Short-term Desensitization Research Articles

P-34 - The mechanism of development of short-term desensitization in isolated smooth muscle cells showing an all-or-none response to acetylcholine

P-34 - The mechanism of development of short-term desensitization in isolated smooth muscle cells showing an all-or-none response to acetylcholine

O-50 - Regulation of signal transduction and intracellular Ca stores in guinea pig taenia caecum: Short-term desensitization of muscarinic cholinergic receptors and histamine H1 receptors

O-50 - Regulation of signal transduction and intracellular Ca stores in guinea pig taenia caecum: Short-term desensitization of muscarinic cholinergic receptors and histamine H1 receptors

Effect of Ca 2+ deprivation on short-term desensitization of isolated smooth muscle cells showing an all-or-none response to acetylcholine

1. 1. Short-term desensitization of the contractile response of isolated smooth muscle cells from guinea pig taenia caecum to acetylcholine was examined in the absence of external Ca 2+. 2. 2. Isolated smooth muscle cells contracted to 10 −7−10 −6 M acetylcholine, showing an all-or-none response. 3. 3. Desensitization was induced by incubating the cells with 10 −4 M acetylcholine for 10 min in Ca 2+-free solution. 4. 4. Desensitized cells showed an all-or-none response but required a higher concentration of acetylcholine for induction of contraction, indicating that the desensitization was due to a change in the threshold concentration. 5. 5. Desensitization is suggested to be induced before massive influx of Ca 2+ into the cells.

Effects of local anaesthetics on short-term desensitization of guinea-pig taenia caecum to histamine.

1 Short-term desensitization to histamine was induced by incubating guinea-pig taenia caecum with 10(-4)M histamine for 30 min (desensitizing incubation) in normal Locke-Ringer solution or Ca-free Locke-Ringer solution containing 0.2 mM EGTA. This desensitization was measured as a reduction of the maximal contractile response. 2 The effects of the presence of local anaesthetics during the desensitizing incubation were examined. Results showed that tetracaine, procaine, procainamide, oxybuprocaine and lignocaine inhibited the desensitization, whereas dibucaine, benzocaine and mepivacaine did not. 3 The inhibitory effects of these drugs on the desensitization were not correlated with their lipid solubility nor with the potency of their known effects, such as membrane stabilization, Ca channel blockade, calmodulin antagonism, or inhibition of C-kinase. 4 It is concluded that the inhibitory effects of local anaesthetics on the desensitization are not due to their non-specific membrane-stabilizing effects per se, but to some other action.

Short-term desensitization of muscarinic K+ channel current in isolated atrial myocytes and possible role of GTP-binding proteins

The short-term desensitization of the acetylcholine (ACh)-induced K+ channel current was examined in single atrial cells of guinea-pig heart. The tight-seal whole cell voltage clamp technique was used. The solution in the pipettes contained GTP or guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma S, a non-hydrolyzable GTP analogue). In GTP-loaded cells, ACh evoked a specific K+ channel current via GTP-binding proteins (G) in a dose-dependent manner. The K+ current showed agonist-dependent desensitization similar to those reported in other cardiac tissues (Nilius 1983; Carmeliet and Mubagwa 1986). The cellular response to ACh was also desensitized by activation of P1-purinergic receptors with adenosine (Ado). In GTP-gamma S-loaded cells, the K+ current was gradually induced even in the absence of agonists, probably due to direct activation of G proteins by GTP-gamma S. In the early phase of the spontaneous current increase, ACh evoked a large current transiently. As the GTP-gamma S-induced activation of the current progressed, the magnitude of the ACh-evoked current transient became smaller and finally negligible. Similar results were obtained when Ado was used as an agonist instead of ACh to induce the K+ current. Therefore, it is indicated that the agonist-receptor interaction may not be essential for the desensitization of ACh-induced K+ current in atrial myocytes.

