Properties and physiological function of Ca2+-dependent K+ currents in uniglomerular olfactory projection neurons

Ca2+-activated potassium currents [I-kappa(Ca)] are an important link between the intracellular signaling system and the membrane potential, which shapes intrinsic electro-physiological properties. To better understand the ionic mechanisms that mediate intrinsic firing properties of olfactory uniglomerular projection neurons (uPNs), we used whole cell patch-clamp recordings in an intact adult brain preparation of the male cockroach Periplaneta americana to analyze electrophysiological. In the insect brain, uPNs form the principal pathway from the antennal lobe to the protocerebrum, where centers for multimodal sensory processing and learning are located. In uPNs the activation of I-kappa(Ca) was clearly voltage and Ca2+ dependent. Thus under physiological conditions I-kappa(Ca) is strongly dependent on Ca2+ influx kinetics and on the membrane potential. The biophysical characterization suggests that I-kappa(Ca) is generated by big-conductance (BK) channels. A small-conductance (SK) channel-generated current could not be detected. I-kappa(Ca) was sensitive to charybdotoxin (CTX) and iberiotoxin (IbTX) but not to apamin. The functional role of I-kappa(Ca) was analyzed in occlusion experiments under current clamp, in which portions of I-kappa(Ca) were blocked by CTX or IbTX. Blockade of I-kappa(Ca) showed that I-kappa(Ca) contributes significantly to intrinsic electrophysiological properties such as the action potential waveform and membrane excitability.