Effect of Protriptyline on [Ca²⁺]i and Viability in MDCK Renal Tubular Cells

Protriptyline has been used as an antidepressant. Clinically it has been prescribed in the auxiliary treatment of cancer patients. However, its effect on Ca²⁺ signaling and related physiology is unknown in renal cells. This study examined the effect of protriptyline on cytosolic free Ca²⁺ concentrations ([Ca²⁺]i) and viability in Madin-Darby canine kidney (MDCK) tubular cells. Protriptyline induced [Ca²⁺]i rises concentration-dependently. The response was reduced by 20% by removing extracellular Ca²⁺. Protriptyline-induced Ca²⁺ entry was not altered by protein kinase C (PKC) activity but was inhibited by 20% by three modulators of store-operated Ca²⁺ channels: nifedipine, econazole and SKF96365. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5- di-tert-butylhydroquinone (BHQ) or thapsigargin partially inhibited protriptyline-evoked [Ca²⁺]i rises. Conversely, treatment with protriptyline inhibited partially BHQ or thapsigargin-evoked [Ca²⁺]i rises. Inhibition of phospholipase C (PLC) with U73122 did not change protriptyline-induced [Ca²⁺]i rises. Protriptyline at 5-200 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid-acetoxymethyl ester (BAPTA/ AM). Together, in MDCK cells, protriptyline induced [Ca²⁺]i rises by evoking PLC-independent Ca²⁺ release from the endoplasmic reticulum and other unknown stores, and Ca²⁺ entry via PKCinsensitive store-operated Ca²⁺ entry. Protriptyline also caused Ca²⁺-independent cell death.