COLOCALIZATION OF ACTIVE KCA CHANNELS AND CA2+ CHANNELS WITHIN CA2+ DOMAINS IN HELIX NEURONS

Large conductance Ca2+-activated K+ channels (KCa channels) have to be colocalized with Ca2+ channels to be involved in nerve cell firing re gulation. KCa channels were detected in cell-attached patches performe d in voltage-clamped Helix neurons. This technique allowed Ca2+ entry to occur either within or around the patch. We observed that the subme mbrane Ca2+ diffusion was sufficiently limited to prevent the KCa chan nels from being opened by remote Ca2+ entry. The KCa channels located i n areas devoid of Ca2+ channels remained quiescent during cell firin g. These crypto channels were detected following either patch excision or intracellular Ca2+ injection. These data provide direct evidence f or the existence of functional Ca2+ domains in a nonspecialized neural membrane.