Docozsahexaenoic acids activate large conductance calcium- Activated potassium channels via phospholipase C-inositol triphosphate- calcium pathway in normal rat coronary smooth muscle cells

Objective To investigate the mechanisms of docosahexaenoic acids ( DHA ) on activating large conductance calcium- Activated potassium channels ( BK channels) in normal rat coronary smooth muscle cells. Methods Normal coronary smooth muscle cells were isolated by enzyme digestion from Sprague-Dawley rats. BK currents were recorded by patch clamp in whole cell and single channel configurations, respectively. The effects of DHA on cytosolic calcium concentrations were examined by recording the changes of fluorescence intensity ratios. Results DHA ( 1 μmol/1,) could activate BK channels. Open probabilities (NP0) of BK channels at test potential 60 mV, and calcium concentrations in external solution at 0, 0. 01, 0. 1, 1, 3, 10, 50 and 100 μmol/L were 0. 002 7 ± 0. 000 4, 0. 006 0 ± 0.001 4, 0.097 2 ±0.010 6, 0. 137 9 ±0.032 9, 0.468 7 ±0. 163 7, 2.097 1 ±0. 310 4 and 3. 120 4 ± 0. 242 7, respectively ( P < 0. 05 , n = 4 ) . Before DHA perfusion, the fluorescence intensity ratio was 0.51 ±0.01, and the ratios were 0.53 ±0.02 and 0.55 ±0.01 after 0.001 and 0.01 (xmol/L DHA perfusion, respectively ( P > 0. 05 , n >5). The ratios were 0. 64 ± 0. 01 , 0. 65 ± 0. 01 , 0. 70 ± 0. 01, 0. 69 ±0.01, 0.68 ±0.01 and 0.67 ±0.02 after 0.1, 0.3, 1, 3, 5 and 10 μmol/L DHA perfusion, respectively, and EC50 was (0. 04 ± 0. 02) μmol/L( P < 0. 05 , n>4). They were all higher than that before DHA perfusion. After incubating with phospholipase C (PLC) blocker U73122 and inositol triphosphate ( IP3) blocker 2-APB, the ratios were 0. 52 ± 0. 01 and 0. 49 ± 0. 02 on the setting of 0. 1 p.mol/L DHA, respectively. Compared with control group (0. 64 ±0. 01) , the ratios decreased after incubating with blockers (P<0.05, 4). Conclusions Docosahexaenoic acids can activate large conductance calcium- Activated potassium channels by the pathway of PLC-IP3-Ca2+ to increase cytosolic calcium concentration in normal coronary smooth muscle cells, dilate the coronary vessels and bestow protective effects on cardiovascular system.