We have examined the effects of raising G protein concentration on the pharmacology of a series of agonist and antagonist ligands at the m1, m3, and m5 muscarinic subtypes using a functional assay. Overexpression of G(alpha q) induced constitutive activity of these receptors. The constitutive activity was reversed completely by every muscarinic antagonist tested, which indicates that they are a...

In hippocampal and other cortical neurons, action potentials are followed by a slow afterhyperpolarization (sAHP) generated by the activation of small-conductance Ca(2+)-activated K(+) channels and controlling spike frequency adaptation. The corresponding current, the apamin-insensitive sI(AHP), is a well known target of modulation by different neurotransmitters, including acetylcholine (via M(...

In this work, we studied the in vitro G-protein activation induced by muscarinic agonists using [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) autoradiographic methods to characterize the M(2) and M(4) muscarinic subtypes response. Thus, we describe a detailed characterization of the increases in [(35)S]GTPgammaS binding elicited by carbachol (Cch) and oxotremorine (OXO) (bin...

In the present work we have investigated which muscarinic (M) receptor subtype is responsible for the steroidogenic effect of muscarinic agonists in bovine zona fasciculata-reticularis (ZFR) cells in culture. Radioligand binding studies using the muscarinic antagonist [(3)H]quinuclidinyl benzilate ([(3)H]QNB) demonstrated binding sites of high affinity (K(d)=0.45 nM) and low capacity ( approxim...

Particulate fractions from fresh bovine corneal endothelium exhibited high affinity, specific binding by a potent muscarinic cholinergic radioligand, [3H]QNB. Particulate fraction binding sites exhibited half maximal binding at approximately 0.3 nM [3H]QNB and reached a maximal binding capacity of 820 fmoles/mg of protein at 3 nM [3H]QNB. Muscarinic cholinergic antagonists and agonists competed...

The hippocampal slice preparation was used to classify cholinergic effects in terms of muscarinic receptor subtypes (M1 or M2) and biochemical effector systems linked to these effects in CA1 pyramidal cells. Based on the action of the M1 antagonist pirenzepine and the M2 antagonist gallamine, the muscarinic-induced membrane depolarization and blockade of the afterhyperpolarization appear to res...

It is widely accepted that cholinergic activity at muscarinic receptors is required to maintain cognitive functions, including learning and memory. Memory domains are especially impaired in schizophrenia, which may explain difficulties in psychosocial rehabilitation of individuals with this illness. However, little is known about the mechanism of this impairment. To understand our current knowl...

The rat muscarinic acetylcholine receptor subtype 3 was modified by swapping the third intracellular loop with the corresponding region of a constitutively active mutant human beta2-adrenergic receptor and attaching Renilla reniformis luciferase to its C terminus. The chimeric fusion receptor displayed constitutive Gq- and Gs-coupled activity as demonstrated in nuclear factor of activated T cel...

The high-affinity muscarinic antagonist L-[3H]quinuclidinyl benzi-late (L-[3H]QNB) was used to label muscarinic acetylcholine receptors in the astrocyte-enriched fraction isolated from rat hippocampus. Analysis of the saturation and drug inhibition data showed that [3H]QNB binding in the astroglia fraction was saturable, of high affinity (Kd = 0.026 nM) and competitively inhibited by muscarinic...