Enhanced transient receptor potential channel‐mediated Ca²⁺ influx in the cells with phospholipase C‐δ1 overexpression: its possible role in coronary artery spasm

We reported that coronary spasm was induced in the transgenic mice with the increased phospholipase C ( PLC )‐δ1 activity. We investigated the effect of enhanced PLC ‐δ1 on Ca 2+ influx and its underlying mechanisms. We used human embryonic kidney ( HEK )‐293 and coronary arteries smooth muscle cells ( CASMC ). Intracellular free Ca 2+ concentration ([Ca 2+ ] i ; n m ) was measured by fura‐2, and Ca 2+ influx was evaluated by the increase in [Ca 2+ ] i after addition of extracellular Ca 2+ . Acetylcholine ( AC h) was used to induce Ca 2+ influx. AC h‐induced peak Ca 2+ influx was 19 ± 3 in control HEK ‐293 cells and 71 ± 8 in the cells with PLC ‐δ1 overexpression ( P < 0.05 between two groups). Nifedipine partially suppressed this Ca 2+ influx, whereas either 2‐ APB or knockdown of classical transient receptor potential channel 6 ( TRPC 6) blocked this Ca 2+ influx. In the human CASMC , AC h‐induced peak Ca 2+ influx was 29 ± 6 in the control and was increased to 45 ± 16 by PLC ‐δ1 overexpression ( P < 0.05). Like HEK ‐293 cells, pretreatment with nifedipine partially suppressed Ca 2+ influx, whereas either 2‐ APB or knockdown of TRPC 6 blocked it. AC h‐induced Ca 2+ influx was enhanced by PLC ‐δ1 overexpression, and was blocked partially by nifedipine and completely by 2‐ APB . TRPC ‐mediated Ca 2+ influx may be related to the enhanced Ca 2+ influx in PLC ‐δ1 overexpression.