Effects of siRNA knock-down of TRPC6 and InsP(3)R1 in vasopressin-induced Ca(2+) oscillations of A7r5 vascular smooth muscle cells.
We used post-transcriptional gene silencing (with small interfering RNA) to examine specifically the roles of Type 1 inositol tris-phosphate receptors (InsP(3)R1) and transient receptor potential channel 6 (TRPC6) in Ca(2+) oscillations induced by arginine vasopressin (AVP), a typical G-protein coupled receptor agonist. Ca(2+) oscillations were observed in individual A7r5 cells with confocal imaging of fluo-4 fluorescence, and SR-releasable Ca(2+) was assessed by exposure to cyclopiazonic acid (CPA). In control cells, both AVP (100 nM) and a direct activator of TRPC6 (OAG, l-oleoyl-2-acetyl-glycerol, 100 microM) caused Ca(2+) oscillations in the majority of cells (e.g. AVP: 85%, 0.97+/-0.05/min; OAG: 83%, 1.00+/-0.07/min). Partial knock-down of TRPC6 (to <27% protein expression) was more effective than partial knock-down of InsP(3)R1 (to <30% protein expression) in reducing the fraction of cells that produced Ca(2+) oscillations in response to AVP or OAG (22% and 83% of cells showing oscillations, respectively, in response to AVP; 31% and 72% of cells showing oscillation, respectively, in response to OAG). CPA-induced SR Ca(2+) release was unaffected by siRNA transfection. Inhibition of InsP(3)R with Xestospongin C abolished both AVP and OAG-induced Ca(2+) oscillations. Nifedipine (10 microM) had no effect. The key results, including the effects of partial (as opposed to complete) knock-down of InsP(3)R1 and TRPC6, and the (unexpected) finding of OAG-induced Ca(2+) oscillations, are predicted by a canonical mathematical model of Ca(2+) oscillations in which InsP(3)R1 functions as the SR Ca(2+) release channel and TRPC6 as the receptor-operated Ca(2+) influx channel. These results indicated that TRPC6 functioning as a major type of receptor-operated Ca(2+) channel played a critical role in Ca(2+) oscillations of A7r5 cells' response to AVP or OAG, and partial knock-down of TRPC6 was more effective than partial knock-down of InsP(3)R1 in reducing Ca(2+) oscillations.
Department of Physiology, School of Medicine, University of Maryland, 655 West Baltimore Street, Baltimore, MD 21201, United States. manxiangli@hotmail.com
Manxiang
M
Li
Joseph
J
Zacharia
Xiuzhen
X
Sun
Withrow Gil
WG
Wier
D000818:Animals; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects*; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects*; D011247:Pregnancy; D034741:RNA, Small Interfering / Q000494:pharmacology*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D050052:TRPC Cation Channels / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*; D014162:Transfection; D014667:Vasopressins / Q000494:pharmacology*
D053496:Inositol 1,4,5-Trisphosphate Receptors; D034741:RNA, Small Interfering; D050052:TRPC Cation Channels; C492145:Trpc6 protein, rat; D014667:Vasopressins