Effect of capsaicin on Ca²⁺ fluxes in Madin-Darby canine renal tubular cells

(Table Presented) The effect of capsaicin, a transient receptor potential vanniloid-1 (TRPV1) receptor agonist, on cytosolic free Ca²⁺ concentrations ([Ca²⁺]_i) in Madin Darby canine kidney (MDCK) cells is unclear. This study explored whether capsaicin changed basal [Ca²⁺]_i levels in suspended MDCK cells by using fura-2 as a Ca²⁺-sensitive fluorescent dye. Capsaicin at concentrations between 10-100 μM increased [Ca²⁺]_i in a concentration- dependent manner. The Ca²⁺ signal was reduced by 80% by removing extracellular Ca²⁺. Capsacin induced Mn²⁺ influx, leading to quench of fura-2 fluorescence suggesting Ca²⁺ influx. This Ca ²⁺ influx was inhibited by phospholipase A2 inhibitor aristolochic acid and the non-selective Ca²⁺ entry blocker La³⁺, but not by store-operated Ca²⁺ channel blockers nifedipine, econazole, and SK&F96365, and protein kinase C/A modulators. In Ca²⁺-free medium, pretreatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin abolished capsaicin-induced Ca²⁺ release. Conversely, pretreatment with capsaicin partly reduced thapsigargin-induced [Ca²⁺]_i rise. Inhibition of phospholipase C with U73122 did not alter capsaicin-induced [Ca²⁺]_i rise. The TRPV1 receptor antagonist capsazepine also induced significant Ca²⁺ entry and Ca²⁺ release. Collectively, in MDCK cells, capsaicin induced [Ca²⁺]_i rises by causing phospholipase C-independent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx via phospholipase A2-regulated, La³⁺-sensitive Ca²⁺ channels in a manner dissociated from stimulation of TRPV1 receptors.