Muscarinic receptor is coupled with a cation channel through a GTP‐binding protein in guinea‐pig chromaffin cells.

Abstract

SUMMARY1. The ionic current evoked by muscarinic receptor agonists was investigated in dispersed chromaffin cells of the guinea-pig adrenal medulla using the whole-cell version of the patch-clamp procedure.2. Muscarine or oxotremorine (0-03-10 #M) produced an inward current associated with an increase in current noise at a holding potential of -40 mV. The relationship between current and oxotremorine concentration fitted well to a rectangular hyperbole with an apparent dissociation constant (KA) of 0-23 JiM.3. The muscarinic antagonists pirenzepine (0-1 ftM) and AF-DX 116 (0 3 /LM) shifted the dose-response curve to the right in a parallel manner. Dissociation constants (KB) for pirenzepine and AF-DX 116 were estimated to be 50 and 70 nm, respectively.4. The current-voltage relation for the current induced by muscarine had a negative slope below -30 or -20 mV, and the current reversed its polarity at 0-4 + 0-8 mV (n = 4) in standard salt solution. Removal of Mg2+ or Ca2+ from the perfusate did not modify the muscarinic current-voltage relationship.5. When Na+ in the bath solution was replaced with Tris, the muscarinic current-voltage relationship shifted to the left (the hyperpolarizing direction); the current reversed its polarity at -18-7 + 1-2 mV in a solution containing 72 mM-Na+ (three cells) and at -57-5 + 2-7 mV in nominally Na+-free solution (three cells). When Ca21 was replaced by Mg2+, in Na+-free solution, an inward current was not evoked by muscarinic stimulation.6. Tetraethylammonium (TEA; 0-03-3 mM) reduced the muscarinic current at -40 mV, and the KD value was 0-34 mm with a Hill coefficient of 1. Barium (4 mM) reduced the current to 0-69 + 0-06 of control (n = 3).7. When the recording electrodes contained guanosine-5'-O-(3-thiophosphate) (GTPyS, 100 UM), an inward current developed at -55 mV during the first few minutes after breaking into the cell interior. This inward current was associated with

Mechanism of abnormal intestinal motility in inflammatory bowel disease: how smooth muscle contraction is reduced?

“…It has been suggested that the M2 receptor supports M3-mediated activity and indirectly contributes to smooth muscle contraction. However, more recent reports indicate that the M2 receptor can directly activate L-type Ca 2+ channels and nonselective cation channels via c-src, phosphoinositide 3-kinase (PI3K) and protein kinase C (PKC), and contribute to intestinal smooth muscle contraction (Inoue and Kuriyama, 1991;Wan et al, 1999;Jin et al, 2002).…”

“…It has been suggested that the M2 receptor supports M3-mediated activity and indirectly contributes to smooth muscle contraction. However, more recent reports indicate that the M2 receptor can directly activate L-type Ca 2+ channels and nonselective cation channels via c-src, phosphoinositide 3-kinase (PI3K) and protein kinase C (PKC), and contribute to intestinal smooth muscle contraction (Inoue and Kuriyama, 1991; Wan et al, 1999; Jin et al, 2002).In an acetic acid-induced dog ileitis model, acetylcholine-induced contraction of circular smooth muscle is decreased, but contraction of longitudinal smooth muscle is unchanged (Shi and Sarna, 1999). In a TNBS-induced guinea-pig ileitis model, although the contractile force of the circular smooth muscle in response to acetylcholine is decreased, the contractile force of the longitudinal smooth muscle is increased (Martinolle et al, 1997).…”

Localization of Muscarinic Receptor and Cation Channel in Guinea-Pig Adrenal Chromaffin Cells

“…This neuronal transmission is thought to be mediated by nicotinic acetylcholine receptor (nAChR) and probably by muscarinic (m) AChR, since the neuronally evoked CA release from rat adrenal medullae was blocked by both nAChR and mAChR antagonists [29; but see 28]. Our results indicate that the mAChR-mediated CA release from guinea pig chromaffin cells was due to the activation of a nonselective cation (NS) channel [12] and the subsequent stimulation of voltage-dependent Ca 2+ channels [16] and the mAChR was coupled with a NS channel via a pertussis toxin-sensitive GTP (G) binding protein [12]. We recently found the same NS channel to be also involved in hypoxia-induced CA secretion [17].…”

“…In rat CA3 pyramidal cells, slow excitatory postsynaptic potentials (EPSP) mediated by metabotropic glutamate receptors (mGluR) were elicited by trains of 3-10 stimuli at 100 Hz [10], and mGluR1 and mGluR5 were found to be concentrated in a perisynaptic annulus around synaptic junctions using immunogold methods [24]. The stimulation of m4 receptors in guinea-pig [12] and rat [4] adrenal chromaffin cells induced a sustained activation of NS channels during the stimulation. Thus, slow EPSPs due to the activation of NS channels are possibly evoked by a high frequency stimulation of cholinergic fibres in the adrenal medulla.…”

“…mAChR stimulation is thought to activate the NS channel through phosphorylation and an increase in [Ca 2+ ]i is not a prerequisite for the activation [12,15]. NS channels are thus likely to be present close to the mAChR.…”