Ion channels and transporters in the electroreceptive ampullary epithelium from skates

Abstract

Two ampullary epithelial properties necessary for electroreception were used to identify the types of ion channels and transporters found in apical and basal membranes of ampullary receptor cells of skates and to assess their individual role under voltage-clamp conditions. The two essential properties are (1) a steady-state negative conductance generated in apical membranes and (2) a small, spontaneous current oscillation originating in basal membranes (Lu and Fishman, 1995). The effects of pharmacological agents and ion substitutions on these properties were evaluated from transorgan or transepithelial complex admittance determinations in the frequency range 0.125 to 50 Hz measured in individual, isolated ampullary organs. In apical membranes, L-type Ca channels were found to be responsible for generation of the steady-state negative conductance. In basal membranes, K and Ca-dependent Cl (Cl(Ca)) channels were demonstrated to contribute to a net positive membrane conductance. L-type Ca channels were also evident in basal membranes and are thought to function in synaptic transmission from the electroreceptive epithelium to the primary afferent nerve. In addition to ion channels in basal membranes, two transporters (Na+/K+ pump and Na(+)-Ca+ exchanger) were apparent. Rapid (minutes) cessation of the current oscillation after blockage of any of the basal ion channels (Ca, Cl(Ca), K) suggests critical involvement of each of these channel types in the generation of the oscillation. Suppression of either Na+/K+ transport or Na(+)-Ca2+ exchange also eliminated the oscillation but at a slower rate, indicating an indirect effect.

Resting potential of excitable neuroblastoma cells in weak magnetic fields

“…Therefore, within the limitation imposed by the sensitivity of our system, the results are reasonably sufficient to exclude the possibility that EMF detection as reflected in changes in resting membrane potential or transmembrane current is a general property of excitable cells in culture. Our conditions of measurement were such that we would have seen changes as small as about 38 mV, which is in the range of sensitivity of the electrosensory cells in fishes (10-100 mV) [23]. It appears, therefore, that the mechanism in the lower vertebrates that confers electrosensitivity is not present in 5Y cells.…”

Androgen-Induced Changes in the Response Dynamics of Ampullary Electrosensory Primary Afferent Neurons

“…These changes in the current kinetics of electrocytes are thought to result from the differential expression of multiple channels (e.g., Na ϩ and/or K ϩ ) genomically regulated by androgens (Zakon, 1996(Zakon, , 1998. Previous work on ampullary electroreceptors implicates Ca ϩ2 and K ϩ currents, but not Na ϩ , in the tuning mechanism of electroreceptors (Clusin and Bennett, 1979;Lu and Fishman, 1995b) and in the hair cell receptors of other less recently derived vertebrates (Crawford and Fettiplace, 1981). Similar androgen-induced changes to these currents may also affect the current kinetics of electroreceptor cells and their frequency tuning.…”

Electroreception in marine fishes: chondrichthyans

“…Ca 2+ influx leads to the efflux of K + ions though Ca‐gated K + channels that deactivates the Ca 2+ channels along the entire membrane and repolarises the cell (Bennett & Obara, ; Clusin & Bennett, ; Clusin & Bennett, ). A complex interplay between L‐type Ca 2+ channels in the apical membrane and K and Ca‐dependent Cl‐ channels in the basolateral membrane maintains a balance between membrane conductance and current oscillation that results in signal amplification and high sensitivity across the electrosensory epithelium (Lu & Fishman, , ). The sensory tuning of electroreceptors is dictated, in part, by the molecular structure of the ion channels embedded within the excitable membranes of the sensory cells.…”