩ overload seems to be a consequence of the rise in the cytosolic Ca 2ϩ concentration promoted by Ca 2ϩ entry through plasma membrane receptor-operated and voltage-dependent Ca 2ϩ channels. The mitochondrial dysfunction contributes to apoptotic cell death, and increasing evidence suggests the relative importance of apoptotic cell death in the pathogenesis of ischemic acute renal failure (2-4). However, the molecular mechanism by which this occurs has remained elusive. It has been shown that agents that suppress calcium influx or buffer [Ca 2ϩ ]c can prevent apoptosis in several conditions (5-10), making this possibility an attractive explanation for the observations of apoptotic cell death in I/R injury.The mitochondrial PT is a crucial checkpoint in determining cell fate. The PT pore is putatively composed of the adenine nucleotide translocator...

Effect of Tetrodotoxin from Crude Puffer Fish (Tetraodon fluviatilis) Liver Extract on Intracellular Calcium Level and Apoptosis of HeLa Cell Culture

“…These factors will activate PTP and pro-apoptotic protein to cytoplasma, altogether with apoptotic protease activating factor 1, cleaves procaspase-9 to become caspase-9, and so the apoptosis cascade begins [23]. This theory is supported by study showing that TTX is able to trigger ROS formation [24]. Both ROS and calcium are mayor inducer of PTP mitochondrial formation [25].…”

Activation of the Renin-Angiotensin System and Chronic Hypoxia of the Kidney

“…Subsequent hypoxia induces the transdifferentiation of tubular cells into myofibroblasts (epithelial mesenchymal transdifferentiation), predisposing the kidney to fibrosis (41). Hypoxia also induces the apoptosis of resident kidney cells (42)(43)(44). The overall effect is to induce a vicious cycle of fibrosis and regional hypoxia.…”

Combination Therapy with Renin-Angiotensin System Inhibitors and the Calcium Channel Blocker Azelnidipine Decreases Plasma Inflammatory Markers and Urinary Oxidative Stress Markers in Patients with Diabetic Nephropathy

“…These data suggest that AZ may ameliorate renal injuries in part by reducing oxidative stress within the tubulointerstitium. Recent studies have indicated that derangement of peritubular capillary circulation with consequent tubulointerstitial hypoxia plays a pivotal role in the pathogenesis of renal injury (37). It has been reported that AZ attenuates Ang II-induced peritubular ischemia, mitochondrial injury and apoptosis in hypoxic renal tubular cells (37,38).…”