I. Benz et al., PROPERTIES AND THE CYTOSKELETAL CONTROL OF CA-INDEPENDENT LARGE-CONDUCTANCE K+ CHANNELS IN NEONATAL RAT HIPPOCAMPAL-NEURONS(+), The Journal of membrane biology, 161(3), 1998, pp. 275-286
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.