Role of calcium in contractile responses of calf cardiac vein during cooling

The effects of cooling (to 28°C) were studied on the responses induced by carbachol (10 -9 - 3 × 10 -4 M) and serotonin (5-HT, 10 -8 - 3 × 10 -4 M) in calf cardiac vein preparations and the role of calcium ions in these effects were analyzed. Ring preparations of veins obtained from calf hearts were suspended in organ baths containing 25 mL of Krebs-Henseleit solution, maintained at 37°C and continuously gassed with 95%O 2-5%CO 2. After a resting period, preparations were contracted with carbachol (10 -9 - 3 × 10 -4 M) and 5-HT (10 -8 - 3 × 10 -4 M) at 37°C. The same protocol was repeated at 28°C after the preparations were allowed to equilibrate at this temperature for 60 min. In order to analyze the role of calcium ions (Ca 2+) in the cooling-induced vascular response, concentration-response curves to carbachol and 5-HT were obtained in the presence of verapamil (10 -6 M), caffeine (3 × 10 -4 M), and Ca 2+ free medium in the presence of EGTA at 28°C. During cooling to 28°C, the EC 50 values, to carbachol and 5-HT were significantly higher than at 37°C. Cooling to 28°C in the presence of verapamil, caffeine or Ca 2+ free medium in the presence of EGTA increased the EC 50 values, to both carbachol and 5-HT. These results suggest that Ca 2+ plays an essential role in the cooling-induced changes of calf cardiac vein preparations treated with carbachol and 5-HT.