Differential distribution of SK channel subtypes in the brain of the weakly electric fish Apteronotus leptorhynchus

Calcium signals in vertebrate neurons can induce hyperpolarizing membrane responses through the activation of Ca 2+ ‐activated potassium channels. Of these, small conductance (SK) channels regulate neuronal responses through the generation of the medium after‐hyperpolarization (mAHP). We have previously shown that an SK channel ( Apt SK2) contributes to signal processing in the electrosensory system of Apteronotus leptorhynchus . It was shown that for pyramidal neurons in the electrosensory lateral line lobe (ELL), Apt SK2 expression selectively decreases responses to low‐frequency signals. The localization of all the SK subunits throughout the brain of Apteronotus then became of substantial interest. We have now cloned two additional SK channel subunits from Apteronotus and determined the expression patterns of all three AptSK subunits throughout the brain. In situ hybridization experiments have revealed that, as in mammalian systems, the Apt SK1 and 2 channels showed a partially overlapping expression pattern, whereas the Apt SK3 channel was expressed in different brain areas. The Apt SK1 and 2 channels were the primary subunits found in the major electrosensory processing areas. Immunohistochemistry further revealed distinct compartmentalization of the Apt SK1 and 2 channels in the ELL. Apt SK1 was localized to the apical dendrites of pyramidal neurons, whereas Apt SK2 channels are primarily somatic. The distinct expression patterns of all three Apt SK channels may reflect subtype‐specific contributions to neuronal function, and the high homology between subtypes from a number of species suggests that the functional roles for each channel subtype are conserved from early vertebrate evolution. J. Comp. Neurol. 507:1964–1978, 2008. © 2008 Wiley‐Liss, Inc.