Muscarine modulation by a G-protein alpha-subunit of delayed rectifier K+ current in rat ventromedial hypothalamic neurones.
1. Rat cultured ventromedial hypothalamic (VMH) neurones obtained from embryonic hypothalamus were used to study the muscarinic (carbachol) modulation of voltage-gated K+ currents with the whole-cell patch-clamp technique. 2. Carbachol produced a potent and concentration-dependent (100 fM to 100 microM) decrease of the outward delayed rectifier K+ current (IK) with an IC50 of 44 pM and a Hill coefficient of 0.4. The carbachol-induced depression of IK was reduced by pirenzepine (1-10 microM) and atropine (1 microM). Carbachol had no effect on the transient outward K+ current (IA). 3. Intracellular dialysis with guanosine 5'-O-(2-thiodiophosphate) (GDP-beta-S, 500 microM) significantly diminished the carbachol-induced depression of IK, suggesting GTP-binding protein (G-protein) involvement. Pre-incubation of VMH neurones with pertussis toxin (200-400 ng ml-1) or cholera toxin (1 microgram ml-1) for 24-48 h had no effect on the carbachol-induced depression of IK. This suggested that the G alpha o, G alpha i, and G alpha s G-protein alpha-subunits were not involved in mediating the carbachol-induced depression of IK in VMH neurones. 4. Treatment (24-48 h) of VMH neurones with antisense phosphothio-oligodeoxynucleotides to the G alpha 11 G-protein subunit (10 microM) significantly diminished the carbachol-induced depression of IK. Treatment with 10 microM of either G alpha 11 sense or antisense to G alpha q had no effect. 5. These results demonstrate a novel and potent muscarinic depression of IK in VMN neurones, and that this depression is specifically mediated by the G alpha 11 G-protein subunit.(ABSTRACT TRUNCATED AT 250 WORDS)
ffrench-Mullen
J M
JM
Department of Pharmacology, Zeneca Pharmaceuticals Group, Zeneca Inc., Wilmington, DE 19897.
Plata-Salamán
C R
CR
Buckley
N J
NJ
Danks
P
P
D000818:Animals; D001483:Base Sequence; D002217:Carbachol / Q000494:pharmacology; D004247:DNA; D004594:Electrophysiology; D005260:Female; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000378:metabolism*; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D015221:Potassium Channels; D011976:Receptors, Muscarinic; D002217:Carbachol; D004247:DNA; D019204:GTP-Binding Proteins; D011188:Potassium