Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Wide-tipped, low-resistance (approximately 1 M omega) pipettes were used to record the whole-cell Cl- current activated by cAMP-dependent protein kinase (PKA) in guinea-pig ventricular myocytes internally dialysed with or without GTP. Without GTP in the pipette, the response to 1 microM-isoprenaline declined with time and eventually disappeared, usually within approximately 20 min of rupturing the membrane and beginning cell dialysis. 2. This rundown of the isoprenaline response occurred more quickly with wider, lower-resistance pipette tips. 3. After complete rundown of the isoprenaline response, histamine (10 microM), another agonist known to elicit the Cl- current, also had no effect, but extracellular forskolin (1 microM) or intrapipette cAMP (1 mM) could still readily elicit the Cl- current. 4. In contrast, with 100 microM-GTP in the pipette, the response to 1 microM-isoprenaline was well maintained for periods greater than 20 min. But, if GTP was then withdrawn from the pipette, a rundown of the isoprenaline response was seen comparable to that in the experiments begun with GTP-free pipette solution. Moreover, in experiments begun without pipette GTP, the addition of 100 microM-GTP to the pipette solution, after the response to isoprenaline had disappeared, was able to restore that Cl- current response. 5. With GTP in the pipette, the forskolin-induced Cl- current could be suppressed by concurrent exposure to carbachol (10 microM). That inhibition was not seen in myocytes pretreated with pertussis toxin. In untreated myocytes dialysed with GTP-free pipette solution, after disappearance of the isoprenaline response, the muscarinic receptor-mediated inhibition was itself abolished. 6. We confirm that both beta-adrenoceptor-mediated activation of the Cl- current by isoprenaline, and muscarinic receptor-mediated inhibition of the forskolin-induced Cl- current, are mediated by G proteins, and conclude that the disappearance of both receptor-mediated responses during whole-cell recording with GTP-free pipette solution reflects the fall of cellular [GTP] below the level required to maintain G protein-dependent signal transduction.
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PMID:Pipette GTP is essential for receptor-mediated regulation of Cl- current in dialysed myocytes from guinea-pig ventricle. 133 50

We investigated regulation of the cardiac L-type calcium channel by intracellular ATP and by alpha 1-adrenergic agonism using single adult guinea pig ventricular cells and the whole-cell patch clamp method. Inclusion of 5 mM ATP in the patch clamp pipette prevented calcium current rundown but did not increase the maximal magnitude of the slow inward calcium current (ICa). During beta 1-adrenergic blockade with 10 microM (-)-propranolol, cells preincubated with 1 microgram/ml pertussis toxin for 2-5 h exhibited a rapid twofold increase in ICa after rupture of the membrane patch when 5 mM ATP was present in the patch clamp pipette. In the absence of ATP, the increase in ICa did not occur. In pertussis toxin-treated cells, 100 microM (-)-phenylephrine inhibited the augmentation of ICa. This inhibitory effect was blocked by 100 nM terazosin, a selective alpha 1-antagonist. The inhibitory effect of alpha 1-adrenergic agonism was not mediated by cAMP-dependent phosphodiesterase since incubation with 100 microM (-)-phenylephrine did not augment the activity of this enzyme. We conclude that regulation of the L-type calcium channel in cardiac cells is complex, and is dependent on a pertussis toxin-sensitive substrate, ATP, and an alpha 1-adrenergic receptor. The marked increase in ICa after pertussis toxin treatment in the presence of ATP indicates significant inhibition of ICa by a pertussis toxin substrate, presumably the guanine nucleotide inhibitory protein (Gi) in the basal state. The inhibitory action of (-)-phenylephrine in pertussis toxin-treated cells is consistent with modulation of ICa by an alpha 1-adrenergic receptor not coupled to Gi.
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PMID:Complex regulation of calcium current in cardiac cells. Dependence on a pertussis toxin-sensitive substrate, adenosine triphosphate, and an alpha 1-adrenoceptor. 196 10

