Dopamine sensitive adenylate cyclase in planaria Dugesia gonocephala

Abstract

1. The adenylate cyclase activity present in the particulate fraction of planaria homogenates has been characterized.

2. The enzyme requires divalent cations (Mg²⁺), and a K_m for ATP of 0.58 at 30°C was measured.

3. GTP and Gpp(NH)p, in an optimal range of 10⁻⁴–10⁻⁵M, increase the enzymatic activity.

4. In the presence of GTP, dopamine stimulates the adenylate cyclase and its action is inhibited by dopaminergic antagonist.

5. Both D-1 and D-2 selective dopaminergic agonists stimulate the enzymatic activity and their action is selectively antagonized by D-1 and D-2 antagonists.

6. The high concentrations required for some D-1 and D-2 agents to be effective, suggest an only partial consistency with mammalian dopaminergic receptors.