Studies on capacitative calcium entry in vascular smooth muscle cells by measuring 45CA2+ influx.
Capacitative calcium entry was studied in the A7r5 vascular smooth muscle cell line by measuring 45Ca2+ influx. Entry was induced by depletion of the Ca2+ pools by either the receptor agonist [Arg]8 vasopressin (AVP) or the SR-Ca(2+)-ATPase inhibitor thapsigargin (TG). TG showed a higher efficacy for calcium influx than AVP. This is probably due to a larger Ca2+ release from the pools induced by TG compared to AVP and the irreversible inhibition of the SR-Ca(2+)-ATPase by TG causing influx to persist for a longer period of time. At maximally effective concentrations signals induced by AVP and TG were synergistic in the absence but not in the presence of the intracellular calcium chelator, 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA). Depolarisation with 55 mM KCl completely inhibited 45Ca2+ influx induced by TG but only slightly the one induced by AVP, both effects being less pronounced in the presence of BAPTA. [Ca2+]c signals induced by AVP and TG were both inhibited by depolarisation. In conclusion, although our results show differences between AVP- and TG- induced Ca2+ influx, they can be explained by their different mechanism of action and are in accordance with an activation of the same capacitative entry pathway by both agents.
Skutella
M
M
Pharmacology Group, School of Pharmacy University of Lausanne, Switzerland.
Rüegg
U T
UT
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D019284:Thapsigargin / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D014662:Vasoconstrictor Agents; D001127:Arginine Vasopressin; D004533:Egtazic Acid; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium