In a number of molluscs belonging to different groups, serotonin and b
eta-adrenergic agonists have a stimulatory effect on the sarcolemmal a
denylyl cyclase (AC) activity, which is potentiated by guanine nucleot
ides. Catecholamines (isoprotenerol > adrenaline > noradrenaline) inhi
bit AC activity in Anodonta cygnea sarcolemma. In muscle membranes of
Anodonta, Mizuhopectin and Spisula, a serotonin receptor (5-HTR) and a
beta-adrenoreceptor (beta-AR) were identified. Guanine nucleotides lo
wered the affinities of 5-HTR and beta-AR to agonists.