Enhanced transient receptor potential channel-mediated Ca 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 influx and its underlying mechanisms. We used human embryonic kidney (HEK)-293 and coronary arteries smooth muscle cells (CASMC). Intracellular free Ca concentration ([Ca ] ; nm) was measured by fura-2, and Ca influx was evaluated by the increase in [Ca ] after addition of extracellular Ca . Acetylcholine (ACh) was used to induce Ca influx. ACh-induced peak Ca 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 influx, whereas either 2-APB or knockdown of classical transient receptor potential channel 6 (TRPC6) blocked this Ca influx. In the human CASMC, ACh-induced peak Ca 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 influx, whereas either 2-APB or knockdown of TRPC6 blocked it. ACh-induced Ca influx was enhanced by PLC-δ1 overexpression, and was blocked partially by nifedipine and completely by 2-APB. TRPC-mediated Ca influx may be related to the enhanced Ca influx in PLC-δ1 overexpression.