The hypothalamic peptide somatostatin (SRIF) suppresses secretory activity in phenotypically distinct pituitary endocrine cells. We have used tight-seal whole-cell recording techniques to study the peptide's effects on the electrical properties of tumor pituitary cells derived from rat (GH3/B6) and human adenomas that secrete human PRL in a SRIF-sensitive manner. Both cell types exhibited qualitatively similar electrophysiological properties and electrical responses to SRIF. Under the experimental conditions employed the majority of cells spontaneously generated Ca2+-dependent actions potentials. The actions of the peptide on cellular excitability were markedly affected by the presence of horse and fetal calf sera. Without these additives the electrical responses faded and could not be studied in detail. Therefore, recordings were conducted in media containing sera. In the presence of sera almost all cells spontaneously generated Ca2+ action potentials, and peptide-induced changes in excitability were well preserved. SRIF depressed spontaneous and evoked action potential activity in a dose-dependent manner at concentrations that reduced intracellular free calcium ([Ca2+]i) and suppressed basal PRL release. Current and voltage clamp experiments revealed coordinate actions of the peptide on excitable membrane properties. SRIF (1 nM) enhanced a depolarization-activated, rapidly inactivating outward K+ current, thereby effectively reducing the rate at which action potentials occurred. Over the 10-1000 nM range SRIF slowly activated a virtually noninactivating K+ conductance over a wide range of membrane potential. This effectively hyperpolarized cells away from the threshold for triggering Ca2+-dependent action potentials and shunted the membrane. The peptide induced K+ conductance activated at the level of the resting potential was progressively lost during the intracellular dialysis of whole-cell recording. Dilute aqueous lysates of cells included in the patch pipette prevented much of the rundown of this SRIF-induced electrical response while inclusion of an ATP-regenerating system preserved some of the peptide action. Over the 10-100 nM concentration range SRIF also reduced voltage-dependent Ca2+ current. Furthermore, pretreatment of cells with pertussis toxin abolished SRIF action on cellular excitability, suggesting that SRIF can regulate the function of ionic channels through GTP-binding proteins (G proteins). The results demonstrate that SRIF acts coordinately on the primary conductances expressed in tumor PRL cells to attenuate or block Ca2+ action potential generation and thus Ga2+ entry from extracellular sources.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Somatostatin blocks Ca2+ action potential activity in prolactin-secreting pituitary tumor cells through coordinate actions on K+ and Ca2+ conductances. 245 3

The Ca2+ current recorded by the whole-cell technique in chromaffin cells shows, before the often described rundown, a transient facilitation or runup. Initial current amplitude was 570 +/- 165 pA and then it increased by 49 +/- 23% (n = 19, SD) over 2 +/- 1 min in the absence of adenosine 5'-triphosphate (ATP). In the presence of ATP, this process occurred with the same magnitude but it was slowed in a dose-dependent manner, lasting 17 +/- 2 min with 2 mM ATP (n = 8). Since adenosine 5'-diphosphate (ADP) does not reproduce this ATP effect, a complex series of phosphorylations is likely to intervene and we show that, at least, a cAMP-dependent i.e., cyclic adenosine monophosphate) phosphorylation occurs. Pertussis toxin (PTX) pretreatment yielded an already maximal Ca2+ current (around 1000 pA) at the time of the patch rupture, which only slightly increased thereafter (10%, n = 11). Also, guanosine 5'-diphosphate (GDP) and guanosine 5'-O-(2-thiodiphosphate) (GDP[ beta s]), induced a fast runup, which was absent in the presence of GTP. Furthermore, we show that facilitation does not occur in the presence of dihydrophyridine (DHP) antagonists. Globally, our data suggest that an ATP-dependent phosphorylation stabilizes the inhibitory control exerted by a PTX-sensitive G protein and, as a result, slows down the facilitation of L-type Ca2+ channels. The recruitment of L-type channels can also be facilitated by the application of a DHP agonist or a depolarizing prepulse protocol.l We show that these processes are only effective over a period which parallels the runup and are not additive to it.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:ATP and G proteins affect the runup of the Ca2+ current in bovine chromaffin cells. 749 Dec 66

Activity of high-threshold voltage activated neuronal Ca2+ channels, including dihydropyridine-sensitive (L-type) channels, rapidly disappears during cell dialysis in whole-cell recording conditions or after excision of a patch. To date, this phenomenom has been mainly related to phosphatase or protease activity. On the other hand, it has been suggested that Ca2+ channels may be regulated by G-proteins. Therefore, disruption of this regulatory pathway may also be involved directly or indirectly in the rundown process. Here, we show that treatment of cultured cerebellar granule cells with pertussis toxin (PTX) increases to 70% the probability for excising patches that display L-type Ca2+ channels activity in the inside-out recording configuration. Quantitative study indicates that, except a half decrease in the open probability, most features of the channel activity are retained after patch excision with minor modifications. The characteristics of the channel activity did not change with time during at least the first 9 min of the inside-out configuration. In addition, comparison of unitary currents recorded in the cell-attached, configuration on treated and nontreated cells demonstrates that the PTX treatment slows the activation kinetics of the current and increases the duration of channel openings evoked at -20 mV but not at 0 mV depolarizing potential. These data suggest that L-type Ca2+ channel activity are under a tonic regulation of a PTX-sensitive mechanism, which is implied in the run-down process.
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PMID:Maintained L-type Ca2+ channel activity in excised patches of PTX-treated granule cells of the cerebellum. 766 85

We studied, in rat sensory neurons, the modulation of high voltage-activated Ca2+ currents (ICa) mediated by the pertussis toxin-sensitive activation of muscarinic receptors, which were found to be of subtypes M2 or M4. Muscarine reversibly blocked somatic Ca2+ spikes but strong predepolarizations only partially relieved the inhibited Ca2+ current. On the other hand, the putative coupling messenger could not rapidly diffuse towards channels whose activity was recorded from a macro-patch. The perforated patch technique virtually prevented the response rundown present during whole-cell experiments. Both omega-conotoxin GVIA (omega-CgTx)-sensitive channels and omega-CgTx- and dihydropyridine-resistant channels are coupled to the muscarinic receptor, but not the L-channel. When measured in the same neuron, dose-response relationships for the first and subsequent agonist applications differed; maximal inhibition, the reciprocal of half-maximal concentration and the Hill coefficient were always highest in the first trial. Muscarine and oxotremorine exhibited monotone dose-response curves, but oxotremorine-M showed non-linear relationships which became monotonic when cells were intracellularly perfused with inhibitors of protein kinase A (PKA) and C (PKC), suggesting that either PKA or receptor-induced PKC could phosphorylate and thus inactive G-proteins or other unknown proteins involved in inhibitory muscarinic actions on ICa. In summary, these data provide a preliminary pharmacological characterization of the muscarinic inhibition of the Ca2+ channels in sensory neurons, with implications about agonist specificity and the interplay between signalling pathways.
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PMID:Muscarinic regulation of Ca2+ currents in rat sensory neurons: channel and receptor types, dose-response relationships and cross-talk pathways. 801 75

