MUSCARINIC MODULATION BY A G-PROTEIN ALPHA-SUBUNIT OF DELAYED RECTIFIER K+ CURRENT IN RAT VENTROMEDIAL HYPOTHALAMIC NEURONS

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-clam p technique. 2. Carbachol produced a potent and concentration-dependen t (100 fM to 100 mu M) decrease of the outward delayed rectifier K+ cu rrent (I-K) with an IC50 of 44 pM and a Hill coefficient of 0.4. The c arbachol-induced depression of I-K was reduced by pirenzepine (1-10 mu M) and atropine (1 mu M), Carbachol had no effect on the transient ou tward K+ current (I-A). 3. Intracellular dialysis with guanosine 5'-O- (2-thiodiophosphate) (GDP-beta-S, 500 mu M) significantly diminished t he carbachol-induced depression of I-K, suggesting GTP-binding protein (G-protein) involvement. Pre-incubation of VMH neurones with pertussi s toxin (200-400 ng ml(-1)) or cholera toxin (1 mu g ml(-1)) for 24-48 h had no effect on the carbachol-induced depression of I-K. This sugg ested that the G alpha(o), G alpha(i), and G alpha(s) G-protein alpha- subunits were not involved in mediating the carbachol-induced depressi on of I-K in VMH neurones. 4. Treatment (24-48 h) of VMH neurones with antisense phosphothio-oligodeoxynucleotides to the G alpha(11) G-prot ein subunit (10 mu M) significantly diminished the carbachol-induced d epression of I-K. Treatment with 10 mu M of either G alpha(11) sense o r antisense to G alpha(q), had no effect. 5. These results demonstrate a novel and potent muscarinic depression of I-K in VMN neurones, and that this depression is specifically mediated by the G alpha(11) G-pro tein subunit. This action of the G alpha(11) subunit also provides the first demonstration of an association between the G alpha(11) G-prote in subclass (a member of the G(q) class) and a neuronal membrane curre nt.