CA2-ACTIVATED K+ CURRENTS IN NEURONS - TYPES, PHYSIOLOGICAL ROLES ANDMODULATION()

Action potentials in neurones are followed by a hyperpolarization, whi ch can last up to several seconds. This hyperpolarization has several phases that are mediated by the activation of different types of Ca2+- activated K+ currents. Patch-clamp studies have revealed two families of Ca2+-activated K+ channels of small (SKCa) and high (BKCa) conducta nce. Activation of BKCa channels contributes to action-potential repol arization, while SKCa channels are thought to underlie the afterhyperp olarization (AHP). In addition, AHPs in neurones can be divided into t wo distinct types that are easily separated by kinetic and pharmacolog ical criteria. It is now clear that only one type of AHP can be explai ned by activation of SKCa channels while a new type of Ca2+-activated K+ channel underlies the other. Modulation of this channel by a range of transmitters is a key determinant of the excitability of many neuro nes.