Meeting Abstract
Weakly electric fish generate electric organ discharges (EODs) to navigate and communicate. The EOD waveform is determined by the morphology and subcellular localization of ion channels in the electric organ cells (electrocytes). To understand the role of electrocyte morphology and ion channel localization in shaping the EOD waveform, we used two-photon confocal microscopy to image electrocytes and immunohistochemistry to localize ion channels, ion transporters and Na+/K+ ATPases in Eigenmannia virescens. We found that electrocytes are highly polarized cylindrical cells ~1 mm in length and ~600 µm in diameter. The posterior face is deeply invaginated and vascularized with dense layers of vesicles beneath the membrane, while the main body and anterior face are relatively smooth. These cells initiate the AP with cholinergic receptors and voltage-gated sodium (Nav) channels localized only on the posterior face, and terminate the AP with sodium activated potassium (KNa) channels which are restricted to the anterior face. The extreme compartmentalization of KNa channels and Nav channels observed here is very different from mammalian neurons where KNa channels are closely clustered with Na+ channels in microdomains. Computational simulations of electrocyte AP and sodium dynamics suggest that KNa channels might be activated by lower Na+ concentrations than in mammalian neurons. To determine whether electrocyte KNa channels have higher sensitivity to Na+ ions, we cloned the slack gene which encodes the KNa channel in electrocytes. Alignment of amino acid sequences of the slack channels expressed among E.virescens electrocytes and mammalian neurons shows amino acid substitutions in the sodium regulatory sites in electrocytes.
