Regulation of two ion channels by a common muscarinic receptor-transduction system in a vertebrate neuron

SUMMARY1. Intracellular recordings were obtained from neurones in the guinea-pig superior cervical ganglion (SCG) in vitro to study the electrophysiological effects of endogenously released histamine.2. Guinea-pigs were actively sensitized to the specific antigen, ovalbumin. SCG removed from these animals rapidly released a significant proportion of their endogenous histamine stores into the extracellular space upon exposure to the sensitizing antigen. Several observations indicated that the released histamine was derived from ganglionic mast cells.3. The electrophysiological effects produced by antigen challenge in a neurone mimicked qualitatively and quantitatively those effects produced by exogenously applied histamine in the same neurone. Under current clamp the membrane effects of antigen and histamine included a transient depolarization, an increase in input resistance and transient blockade of a long-duration component of the spike afterhyperpolarization. In voltage clamp histamine and antigen produced an inward current and decreased membrane conductance.4. Histamine H1, but not H2 or H3 receptor antagonists prevented the membrane depolarization to both histamine and antigen treatments.5. These convergent biochemical, physiological and pharmacological data demonstrate that a sufficient quantity of endogenous histamine is released by an antigenic stimulus in SCG from sensitized guinea-pigs to affect specific electrophysiological characteristics of neurones. Histamine may thus be involved in mediating interactions between the mammalian immune system and the peripheral sympathetic nervous system.

Section: Mechanism Of Histamine-mediated Effects On Scg Neuronessupporting

confidence: 66%

Endogenous histamine excites neurones in the guinea‐pig superior cervical ganglion in vitro.

Christian

Undem

Weinreich

1989

“…Addition of 10 /LM-H-7 to the pipette solution did not affect the muscarinic response. In addition, muscarinic activation of the cation channel could not be mimicked by applying ,u.ym-Pb(Bu)2 or 10 jCM-OAG for 3-5 min, a time which was found to be sufficient for inhibition of the M-current in dispersed sympathetic neurones (Tsuji, Minota & Kuba, 1987) or NG 108-15 cells (Brown & Higashida, 1988). However, long treatment with protein kinase C activator seems to modify the muscarinic receptor-cation channel complex through the action of protein kinase C. The long treatment of chromaffin cells with Pb(Bu)2, but not with the inactive phorbol ester, suppressed muscarinic sensitivity.…”

Section: Signal Transduction Mechanismmentioning

confidence: 93%

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

Inoue

Kuriyama

1991

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

“…Protein kinase C (Castagna et al 1982) has been proposed as a second messenger (Tsuji, Minota & Kuba, 1987). It seems unlikely that cyclic AMP mediates the muscarinic actions (see Brown, 1988).…”

Section: Involvement Ofprotein Kinase a In Ih Regulationmentioning

confidence: 99%

Cyclic AMP regulates an inward rectifying sodium‐potassium current in dissociated bull‐frog sympathetic neurones.

Tokimasa

Akasu

1990

115

SUMMARY1. Bull-frog sympathetic neurones in primary culture were voltage clamped in the whole-cell configuration. The pipette solution contained ATP (5 mM).2. A hyperpolarization-activated sodium-potassium current (H-current: IH) was separated from other membrane currents in a nominally calcium-free solution containing cobalt (2 mM), magnesium (4 mM), barium (2 mm), tetraethylammonium (20 mM), tetrodotoxin (3 /,M), apamin (30 nM) and 4-aminopyridine (1 mm). IH was selectively blocked by caesium (10-300 ,UM).3. The steady-state activation Of IH occurred between -60 and -130 mV. The H-conductance was 4-1-6-6 nS at the half-activation voltage of -90 mV. With the concentrations of potassium and sodium ions in the superfusate at 20 and 70 mm, respectively, the reversal potential of IH was about -20 mV. IH was activated with a time constant of 2-8 s at -90 mV and 22 'C. The Q10 between 16 and 26 'C was 4-3. 4. A non-hydrolysable ATP analogue in the pipette solution did not support IH activation. Intracellular 'loading' of GTP-y-S (30-500,M) led to a progressive activation of IH-5. Forskolin (10 ,UM) increased the maximum conductance ofIH by 70 %. This was associated with a depolarizing shift in the half-activation voltage (5-10 mV) and in the voltage dependence of the activation/deactivation time constant ofIH.6. Essentially the same results as with forskolin were obtained by intracellular 'loading' with cyclic AMP (3-10 /LM) or bath application of 8-bromo cyclic AMP (0-1-1 mM), dibutyryl cyclic AMP (1 mM) and 3-isobutyl-1-methylxanthine