EFFECT OF TEMPERATURE ON BRADYKININ-INDUCED ARACHIDONATE RELEASE AND CALCIUM MOBILIZATION IN VASCULAR ENDOTHELIAL-CELLS

The effect of decreased temperature on Ca2+-dependent arachidonic acid release was studied in vascular endothelial cells by investigating bradykinin (BK)-stimulated Ca2+ mobilization, inositol phosphate formation and arachidonic acid release. At both 37-degrees-C and 22-degrees-C, BK efficiently increased cytosolic Ca2+ concn. ([Ca2+]i). At 22-degrees-C, peak [Ca2+]i was higher and returned to basal levels more slowly. Although this response was preceded by rapid formation of Ins(1,4,5)P3, the activity of phospholipase C was significantly impaired at 22-degrees-C. To determine if Ins(1,4,5)P3 effectively mobilized intracellular Ca2+, we used saponinpermeabilized cells. Ins(1,4,5)P3 mobilized sequestered Ca2+ to a similar degree at 37-degrees-C and 22-degrees-C, although Ca2+ release was prolonged at 22-degrees-C. In intact cells, BK mobilized intracellular Ca2+ stores and activated Ca2+ entry. The rate of Ca-45(2+) entry was approx. 2-fold slower at 22-degrees-C, even though the peak and duration of the rise in [Ca2+]i were higher and sustained at the lower temperature. TG mobilized intracellular Ca2+, activated Ca2+ entry and elevated [Ca2+]i at both temperatures. As with BK, the peak [Ca2+]i reached after thapsigargin treatment was higher at 22-degrees-C. This effect of lower temperature on [Ca2+]i was most probably due to decreased Ca2+ efflux after a decrease in activity of the Ca2+-ATPase on the plasma membrane. Both A23187 and BK were shown to stimulate phospholipase A2 and arachidonic acid release at 22-degrees-C. In each case, the rate and extent of release were decreased compared with that at 37-degrees-C. Among several effects, lowering the temperature decreases the activity of phospholipase C, Ca2+-ATPase(s), Ca2+-entry mechanisms and phospholipase A2. Together, these effects lead to a higher and more prolonged elevation of [Ca2+]i, but a decrease in arachidonate release in response to BK.