Pathways of [Ca2+]irise evoked by angiotensin II in MDCK renal tubular cells

Investigation of effect of tectorigenin (O-methylated isoflavone) on Ca2+ signal transduction and cytotoxic responses in canine renal tubular cells

Tectorigenin, a traditional Chinese medicine, is isolated from the flower of plants such as Pueraria thomsonii Benth. It is an O-methylated isoflavone, a type of flavonoid. Previous studies have shown that tectorigenin evoked various physiological responses in different models, but the effect of tectorigenin on cytosolic-free Ca²⁺ levels ([Ca²⁺]_i) and cytotoxicity in renal tubular cells is unknown. Our research explored if tectorigenin changed Ca²⁺ signal transduction and viability in Madin-Darby Canine Kidney (MDCK) renal tubular cells. [Ca²⁺]_iin suspended cells were measured by applying the fluorescent Ca²⁺-sensitive probe fura-2. Viability was explored by using water-soluble tetrazolium-1 as a fluorescent dye. Tectorigenin at concentrations of 5-50 μM induced [Ca²⁺]_irises. Ca²⁺ removal reduced the signal by approximately 20%. Tectorigenin (50 μM) induced Mn²⁺ influx suggesting of Ca²⁺ entry. Tectorigenin-induced Ca²⁺ entry was inhibited by 10% by three inhibitors of store-operated Ca²⁺ channels, namely, nifedipine, econazole, and SKF96365. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin inhibited 83% of tectorigenin-evoked [Ca²⁺]_irises. Conversely, treatment with tectorigenin abolished thapsigargin-evoked [Ca²⁺]_irises. Inhibition of phospholipase C with U73122 inhibited 50% of tectorigenin-induced [Ca²⁺]_irises. Tectorigenin at concentrations between 10 and 60 μM killed cells in a concentration-dependent fashion. Chelation of cytosolic Ca²⁺ with 1,2-bis (2-aminophenoxy)ethane-N, N, N', N'-tetraacetic acid/acetoxy methyl did not reverse tectorigenin's cytotoxicity. Our data suggest that, in MDCK cells, tectorigenin evoked [Ca²⁺]_irises and induced cell death that was not associated with [Ca²⁺]_irises. Therefore, tectorigenin may be a Ca²⁺-independent cytotoxic agent for kidney cells.

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.

Effects of puerarin on intracellular Ca2+ and cell viability of MDCK renal tubular cells

Puerarin is a natural compound and has been used as herb medication in a number of countries, especially in Asia. The effect of puerarin on Ca²⁺ signaling is unknown in renal cells. This study examined whether puerarin affected Ca²⁺ physiology in MDCK renal tubular cells. Cytosolic free Ca²⁺ levels ([Ca²⁺]_i) were measured using the fluorescent dye fura-2. Cell viability was examined by using WST-1 assay. Puerarin induced [Ca²⁺]_i rises and the response was reduced by removing extracellular Ca²⁺. Puerarin-induced Ca²⁺ entry was not altered by protein kinase C (PKC) activity, but was inhibited by nifedipine. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) or thapsigargin partly inhibited puerarin-evoked [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) with U73122 did not change puerarin-induced [Ca²⁺]_i rises. Puerarin at 25-50μM caused cytotoxicity, 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). Collectively, in MDCK cells, puerarin induced [Ca²⁺]_i rises by evoking PLC-independent Ca²⁺ release from the endoplasmic reticulum and other unknown stores, and Ca²⁺ entry via nifedipine-sensitive, PKC-insensitive Ca²⁺ entry pathways. Puerarin also caused Ca²⁺-independent cell death.