Fig. 1. Effect of dopamine on the in vitro secretion of protein by the albumen gland. Basal protein secretion was quantified using a protein detection kit (line graph) or by collecting the medium around the albumen glands and analyzing secreted proteins by SDS-PAGE. Basal protein secretion was monitored for 60 min, then 10 µmol l^-1 dopamine was added for an additional 20 min. The major protein secreted by the albumen gland of Helisoma duryi is the 66 kDa glycoprotein subunit of Helisoma duryi albumen gland protein (HdAGP), which appears as a heavily stained band. Addition of dopamine induced a rapid increase in the amount of HdAGP released. Removal of the stimulus at 80 min caused HdAGP secretory rate to rapidly return to basal levels. Each point on the line graph represents the mean ± S.E.M. of 6–8 samples.