Uptake characteristics of the InsP3-sensitive and -insensitive Ca2+ pools in porcine aortic smooth-muscle cells: different Ca2+ sensitivity of the Ca2(+)-uptake mechanism.
We have investigated the Ca2(+)-uptake characteristics of the InsP3-sensitive and -insensitive non-mitochondrial Ca2+ pools in permeabilized cultured porcine aortic smooth-muscle cells. The InsP3-sensitive Ca2+ pool, which was also GTP sensitive, had a high Ca2+ affinity and was highly oxalate permeable. The InsP3-insensitive Ca2+ store, which was also GTP insensitive, had a much lower Ca2+ affinity and presented a low oxalate permeability. The loading of both pools decreased at high free [Ca2+], although these cells did not have a Ca2(+)-induced Ca2+ release mechanism. This decreased loading of the InsP3-sensitive Ca2+ pool at higher free [Ca2+] must be taken into consideration when investigating a possible Ca2(+)-inhibition of the InsP3-induced Ca2+ release. Part of the Ca2+ uptake into the InsP3-insensitive Ca2+ pool was not affected by the Ca2(+)-pump inhibitors vanadate, thapsigargin and 2,5-di-(tert-butyl)-1,4-benzohydroquinone.
Missiaen
L
L
Department of Physiology, K.U.Leuven, Belgium.
De Smedt
H
H
Droogmans
G
G
Declerck
I
I
Plessers
L
L
Casteels
R
R
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D013552:Swine; D014638:Vanadates / Q000494:pharmacology
D002132:Calcium Radioisotopes; D000001:Calcimycin; D014638:Vanadates; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium