Rat supraoptic magnocellular neurones show distinct large conductance, Ca2+-activated K+ channel subtypes in cell bodies versus nerve endings
Dopico, Alejandro M. ; Widmer, Helene ; Wang, Gang ; Lemos, Jose R. ; Treistman, Steven N.
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UMass Chan Affiliations
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Keywords
Animals
*Benzylisoquinolines
Calcium
Calcium Channel Blockers
Evoked Potentials
Ion Channel Gating
Large-Conductance Calcium-Activated Potassium Channels
Male
Nerve Endings
Neurons
Patch-Clamp Techniques
Potassium Channels
*Potassium Channels, Calcium-Activated
Rats
Reaction Time
Supraoptic Nucleus
Biochemistry
Physiology
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Abstract
1. Large conductance, Ca2+-activated K+ (BK) channels were identified in freshly dissociated rat supraoptic neurones using patch clamp techniques. 2. The single channel conductance of cell body BK channels, recorded from inside-out patches in symmetric 145 mM K+, was 246.1 pS, compared with 213 pS in nerve ending BK channels (P1.53 microM for the neurohypophysial channel, indicating the higher Ca2+ sensitivity of the cell body isochannel. 5. Cell body BK channels showed fast kinetics (open time constant, 8.5 ms; fast closed time constant, 1.6 and slow closed time constant, 12.7 ms), identifying them as 'type I' isochannels, as opposed to the slow gating (type II) of neurohypophysial BK channels. 6. Cell body BK activity was reduced by 10 nM charybdotoxin (NPo, 37% of control), or 10 nM iberiotoxin (NPo, 5% of control), whereas neurohypophysial BK channels are insensitive to charybdotoxin at concentrations as high as 360 nM. 7. Whilst blockade of nerve ending BK channels markedly slowed the repolarization of evoked single spikes, blockade of cell body channels was without effect on repolarization of evoked single spikes. 8. Ethanol reversibly increased neurohypophysial BK channel activity (EC50, 22 mM; maximal effect, 100 mM). In contrast, ethanol (up to 100 mM) failed to increase cell body BK channel activity. 9. In conclusion, we have characterized BK channels in supraoptic neuronal cell bodies, and demonstrated that they display different electrophysiological and pharmacological properties from their counterparts in the nerve endings.
Source
J Physiol. 1999 Aug 15;519 Pt 1:101-14.