Mibefradil alters intracellular calcium concentration by activation of phospholipase C and IP 3 receptor function.

Mibefradil is a tetralol derivative originally developed as an antagonist of T-type voltage-gated calcium (Ca 2+ ) channels to treat hypertension when used at nanomolar dosage. More recently, its therapeutic application in hypertension has declined and has been instead repurposed as a treatment of cancer cell proliferation and solid tumor growth. Beyond its function as a Ca v blocker, the micromolar concentration of mibefradil can stimulate a rise in [Ca 2+ ] cyt although the mechanism is poorly known. The chanzyme TRPM7 (transient receptor potential melastanin 7), the release of intracellular Ca 2+ pools, and Ca 2+ influx by ORAI channels have been associated with the increase in [Ca 2+ ] cyt triggered by mibefradil. This study aims to investigate the cellular targets and pathways associated with mibefradil's effect on [Ca 2+ ] cyt . To address these questions, we monitored changes in [Ca 2+ ] cyt in the specialized mouse epithelial cells (LS8 and ALC) and the widely used HEK-293 cells by stimulating these cells with mibefradil (0.1 μM to 100 μM). We show that mibefradil elicits an increase in [Ca 2+ ] cyt at concentrations above 10 μM (IC 50 around 50 μM) and a fast Ca 2+ increase capacity at 100 μM. We found that inhibiting IP 3 receptors, depleting the ER-Ca 2+ stores, or blocking phospholipase C (PLC), significantly decreased the capacity of mibefradil to elevate [Ca 2+ ] cyt. Moreover, the transient application of 100 μM mibefradil triggered Ca 2+ influx by store-operated Ca 2+ entry (SOCE) mediated by the ORAI channels. Our findings reveal that IP 3 R and PLC are potential new targets of mibefradil offering novel insights into the effects of this drug.