Pharmacological profile of store-operated channels in cerebral arteriolar smooth muscle cells

1 In this study, we determined a pharmacological profile of store-operated channels (SOCs) in smooth muscle cells of rabbit pial arterioles. Ca2+-indicator dyes, fura-PE3 or fluo-4, were used to track [Ca2+](i) and 10 muM methoxyverapamil (D600) was present in all experiments on SOCs to prevent voltage-dependent Ca2+ entry. Store depletion was induced using thapsigargin or cyclopiazonic acid. 2 SOC-mediated Ca2+ entry was inhibited concentration dependently by Gd3+ (IC50 101 nM). It was also inhibited by 10 muM La3+ (70% inhibition, N = 5), 100 muM Ni2+ (57% inhibition, N = 5), 75 muM 2-aminoethoxydiphenylborate (66% inhibition, N = 4), 100 mM capsaicin (12% inhibition, N = 3) or preincubation with 10 muM wortmannin (76% inhibition, N = 4). It was completely resistant to 1 mum nifedipine (N = 5), 10 muM SKF96365 (N = 6), 10 muM LOE908 (N = 14), 10-100 muM ruthenium red (N = 1+2), 100 muM sulindac (N = 4), 0.5 mM streptomycin (N = 3) or 1 : 10,000 dilution Grammostolla spatulata venom (N = 4). 3 RT-PCR experiments on isolated arteriolar fragments showed expression of mRNA species for TRPC1, 3, 4, 5 and 6. 4 The pharmacological profile of SOC-mediated Ca2+ entry in arterioles supports the hypothesis that these SOCs are distinct from tonically active background channels and several store-operated and other nonselective cation channels described in other cells. Similarities with the pharmacology of TRPC1 support the hypothesis that TRPC1 is a subunit of the arteriolar smooth muscle SOC.