Calcium uptake in vascular smooth muscle during exposure to NE

Calcium uptakes were determined in canine mesenteric and ulnar arteries and in rabbit abdominal aortas. All vessels were excised, cut into 1 mm rings, mounted at near in-situ circumferences on stainless steel holders, and run in triplicate. Calcium uptakes were carried out in HEPES-buffered PSS using 45Ca 5 sec uptake durations. Uptakes were quenched in 5 mM EGTA-O-Ca-PSS at 1-20C. Tissues were weighed and leached with 10 mM EDTA before counting with a liquid scintillation counter. Calcium uptakes were obtained first at resting conditions and then at successive 5 sec intervals throughout 90 sec exposure periods to various concentrations of NE. Resting Ca uptakes ranged from 0.15 to 0.30 nanomoles/sec/g tissue (wet). Peak Ca uptakes during exposure to 10-5M NE ranged from 0.5 to 0.8 nanomoles/sec/g tissue. Increases in rates of uptake occurred early in the exposure period to NE (within 5-10 sec) and did not appear to be associated only with the tonic phase of the response. These data provide evidence that increased Ca uptake by the cells occurs early in the response to NE. They also indicate that short-term Ca uptake determinations (5 sec) provide reliable estimates of calcium uptake occurring throughout the NE-induced contractile response