Basal calcium entry in vascular smooth muscle.
Basal calcium leak into smooth muscle was identified 30 years ago yet remains poorly understood. We characterized this leak measuring 45Ca2+ uptake into cultured rat aortic smooth muscle cells. Wash solution (0 degrees C) containing lanthanum (3 mM) removed extracellular tracer and increased cellular 45Ca2+ retention more effectively than EGTA (0.2 mM). Basal Ca2+ entry was 1.45 x 10(9) Ca2+ x cell(-1) x min(-1). This translated to approximately 250 micromol(-1) x min(-1) given cell volumes of 4-15 pl as determined by 3-D image reconstruction. Gadolinium (100 microM) blocked 80% of the leak and exhibited a biphasic concentration-response relation (IC50s=1 microM and 2 mM). Organic ion channel blockers also inhibited approximately 80% of the leak; 45% by nifedipine (10 microM), 7% was exclusively blocked by SKF 96365 (1-[b-[3-(4-Methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole) (50 microM) and 23% was exclusively sensitive to 2-aminoethoxy-diphenylborate (2-APB, 75 microM). Reverse transcriptase polymerase chain reaction revealed TrpC1, 4 and 6 mRNA, and we propose that 2-APB may selectively block TrpC4-containing channels. We conclude that basal Ca2+ entry is mainly due to a basal open probability of excitable Ca2+ -channels.
Poburko
Damon
D
Group of Pharmacology, School of Pharmacy, Universities of Geneva and Lausanne, 1015 Lausanne, Switzerland. dpoburko@interchange.ubc.ca
Lhote
Philippe
P
Szado
Tania
T
Behra
Tasneim
T
Rahimian
Roshanak
R
McManus
Bruce
B
van Breemen
Cornelis
C
Ruegg
Urs T
UT
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000235:genetics; D002132:Calcium Radioisotopes; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics; D009543:Nifedipine / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011921:Rats, Inbred WKY; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050825:Synaptosomal-Associated Protein 25; D050052:TRPC Cation Channels
D001896:Boron Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002132:Calcium Radioisotopes; D007093:Imidazoles; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D050052:TRPC Cation Channels; C096351:transient receptor potential cation channel, subfamily C, member 1; D049452:Green Fluorescent Proteins; D004533:Egtazic Acid; D007811:Lanthanum; D005682:Gadolinium; C109986:2-aminoethoxydiphenyl borate; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D009543:Nifedipine; D002118:Calcium