MECHANOELECTRIC TRANSDUCTION IN NEMATOCYTES OF A HYDROPOLYP (CORYNIDAE)

In sensitivity and ultrastructure of their cnidocil apparatus (CA), th e nematocytes (stinging cells) of hydrozoans are analogous to hair cel ls of vertebrates and epidermal mechanoreceptors of insects. Intracell ular recordings using current and voltage clamp in the capitate tentac les of the marine hydropolyp Stauridiosarsia producta (Corynidae) now revealed that depolarizing receptor potentials and receptor currents a re generated in nematocytes (stenotele type) in response to mechanical stimulation of the CA. The responsive cells were identified by inject ion of Lucifer Yellow. For recording, the tentacles were isolated from the polyp and held by a suction capillary. Stimuli were applied by a glass probe moved electromagnetically or piezoelectrically. The mechan osensitivity of the nematocytes was found to be strictly limited to th e CA. The characteristics of the mechanoelectric transduction were tho se typical of mechanoreceptor cells: phasic-tonic time course of an in crease in membrane conductance; latency between stimulus and receptor response < 50 mu s; sigmoid relationship between receptor-response amp litude and stimulus amplitude; maximal increase in conductance of grea ter than or equal to 15 nS; reversal potential between + 35 mV and - 1 0 mV; unspecific cation dependence and reversible blocking by streptom ycin. The results suggest a direct mechanical control of unspecific ca tion channels such as has been found for mechanoreceptor cells. Suprat hreshold receptor potentials elicit two forms of regenerative depolari zation: non-inactivating, steplike potentials and action potentials. T he latter can trigger discharge of the nematocyst.