Meeting Abstract
The freshwater crustacean, Daphnia Magna, was exposed to 100 μmol concentration of 8-bromo-cAMP or 8-bromo-cGMP using a profusion system that administered the chemical messenger analog at a rate of 1.5 mL/sec. We hypothesized that the heart rate of Daphnia Magna would increase to the way cyclic nucleotides modulate the heart rate of the myogenic hearts of vertebrates. Daphnia Magna were pinned in place using cactus spines and allowed to equilibrate for 20 minutes before data collection. Heart rate was measured by taking a control heart rate before administering the chemical and compared to the heart rates at 5, 10, 15 and 20 min intervals after exposure. During each time interval, we took a 15-second video (100 frames/second) recording using an inverted microscope at 40x magnification that was equipped with recording capabilities. Heart rates were then determined in beats per minute by counting each systole during the 15-second video recording. Our results yielded a statistically significant inhibition of heart rate, compared to controls, when exposed to cAMP during the 15 and 20-minute time intervals and cGMP during the 10, 15 and 20 min time intervals. (P value of less 0.01 for cAMP and 0.05 for the 10 min and 0.01 for the 15 and 20 min intervals for cGMP; repeated measures non-parametric ANOVA). We concluded that both cAMP and cGMP play a significant role in determining heart rate of Daphnia Magna that is opposite of hypothesis. After 20 minutes of exposure to cAMP Daphnia Magna had a decreased heart rate by 30.4% from the control mean and cGMP decreased heart rate by 21.8% from the control mean. We are currently investigating if cyclic nucleotides have a positive inotropic effect and if the modulation of chronotropic effects of cyclic nucleotides is concentration dependent.
