IN-VITRO INVESTIGATION OF ALPHA-AMYLASE RELEASE FROM THE DIGESTIVE CELLS OF THE BIVALVE MOLLUSK PECTEN-MAXIMUS - EFFECT OF 2ND-MESSENGERS AND BIOGENIC-AMINES

The (neuro)endocrine control of enzyme release from invertebrate diges tive cells remains poorly understood. A tissue dissociation procedure was developed to investigate the regulatory mechanisms of alpha-amylas e discharge from the cells of the stomach-digestive gland complex of t he scallop Pecten maximus. The validity of the experimental system was tested by increasing the intracellular concentration of second messen ger analogues (N-6,2'-o-dibutyryl-adenosine-3', 5' cyclic monophosphat e and the ionophore A23187) known to mimic the activity of naturally o ccurring secretagogues in vertebrates: N-6,2'-o-dibutyryl-adenosine-3' ,5' cyclic monophosphate increased the time and dose-dependent release of alpha-amylase in a similar way as in vertebrates. A23187 was also very effective in inducing enzyme discharge. Since the in vitro bioass ay was shown to be functional and because axon terminals were previous ly seen in close contact to alpha-amylase secreting cells, the effect of some classic neuro-transmitters was explored. Only the cholinergic agonist carbachol and dopamine evoked a secretory response. Maximal st imulation of alpha-amylase release was reached at 10(-5) mol.1(-1) car bachol; at the same concentration dopamine was less effective than car bachol. By contrast, serotonin was totally inactive. The in vitro bioa ssay should prove useful for the identification of regulatory molecule s involved in the control of enzyme discharge and to study stimulus se cretion coupling mechanisms in scallop digestive cells.