Naproxen-induced Ca²⁺ movement and death in MDCK canine renal tubular cells

Naproxen is an anti-inflammatory drug that affects cellular calcium ion (Ca²⁺) homeostasis and viability in different cells. This study explored the effect of naproxen on [Ca²⁺]ⁱ and viability in Madin-Darby canine kidney cells (MDCK) canine renal tubular cells. At concentrations between 50 μM and 300 μM, naproxen induced [Ca²⁺]ⁱ rises in a concentration-dependent manner. This Ca²⁺ signal was reduced partly when extracellular Ca²⁺ was removed. The Ca²⁺ signal was inhibited by a Ca²⁺ channel blocker nifedipine but not by store-operated Ca²⁺ channel inhibitors (econazole and SKF96365), a protein kinase C (PKC) activator phorbol 12-myristate 13-acetate, and a PKC inhibitor GF109203X. In Ca²⁺-free medium, pretreatment with 2,5-di-tert-butylhydroquinone or thapsigargin, an inhibitor of endoplasmic reticulum Ca²⁺ pumps, partly inhibited naproxen-induced Ca²⁺ signal. Inhibition of phospholipase C with U73122 did not alter naproxen-evoked [Ca²⁺]ⁱ rises. At concentrations between 15 μM and 30 μM, naproxen killed cells in a concentration-dependent manner, which was not reversed by prechelating cytosolic Ca²⁺ with the acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid acetoxymethyl. Annexin V/propidium iodide staining data suggest that naproxen induced apoptosis. Together, in MDCK renal tubular cells, naproxen induced [Ca²⁺]ⁱ rises by inducing Ca²⁺ release from multiple stores that included the endoplasmic reticulum and Ca²⁺ entry via nifedipine-sensitive Ca²⁺ channels. Naproxen induced cell death that involved apoptosis.