Small conductance calcium-activated potassium channels of trout CNS: molecular structure, developmental expression, and partial biophysical characterization.
Two small conductance calcium-activated potassium channels that exhibited amino acid similarity with mammalian SK2 and SK3, respectively, were PCR cloned from the CNS of trout and sequenced. Upon heterologous expression in Sf21 insect cells trout SK2 (termed tSK2) produced a calcium-dependent, voltage-insensitive, and non-inactivating current with a single unit conductance of about 11 pS. This current was half maximally activated by 0.76 microM Ca(2+) and blocked by picomolar concentrations of apamin but not by TEA. Transcripts of both SK-related channels possessed a widespread distribution in the mature brain tissue of trout and outside the nervous system were detectable in muscle tissue as well as in liver. As revealed by RT-PCR analysis transcripts encoding tSK2 and tSK3 channels were early detectable during brain development (stage 30, shortly after hatching).