PROPERTIES AND THE CYTOSKELETAL CONTROL OF CA-INDEPENDENT LARGE-CONDUCTANCE K+ CHANNELS IN NEONATAL RAT HIPPOCAMPAL-NEURONS(+)

A member of the family of Ca++-independent large conductance K+ channe ls (termed BK channels) was identified in patch clamp experiments with cultured neonatal rat hippocampal neurons. permeation was characteriz ed (at 5 mmol/l external, 140 mmol/l internal KC; 135 mmol/l external Na+) by a conductance of 107 pS, a ratio P-Na/P-K - 0.01, and outward rectification near the reversal potential. Channel activity was not vo ltage-dependent, could not be reduced by internal TEA or by a shift of internal pH from 7.4 to 6.8, i.e., discriminating features within the Ca++-independent BK channel family. Cytosolic proteolysis abolished t he functional state of hippocampal Ca++-independent BK channels, in co ntrast to the pronase resistance of hippocampal Ca++-activated BK chan nels which suggests structural dissimilarities between these related c hannels. Cytoskeletal alterations had an activating influence on Ca++- independent BK channels and caused a 3-4-fold rise in P-o but patch ex cision and channel isolation from the natural environment provoked the strongest increase in P-o, from 0.07 +/- 0.03 to 0.73 +/- 0.04. This activation process operated slowly, on a minute time scale and can be most easily explained with the loss of a membrane-associated inhibitor y particle. Once activated, Ca++-independent BK channels reacted sensi tively to a Mg-ATP supplemented brain tissue extract with a P-o declin e, from 0.60 +/- 0.06 to 0.10 +/- 0.05. Heated extracts failed to indu ce significant channel inhibition, providing evidence for a heat-unsta ble molecule with reassociates with the internal channel surface to re establish channel inhibition. A dualistic channel control, by this mem brane-associated molecule and by the cytoskeleton seems possible.