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

The effect of angiotensin II (Ang II) on cytosolic Ca²⁺ concentrations ([Ca²⁺]i) in MDCK renal tubular cells was explored. The Ca²⁺-sensitive fluorescent dye fura-2 was applied to measure [Ca²⁺]i. Ang II at concentrations of 5-40 µM induced a [Ca²⁺]i rise in a concentration-dependent manner. The response was reduced partly by removing Ca²⁺. Ang II evoked store-operated Ca²⁺ entry that was inhibited by La²⁺ and Gd³⁺. In the absence of extracellular Ca²⁺, incubation with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) or thapsigargin abolished Ang II-induced Ca²⁺ release. Inhibition of phospholipase C with U73122 abolished Ang II-induced [Ca²⁺]i rise. Three Ang II analogues [(ASN1,VAL5)-Ang II acetate, (SAR1,THR8)-Ang II acetate, (VAL5)-Ang II acetate] failed to induce a [Ca²⁺]i rise. Together, in MDCK cells, Ang II induced a [Ca²⁺]i rise via Ca²⁺ entry through store-operated Ca²⁺ channels and phospholipase C-dependent Ca²⁺ release from the endoplasmic reticulum. Moreover, Ang II's amino acid sequence is important in its stimulatory effect on [Ca²⁺]i.