Effect of tetramethylpyrazine (TMP) on Ca²⁺ signal transduction and cell viability in a model of renal tubular cells

Tetramethylpyrazine (TMP) is a compound purified from herb. Its effect on Ca²⁺ concentrations ([Ca²⁺]_i) in renal cells is unclear. This study examined whether TMP altered Ca²⁺ signaling in Madin-Darby canine kidney (MDCK) cells. TMP at 100–800 μM induced [Ca²⁺]_i rises, which were reduced by Ca²⁺ removal. TMP induced Mn²⁺ influx implicating Ca²⁺ entry. TMP-induced Ca²⁺ entry was inhibited by 30% by modulators of protein kinase C (PKC) and store-operated Ca²⁺ channels. Treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) inhibited 93% of TMP-evoked [Ca²⁺]_i rises. Treatment with TMP abolished BHQ-evoked [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) abolished TMP-induced responses. TMP at 200–1000 μM decreased 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. Together, in MDCK cells, TMP induced [Ca²⁺]_i rises by evoking PLC-dependent Ca²⁺ release from endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. TMP also caused Ca²⁺-independent cell death.