Modulation of the excitability of cholinergic basal forebrain neurones by K_ATP channels

Abstract

The expression of ATP-sensitive K + (K ATP ) channels by magnocellular cholinergic basal forebrain (BF) neurones was investigated in thin brain slice and dissociated cell culture preparations using a combination of whole-cell, perforated-patch and single-channel recording techniques. Greater than 95% of BF neurones expressed functional K ATP channels whose activation resulted in membrane hyperpolarization and a profound fall in excitability. The whole-cell K ATP conductance was 14.0 ± 1.5 nS and had a reversal potential of -91.4 ± 0.9 mV that shifted by 59.6 mV with a tenfold increase in [K + ] o . I KATP was inhibited reversibly by tolbutamide (IC 50 of 34.1 µM) and irreversibly by glibenclamide (0.3-3 nM) and had a low affinity for [ATP] i (67% reduction with 6 mM [MgATP] i ). Using perforated-patch recording, a small proportion of the conductance was found to be tonically active. This was weakly potentiated by diazoxide (0.1 mM extracellular glucose) but insensitive to pinacidil (≤500 µM). Single-channel K ATP currents recorded in symmetrical 140 mM K + -containing solutions exhibited weak inward rectification with a mean conductance of 66.2 ± 1.9 pS. Channel activity was inhibited by MgATP (>50 µM) and activated by MgADP (200 µM). The K + channels opener diazoxide (200-500 µM) increased channel opening probability (NP o ) by 486 ± 120% whereas pinacidil (500 µM) had no effect. In conclusion, the characteristics of the K ATP channels expressed by BF neurones are very similar to channels composed of SUR1 and Kir6.2 subunits. In the native cell, their affinity for ATP is close to the resting [ATP] i , potentially allowing them to be modulated by physiologically relevant changes in [ATP] i . The effect of these channels on the level of ascending cholinergic excitation of the cortex and hippocampus is discussed.

Simultaneous Release of Glutamate and Acetylcholine from Single Magnocellular “Cholinergic” Basal Forebrain Neurons

“…Thus, in previous experiments using these neurons in long-term culture, they showed the same electrophysiological properties as those reported for identified cholinergic BF neurons in situ (Allen and Brown, 1993;Sim and Allen, 1998) and released ACh from their processes (Allen and Brown, 1996). Furthermore, neurons isolated in the same manner, grown on the same substrate, and maintained in identical growth media as those used in the present experiments (albeit as mass cell cultures) expressed the cholinergic marker choline acetyltransferase as determined by singlecell PCR (Allen and Brown, 2004). In this respect, therefore, they belong to that class of BF neurons conventionally regarded as cholinergic.…”

“…A dissociated cell suspension of basal forebrain neurons was prepared as reported previously (Allen and Brown, 2004). Briefly, 12-to 14-d-old Sprague Dawley rat pups were anesthetized by chloroform inhalation before decapitation according to Home Office guidelines.…”

ATP-sensitive potassium currents reduce the PGE2-mediated enhancement of excitability in adult rat sensory neurons

“…The sensitization produced by PGE 2 may be reversed by the capacity of K ATP to hyperpolarize the resting membrane potential and/or increase the rheobase of the action potential firing; these actions would decrease the excitability. Consistent with the reduction in excitability by K ATP channels, Allen and Brown (2004) reported that in magnocellular cholinergic neurons of the basal forebrain, activation of K ATP produced hyperpolarization of the membrane with a concomitant reduction in excitability. Their results also suggested that K ATP was tonically active at rest.…”

“…In this regard, K ATP channels control the release of insulin from pancreatic β cells (Ashcroft et al 1984;Ashcroft and Gribble 1998;Miki et al 1999;Schwanstecher et al 1998;Seino 1999) and blood flow in muscle, heart, and kidney tissue (Ashcroft 1988;Nelson and Quayle 1995;Terzic et al 1995;Yokoshiki et al 1998). In neurons, activation of K ATP results in membrane hyperpolarization that reduces excitability (Yamada et al 2001;Allen and Brown 2004) and activation of presynaptic K ATP channels can directly modulate neurotransmitter release from nerve terminals (Deist et al 1992;Ohno-Shosaku et al 1992;Watts et al 1995;Ye et al 1997). …”

Neuroprotective role of ATP-sensitive potassium channels in cerebral ischemia

“…However, the primary role of K ATP channels in many other central neurons is not glucosensing [84,90,99] . For instance, basal activity of K ATP channels can affect neuronal excitability in non-glucosensing neurons [100,101] . In the dentate granule neurons in the mouse hippocampus, K ATP channels are expressed with a high density [84,99] .…”