Short-term cholinergic desensitization of rat pancreatic secretory response

Dispersed pancreatic acini were first exposed to carbamylcholine (10(-7)-10(-4) M) for 60 min, washed, and reexposed to this same agonist (10(-8)-10(-3) M) for 15 min. During this second incubation, the functional secretory capacity of these acini was evaluated by measuring amylase release. Acini preexposed to concentrations of carbamylcholine of 10(-6) M or greater showed shifts to the right in the subsequent carbamylcholine dose-response curves of amylase release. A 3-h recovery period (without carbamylcholine) did not restore the altered carbamylcholine dose-response curve. Ca2+ concentrations of 10(-7) M or 2.5 X 10(-3) M instead of 0.5 X 10(-3) M during the 60-min preincubation did not affect the desensitization process. With use of N-[3H]methylscopolamine to evaluate muscarinic receptors, the only changes observed after desensitization were a significant decrease in the high-affinity and an equivalent increase in that of the low-affinity receptors. After cholinergic exposure amylase release stimulated by caerulein was only slightly modified, whereas amylase release in response to a phorbol ester 12-O-tetradecanoylphorbol-13-acetate and to the ionophore A23187 was not altered. These data indicate that short-term desensitization with a cholinergic agent is relatively specific to muscarinic agonists, causes changes in the muscarinic receptor high- and low-affinity concentration but does not alter intracellular steps after calcium mobilization or protein kinase C activation known to be involved in the secretion process.

Desensitization of isolated smooth muscle cells from guinea pig taenia caecum to acetylcholine.

The role of tissue organization of smooth muscle in short-term desensitization to acetylcholine (ACh) was examined by studying the desensitization of isolated single cells from guinea pig taenia caecum. Cells were isolated by collagenase digestion. The conditions during cell isolation were adjusted to obtain cells that showed repeated contractions. The cells contracted on treatment with 10(-7)-10(-6) M ACh, showing an all-or-none response. Desensitized cells also showed an all-or-none response but required a higher concentration of ACh for induction of contraction; i.e., the magnitude of their maximal response was not changed appreciably but the threshold concentration of ACh for their contraction was raised. Incubation of the whole tissue with 10(-4) M ACh for 10 min also caused desensitization. This desensitization was accompanied by reduction of the contractile response at intermediate concentrations. The mode of desensitization of isolated cells determined from the average response of the isolated cells was almost the same as that of whole muscle. It is concluded that the desensitization occurred in each cell irrespective of its tissue organization and that the desensitization was due to an increase of the threshold for contraction to ACh of each cell.

On the molecualr mechanisms of the activation of K+ channels by acetylcholine in cardiac cell membrane.

Recent progresses in the understandings of molecular mechanisms underlying activation of K+ channels by acetylcholine (ACh) were reviewed. Electrophysiological studies using patch clamp techniques revealed that GTP-binding proteins, whose functions are inhibited by pertussis toxin, couple m-ACh and adenosine receptors to a K+ channel in the cardiac cell membrane. The activation of G proteins by intracellular GTP analogues has an absolute requirement for intracellular Mg2+. During activation with GTP and Mg2+, G proteins may be dissociated into its subunits (α-GTP, βγ). Reoonstitutional experiments using purified subunits from bovine brain showed that βγ subunits can activate the K+ channel. A simple model for activation of the channel by G proteins has been proposed.Recently, it was shown that G proteins may also be involved in the short-term desensitization of the ACh-induced K+ channel current. The precise mechanisms of the desensitization is now awaited to be clarified.

Capsaicin-induced changes in behavioural thermoregulation of newborn rabbits ( Lepus cuniculus)

1. 1.|An injection of capsaicin into normal young rabbits resulted in a preference for a cooler environment, signs of increased heat loss, and a suppression of the overall metabolic rate. 2. 2.|Body temperature declines with the preferred temperature, despite brown fat activation. 3. 3.|The response is greatly reduced after short-term desensitization, although the spontaneous motility, temperature selecting behaviour and body temperature appear to be normal.

Alterations in Muscarinic Receptors of Ventricular Muscle in Carbachol-Induced Short-Term Desensitization

The inhibitory action of a muscarinic agonist on the contractile response of cardiac muscle is transient due to short-term desensitization of muscarinic cholinergic receptors. Studies were made on the binding of the muscarinic antagonist L-[3H]-qutnuclidinyl benzilate ([3H]QNB) to the muscarinic receptor in the membrane fraction of ventricular muscle of guinea pigs desensitized by perfusion with carbachol for 10 min. Desensitization did not change the maximum binding or equibilium dissociation constant (Kd) of [3H]QNB, but shifted the inhibition curves of [3H]ONB binding by carbachol to the right both in the presence and absence of 5 -guanylyl imidodiphosphate (GppNHp). Analysis of these inhibition curves with a multiple site model suggested that superhigh and high affinity agonist binding sites were convened to low affinity sites in the desensitized state. GppNHp has additive effects to the prior exposure to carbachol, suggesting a different site of action from shon-term exposure of agonist. We conclude that agonist-induced shon-term desensitization of the muscarinic receptor of ventricular muscle is caused by reduction in the affinity of the receptor for agonist without reduction in its amount or affinity for antagonist.

