Muscarinic inhibition of M-current and a potassium leak conductance in neurones of the rat basolateral amygdala.
1. Voltage-clamp recordings using a single microelectrode were obtained from pyramidal neurones of the basolateral amygdala (BLA) in slices of the rat ventral forebrain. Slow inward current relaxations during hyperpolarizing voltage steps from a holding potential of -40 mV were identified as the muscarinic-sensitive M-current (IM), a time- and voltage-dependent potassium current previously identified in other neuronal cell types. 2. Activation of IM was voltage dependent with a threshold of approximately -70 mV. At membrane potentials positive to this, the steady-state current-voltage (I-V) relationship showed substantial outward rectification, reflecting the time- and voltage-dependent opening of M-channels. The underlying conductance (gM) also increased sharply with depolarization. 3. The reversal potential for IM was -84 mV in medium containing 3.5 mM K+. This was shifted positively by 27 mV when the external K+ concentration was raised to 15 mM. 4. The time courses of M-current activation and deactivation were fitted by a single exponential. The time constant for IM decay, measured at 24 degrees C, was strongly dependent on membrane potential, ranging from 330 ms at -40 mV to 12 ms at -100 mV. 5. Bath application of carbachol (0.5-40 microM) inhibited IM, as evidenced by the reduction or elimination of the slow inward M-current relaxations evoked during hyperpolarizing steps from a holding potential of -40 mV. The outward rectification of the steady-state I-V relationship at membrane potentials positive to -70 mV was also largely eliminated. The inhibition of IM by carbachol was dose dependent and antagonized by atropine. 6. Carbachol produced an inward current shift at a holding potential of -40 mV that was only partially attributable to inhibition of IM. An inward current shift was also produced by carbachol at membrane potentials negative to -70 mV, where IM is inactive. These effects were dose dependent and antagonized by atropine. They were attributed to the muscarinic inhibition of a voltage-insensitive potassium leak conductance (ILeak). 7. In most cells, carbachol reduced the slope of the instantaneous I-V relationship obtained from a holding potential of -70 mV so that it crossed the control I-V plot at the reversal potential for ILeak. This was found to be -108 mV in 3.5 mM K+ saline, shifting to -66 mV in 15 mM K+ saline.(ABSTRACT TRUNCATED AT 400 WORDS)
Womble
M D
MD
Department of Physiology, University of Michigan Medical School, Ann Arbor 48109-0622.
Moises
H C
HC
D000679:Amygdala / Q000187:drug effects*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D010277:Parasympathomimetics / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*
D010277:Parasympathomimetics; D015221:Potassium Channels; D001285:Atropine; D002217:Carbachol; D000254:Sodium-Potassium-Exchanging ATPase