Effect of Muscarine on Release of Catecholamines From the Perfused Adrenal Gland of the Cat

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

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Inoue

Kuriyama

1991

“…Since the pioneering observations of Dale (1914) and Feldberg, Minz & Tsudimura (1934), the perfused cat adrenal gland has been an excellent model to study the release of catecholamines in response to muscarinic stimulation of its chromaffin cells (Douglas & Poisner, 1965;Lee & Trendelenburg, 1967;Lee, 1972;Kirpekar, Prat & Schiavone, 1982;Borges, Sala & Garcia, 1986;Borges, Ballesta & Garcia, 1987; Ballesta, Borges, Garcia & Hidalgo, 1989; Abad, Garrido, Lopez & Garcia, 1992).…”

Section: Introductionmentioning

confidence: 99%

Ca(2+)‐activated K+ channels modulate muscarinic secretion in cat chromaffin cells.

Uceda

Artalejo

López

et al. 1992

G. UCEDA AND OTHERS Depolarization is probably counteracted by activation of CaFt-dependent K+ channels. Therefore, inhibition of these channels enhances depolarization and firing of action potentials which activate voltage-dependent L-type Ca2+ channels to increase further the CaF+ signal and the secretary response. Thus Ca2+-dependent K+ channels, probably of the small-conductance type (SK), seem to be involved in the modulation of muscarinic-evoked catecholamine release responses in cat adrenal chromaffin cells.

“…Muscarinic stimulation of catecholamine release was first described by Feldberg, Minz & Tsudzimura (1934) in the cat and has since been amply confirmed both in this (Douglas & Poisner, 1965;Lee & Trendelenberg, 1967;Kirpekar, Prat & Schiavone, 1982) and other species, including the gerbil (Douglas, Kanno & Sampson, 1967), rat (Yoshikazi, 1975;Wakade & Wakade, 1983) and guinea-pig (Role & Perlman, 1983). In each of these, however, it has generally been supposed to have a trivial effect by comparison with the nicotinic mechanism.…”

Section: Discussionmentioning

confidence: 99%

Endocrine responses to intra‐aortic infusions of acetylcholine in conscious calves.

Jones

Edwards

Bloom

1991

SUMMARY1. Adrenal responses to intra-aortic infusions of acetylcholine (4 5 nmol min-' kg-' for 10 min) have been investigated in conscious, functionally hypophysectomized, 3-to 6-week-old calves, in the presence and absence of exogenous ACTH (2 ng min-' kg-, i.v.).2. Acetylcholine produced a substantial fall in adrenal vascular resistance, which was significantly reduced in the presence of exogenous ACTH, while producing minimal changes in aortic blood pressure and heart rate.3. There was also a significant rise in right adrenal cortisol output which was sufficient to produce a measurable rise in plasma cortisol concentration. The effect could be accounted for by the increase in adrenal ACTH presentation. It was abolished by pre-treatment with atropine (0-2 mg kg-'). A small but significant rise in aldosterone output during acetylcholine infusions was also abolished in the presence of ACTH.4. Both adrenaline and noradrenaline were released during intra-aortic acetylcholine infusions and these responses were substantially reduced, but not abolished, by pre-treatment with atropine.5. Acetylcholine also stimulated the release of corticotrophin-releasing factor (CRF) and [Met5]enkephalins from the gland. The output of CRF was enhanced and that of free [Met5]enkephalin was significantly reduced in the presence of exogenous ACTH. All these responses were largely, but not completely, suppressed by atropine.6. Acetylcholine also promoted the release of the pancreatic hormones glucagon, insulin and pancreatic polypeptide (PP). The amounts of pancreatic glucagon and insulin that were released were highly dependent on the concentration of glucose in the circulating plasma and all these responses were abolished by atropine.7. It is concluded that acetylcholine is capable of stimulating the release of a wide variety of agonists from the adrenal gland when infused intra-aortically at a dose of 4.5 nmol min-' kg-'. The increase in cortisol output appears to be secondary to an 16 PHY 439 C. T. JONES, A. V. EDWARDS AND S. R. BLOOM increase in blood flow whereas the adrenal medullary responses are not, and appear to be due largely, but not entirely, to activation of muscarinic receptors.