|MadSci Network: Zoology|
Hi Lizzie, I hope I can answer your question. Just like you, a daphnia’s heart will beat faster when it receives a dose of caffeine. Caffeine belongs to a class of compounds called methylxanthines and can block a receptor on the surface of heart muscle cells for adenosine. In fact, it is caffeine's blockade of the A1 adenosine receptor in the heart that causes the heart to pound after a significant caffeine dose. Caffeine and similar compounds also inhibit a class of enzymes known as cyclic nucleotide phosphodiesterases. These enzymes are, in part responsible for degrading a stimulatory signal produced when excitatory neurotransmitters activate different neurons in the central nervous system (CNS). Thus, when they are inhibited by caffeine, the stimulatory signal remains active for a longer period of time resulting in a greater sense of alertness (a CNS effect) but also a higher heart rate, blood pressure and respiratory rate. Take care, Terry
Try the links in the MadSci Library for more information on Zoology.