P2B0306) - Membrane-stabilizing drugs inhibiting short-term desensitization induced by histamine in guinea-pig taenia caecum.

P2B0306) - Membrane-stabilizing drugs inhibiting short-term desensitization induced by histamine in guinea-pig taenia caecum.

Effects of Quin-2, an intracellular Ca chelator, and TMB-8, an intracellular Ca antagonist, on the short-term desensitization to histamine in guinea pig taenia caecum

1. 1.|The effects of Quin-2-acetoxylmethylester, an intracellular Ca ion chelator, and 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate-HCl (TMB-8), an intracellular Ca antagonist, on short-term desensitization to histamine were tested in guinea pig taenia caecum. 2. 2.|Desensitization was induced by incubating the muscle with 10 −4 M histamine for 30 min and the recovery from the desensitization needed ca. 90 min. 3. 3.|Both Quin-2-acetoxylmethylester (50 μM for 120 min) and TMB-8 (5 μM for 20 min) suppressed the desensitization. 4. 4.|Modes of action and structures of both agents are quite different but both may reduce the availability of intracellular Ca ion. It is possible that reduction of intracellular Ca ion suppressed the desensitization.

P-68) - Effects of Ca++ on short-term desensitization induced by histamine in guinea-pig taenia caecum

P-68) - Effects of Ca++ on short-term desensitization induced by histamine in guinea-pig taenia caecum

The brainstem auditory evoked response (baer) in patients with acoustic neuromas

Escape is among the simplest animal behaviors employed to study the neural mechanisms underlying learning. Teleost fishes exhibit behavioral learning of fast escape initiated with a C-shaped body bend (C-start). C-starts are subdivided into short-latency (SLC) and long-latency (LLC) types in larval zebrafish. Whether these two can be separately modified, and the neural correlates of this modification, however, remains undetermined. We thus performed Ca2+ imaging of Mauthner (M-) cells, a pair of giant hindbrain neurons constituting a core element of SLC circuit, during behavioral learning in larval zebrafish. The Ca2+ response corresponding to a single spiking of the M-cells was coupled with SLCs but not LLCs. Conditioning with a repeated weak sound at subthreshold intensity to elicit C-starts selectively suppressed SLC occurrence for 10 min without affecting LLC responsiveness. The short-term desensitization of SLC was associated with the suppression of M-cell activity, suggesting that changes in single neuron responsiveness mediate behavioral learning. The conditioning did not affect the acoustically evoked mechanotransduction of inner ear hair cells, further suggesting plastic change in transmission efficacy within the auditory input circuit between the hair cells and the M-cell.

Desensitization to histamine in the absence of external Ca++ in the guinea-pig taenia caecum.

Short-term desensitization of the contractile response of the guinea-pig taenia caecum to histamine was tested in the absence of Ca++. Desensitization was monitored both by the fall of histamine response and by the decrease of irreversible blockade by phenoxybenzamine. In Ca++-free solution with 0.2 mM EGTA, desensitization occurred as in normal physiological solution containing Ca++.

Desensitization of the alpha adrenergic receptor system in guinea pig vas deferens

Desensitization induced by alpha adrenergic (α-Ad) stimulation was investigated in organ cultured vas deferens of guinea pig. Brief exposure (1–2 min) of the muscle to noradrenaline (NA) caused short-term desensitization to both NA and acetylcholine (ACh), but not to high K +. After removing the agonist this desensitization completely disappeared within 15 min. Prolonged exposure to NA (i.e., cultured with NA for 3–24 hr) elicited longterm desensitization to NA, ACh and K + (50 mM), but it did not change the maximal contraction by high K + (154 mM). After removing NA from the culture medium the response to the agonist was restored to normal within 24 hr, but not within 15 min. The number and affinity of α-Ad and muscarinic ACh receptors, which were measured by the binding of 3H-WB4101 and 3H-QNB, respectively, were not changed in the muscle during these treatments. Moreover, long-term desensitization, but not short-term desensitization, was depressed by the concomitant presence of cycloheximide. The possible mechanisms of desensitization were discussed in comparison with those of various receptor systems.

