Control of Cnida Discharge: II. Microbasic p-Mastigophore Nematocysts are Regulated by Two Classes of Chemoreceptors

Using tentacles of the sea anemone, Aiptasia pallida, Thorington and Hessinger ( 1984, 1988a, b) recently identified two classes of Chemoreceptors involved in sensitizing cnidocytes to discharge cnidae in response to mechanical stimuli. Discharge of cnidae was quantified by measuring adhesive force between the tentacles and a test object. This measurement is assumed to reflect the contribution of the three types of cnidae present in the tentacles of A. pallida: the adherent spirocysts and two types of penetrant nematocysts, the predominant microbasic p-mastigophores and the basotrichous isorhizas. In the present paper we directly measure the dis charge of the microbasic p-mastigophores and show that mastigophore-containing cnidocytes are sensitized by representative agonists for these two classes of Chemoreceptors. We also show that under certain conditions the number of discharged microbasic p-mastigophores correlates linearly to a major component of the measured adhesive force. This enables us to calculate the contribution to adhesive force made by individual mastigophores.