Concentrations Of Carbamylcholine Research Articles

Action of cholecystokinin and cholinergic agents on calcium transport in isolated pancreatic acinar cells.

COOH-terminal octapeptide of cholecystokinin (CCK-octapeptide) and the cholinergic agent carbamylcholine each produced a fourfold stimulation of calcium outflux in guinea pig isolated pancreatic acinar cells. Neither agent altered calcium influx. Stimulation of calcium outflux was rapid and specific, was abolished by reducing the incubation temperature to 4 degrees C, and was a saturable function of the secretagogue concentration. The concentrations of CCK-octapeptide and carbamylcholine that produced half-maximal stimulation of calcium outflux were 3.1 x 10(-10) M and 4.9 x 10(-5) M, respectively. The cholinergic antagonist antropine competitively inhibited carbamylcholine stimulation of calcium outflux but did not alter stimulation produced by CCK-octapeptide. Stimulation of calcium outflux by maximal concentrations of carbamycholine plus CCK-octapeptide was the same as that produced by a maximal concentration of either agent alone.Calcium outflux became refractory to stimulation by secretagogues, and incubation with either CCK-ostapeptide or carbamylcholine produced a refractoriness to both agents. The relative potencies with CCK and its related fragments stimulated calcium outflux were CCK-octapeptide greater than heptapeptide greater than CCK greater than hexapeptide = gastrin. Secretin, glucagon, and vasoactive intestinal peptide, at concentrations as high as 10(-5) M, failed to alter calcium outflux and did not affect stimulation by CCK-octapeptide or by carbamycholine.

Incorporation of eel electroplax acetylcholinesterase into black lipid membranes. A possible model for the cholinergic receptor

Addition of low concentrations of acetylcholine or carbamylcholine to solutions bathing a black lipid membrane into which electroplax acetylcholinesterase has been incorporated elicits a dramatic increase in the membrane conductance. This change is prevented or reversed by addition of neostigmine or atropine to the system. The magnitude of the conductance increase of the acetylcholinesterase-treated membrane is proportional to the fourth power of the carbamylcholine concentration and, at constant carbamylcholine concentration, to the fourth power of the enzyme concentration in the medium.

Further studies of the effect of calcium on the time course of action of carbamylcholine at the neuromuscular junction.

The rate at which the postjunctional membrane of muscle fibers becomes desensitized to the action of carbamylcholine is increased after the muscle has been soaked in solutions containing increased concentrations of calcium. Some further aspects of this effect of calcium were investigated by measuring changes in the input resistance of single fibers of the frog sartorius during local perfusion of the neuromuscular junction with 2.73 x 10(-3)M carbamylcholine in isolated muscles immersed in 165 mM potassium acetate. It was found that (a) sudden changes in the local concentration of calcium brought about by perfusing fibers with carbamylcholine solutions containing 20 mM calcium, 40 mM oxalate, or 40 mM EDTA were followed within 20 sec by marked changes in the rate of desensitization; (b) prior to 13 sec after the introduction of carbamylcholine, however, no effect on the input resistance could be detected even though the muscle had been presoaked in 10 mM calcium; (c) the ability of high concentrations of calcium to bring about rapid desensitization disappears when a lower concentration of carbamylcholine (0.137 x 10(-3)M) is applied to the muscle fiber. These findings suggest that calcium present in the extracellular fluid can act directly on the postjunctional membrane to promote the desensitization process and that an increased permeability of the membrane to calcium brought about by the presence of carbamylcholine is a factor which contributes to this action.

Factors in the inactivation of postjunctional membrane receptors of frog skeletal muscle.

Several factors which influence the rate of inactivation of muscle postjunctional membrane (PJM) receptors during the sustained application of carbamylcholine (CARB) have been studied by two methods. The rate of inactivation was increased by elevating the tonicity of the bathing medium, by increasing the CARB concentration, by raising the calcium ion concentration, and by substituting SO(4) (=) for Cl(-) ions in the extracellular fluid. The relative effectiveness of calcium and other divalent cations in receptor inactivation was compared. In the absence of calcium, other divalent cations such as magnesium, strontium, or manganese were not efficient substitutes for calcium. In the presence of calcium, the addition of strontium or manganese ions accelerated the rate of receptor inactivation, but the addition of magnesium (up to 12 mM) inhibited this process. The inactivation of the membrane receptors in denervated muscle fibers was found to be similar to that in innervated muscle fibers. Various factors in PJM receptor inactivation are discussed. It is suggested that PJM receptor inactivation is influenced by the binding of calcium ions to sites on the internal surface of the PJM.

Effects of blocking sulfhydryl groups and of reducing disulfide bonds on the acetylcholine-activated permeability system of the electroplax.

Abstract The depolarization of the single-cell preparation of the electroplax of Elecrophorus electricus by acetylcholine, carbamylcholine, and trimethylbutylammonium ion is inhibited by prior treatment of the electroplax with p- chloromercuribenzoate (PCMB) or with 1,4-dithiothreitol (DTT). The inhibition by either agent is characterized by an increase in the concentration of carbamylcholine eliciting a half-maximal response with no great change in the maximum response. The inhibition due to PCMB is reversed by subsequent treatment with thiol compounds, and that due to DTT is reversed by oxidizing agents and by cysteine (but not by other thiol compounds). Washing alone has no effect on the inhibition due to either agent. Treatment of the electroplax with N- ethylmaleimide (NEM) after DTT blocks the reversal of the inhibition by oxidizing agents and by cysteine, added subsequently. NEM alone under the same conditions has no direct effect on the depolarization. It is concluded that PCMB is reacting with sulfhydryl groups and DTT with disulfide bonds, present in one or more component of the acetylcholine-activated permeability system at the junctional regions of the innervated membrane of the electroplax. The evidence is taken as support for the view that some of the components of this system are proteins.

The competitive nature of the action of acetylcholine and local anesthetics

Electrical characteristics of a monocellular electroplax preparation were recorded with intracellular electrodes. 1. 1.|Acetylcholine, carbamylcholine and neostigmine, activators of the receptor protein, rapidly and reversibly block electrical activity in low concentrations with simultaneous depolarization. Tetracaine, physostigmine, the tertiary analogue of neostigmine and curare, inhibitors of the receptor protein, block electrical activity without depolarizing the membrane. 2. 2.|The cell depolarized by acetylcholine is repolarized by curare even in the presence of acetylcholine. Both compounds act primarily on the synaptic membrane. The response to direct stimulation, as postulated by theory, is restored by curare even in the presence of acetylcholine. 3. 3.|In low concentration, 5·10 −5 M, physostigmine, due to its high affinity to cholinesterase, acts as an enzyme inhibitor. In high concentrations, 5·10 −3 M, physostigmine prevents depolarization due to acetylcholine through its action as a receptor inihibitor. 4. 4.|Tetracaine, in 2.5·10 −5 M, reverses the depolarizing action of acetylcholine 2.5·10 −6 M in the presence of the ester and physostigmine. The response to direct stimulation does not return in contrast to curare. 5. 5.|The depolizing action of carbamylcholine in 5·19 −5 M is also overcome by tetracaine 1·10 −4 M. On increasing the concentration of carbamylcholine to 5·10 −4 M the cell was again depolarized. 6. 6.|Puffer fish poison 7·10 −8 M blocks electrical activity by a non-competitive action without depolarization. Even in ten times higher concentration it does not prevent the depolarizing action of acetylcholine in its minumally active concentration.