Opioids regulate cGMP formation in cloned neuroblastoma cells

Opioid agonists caused a rapid dose-related elevation of the cGMP content of N4TG1 murine neuroblastoma cells. An excellent correlation was found between the rank order of potency of agonists in stimulating cGMP accumulation and in displacing [(3)H]etorphine ([(3)H]ETP) bound to intact cells. The narcotic antagonists naloxone and diprenorphine failed to increase cGMP content; moreover, in the presence of 5 muM naloxone, the EC(50) of ETP increased from approximately 9 nM to > 1 muM. N4TG1 cells that had been incubated for 20 min with 0.32 muM ETP and thoroughly washed displayed a marked loss in sensitivity to subsequent ETP challenge. This desensitization was characterized by a 40-50% decrease in maximal response and an increase in the apparent K(a) of ETP from 4 to 50 nM. Desensitization was complete after a 7-min incubation with 0.32 muM ETP (t((1/2)) approximately 1 min) and was only slowly reversible (t((1/2)) > 60 min). Naloxone (5 muM) and diprenorphine (0.1 muM) failed to elicit desensitization, but they blocked ETP-induced desensitization. Dextrophan and (+)-ethylketazocine were <1% as effective as levorphanol and (-)-ethylketazocine, respectively, in both stimulating cGMP accumulation and inducing desensitization. When the binding of [(3)H]ETP (0.2-20 nM) was examined under identical experimental conditions, cells that were completely desensitized by incubation with ETP (7 min with 0.32 muM or 20 min with 15 nM) showed no loss of high-affinity recognition sites. After longer incubation with ETP (0.32 muM for 20-60 min), the maximal binding of [(3)H]ETP was reduced 17-41%. The specific short-term desensitization of cGMP accumulation is not mediated or accompanied by a decrement in the number of agonist binding sites.

Involvement of calcium channels in short-term desensitization of muscarinic receptor-mediated cyclic GMP formation in mouse neuroblastoma cells.

Incubation of mouse neuroblastoma cells (clone N1E-115) with Mn2+ resulted in a rapid and transient increase in cyclic GMP formation. This effect appears to be due to an increase in calcium influx because it did not occur in the absence of extracellular calcium or in the presence of verapamil, a calcium transport inhibitor. In addition, Mn2+ inhibited muscarinic receptor-mediated cyclic GMP responses. The ability of Mn2+ to increase cyclic GMP levels was markedly diminished in cells desensitized to the effects of carbamoylcholine, suggesting that this densensitization involves inactivation of calcium entry.

Long-term regulation of muscarinic acetylcholine receptors on cultured nerve cells

Incubation of mouse neuroblastoma cells (clone 1LE-115) with the muscarinic agonist, carbachol, resulted in a time-dependent desensitization to muscarinic receptor-mediated cyclic GMP formation and a decrease in the number and affinity of muscarinic receptors as measured by the binding to intact cells of the muscarinic antagonist, [ 3H]quinuclidinyl benzilate (QNB). The decrease in responsiveness to cyclic GMP formation reached a maximum after a 15-minute exposure to 1 mM carbachol (short-term desensitization) whereas changes in [ 3H] QNB binding became apparent only after a one hour exposure and reached a maximum after about 12 hrs (long-term desensitization). Recovery of sensitivity after short-term desensitization was rapid, suggesting that this process may involve a conformational change in the muscarinic receptor. In contrast, recovery after long-term desensitization was prolonged and could be slowed by the inhibition of protein synthesis. These results indicate that different cellular mechanisms are involved in the short-term and long-term desensitization of muscarinic receptors.

Effects of reductions in social anxiety on behaviour in

Abstract Male students characterized by anxiety, avoidance and incompetence in heterosexual situations received treatment for heterosexual anxiety by either traditional or short-term desensitization or relaxation training. Only the desensitization subjects reported significant reductions in anxiety and avoidance. Self-appraised improvements in appropriateness of current behaviour and in other-perceived interaction competence for heterosexual situations were reported at posttreatment. These improvements, however, were not accompanied by significant changes in their behaviour as measured by the self-reported frequency of their social activities or participatory forms of social interaction. At follow-up, the desensitization subjects reported significant deteriorations in the appropriateness of their own behaviour even though they still perceived that others would judge their behaviour as competent. The treatment effects of relaxation training were in general, no different to those of no treatment.