1. Although peptides are important modulators of synapses, their action on synapse-glia interactions remain unclear. The amphibian neuromuscular junction (NMJ) was used to examine the effects of substance P (SP) on perisynaptic Schwann cells (PSCs), glial cells at the frog NMJ, by monitoring changes in intracellular Ca2+. 2. SP induced Ca2+ responses that were mimicked by the neurokinin 1 receptor (NK-1) agonist septide and with a shorter delay by the SP fragment, SP(6-11). SP and SP(6-11) responses were blocked by NK-1 antagonists SR140333 and LY303870. 3. Ca2+ responses remained unchanged when extracellular Ca2+ was removed but were blocked after pertussis toxin (PTX) treatment, indicating that the receptors were linked to internal stores of Ca2+ via a PTX-sensitive G-protein. 4. The slowly hydrolysable NK-1 agonist [Sar9, Met(O2)11]-SP only induced Ca2+ responses when applied for a long period of time and not during brief, local applications, suggesting the involvement of SP hydrolysis. Acetylcholinesterase (AChE) may not be involved in SP degradation since Ca2+ responses evoked by SP were unchanged in the presence of the cholinesterase inhibitor neostigmine. 5. Ca2+ responses induced by muscarine and nerve stimulations were almost abolished when preceded by SP applications, while those induced by ATP were significantly reduced. The rundown of the nerve-evoked Ca2+ responses in PSCs was attenuated in the presence of SR140333. 6. These results indicate that endogenous SP is involved in the regulation of PSC activity and that SP is an important modulator of glial cell Ca2+ signalling and synapse-glia communication.
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PMID:Endogenous peptidergic modulation of perisynaptic Schwann cells at the frog neuromuscular junction. 972 29

The modulation of L-type Ca2+ currents (I(Ca,L)) by the basal activities of G proteins was studied in adult guinea pig ventricular myocytes by whole-cell patch-clamp techniques. With intrapipette guanosine triphosphate (GTP) (100 microM), a specific inhibition of G1 proteins by pertussis toxin (PTX) produced an increase in the basal density of I(Ca,L) (from 11.0+/-0.8, n = 13, to 25.0+/-2.0 pA/pF, n = 11, at OmV test potential). In addition, PTX shifted the forskolin (Fsk) concentration-I(Ca,L) response relation significantly leftward (EC50, = 63.7+/-12.5 vs 625+/-75 nM). With intrapipette guanosine diphosphate (GDP)betaS (1 mM), the Fsk-I(Ca,L) relation was also shifted leftward (EC50 = 197+/-18.3 vs 781+/-82.5 nM). However, chronic GDPbetaS dialysis accelerated the rundown of I(Ca,L) significantly, suggesting a potential contribution of Gs proteins in maintaining basal I(Ca,L). In contrast, intra-pipette GTPgammaS (100 microM) produced a transient rise in I(Ca,L) from 11.0+/-3.0 to 22.8+/-7.0 pA/pF (in 3.4 min after whole-cell formation at 0 mV, n = 9), presumably through the activation of Gs proteins. It was followed by a gradual decline in I(Ca,L) (to 15.5+/-3.5 pA/pF), which was still enhanced by Fsk (EC50 = 1450+/-98 nM), indicating that the current decay was not solely due to rundown but to activation of Gi proteins. Gs, in addition to Gi proteins, show sufficient basal activity to modulate I(Ca,L) in an agonist-independent manner.
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PMID:Agonist-independent modulation of L-type Ca currents by basal Gs protein activities in single guinea pig ventricular myocytes. 1156 Mar 60

The present study investigated the membrane mechanisms underlying the inhibitory influence of melatonin on suprachiasmatic nucleus (SCN) neurones in a hypothalamic slice preparation. Perforated-patch recordings were performed to prevent the rapid rundown of spontaneous firing rate as observed during whole cell recordings and to preserve circadian rhythmicity in SCN neurones. In current-clamp mode melatonin (1 microM or 1 nM) application, in the presence of agents that block action potential generation and fast synaptic transmission, resulted in a membrane hyperpolarisation accompanied with a decrease in input resistance in the majority of SCN neurones (71-86%). The amplitude of the hyperpolarisation was not found to be significantly different between circadian time 5-12 and 14-21. In voltage-clamp mode melatonin (1 microM or 1 nM) induced an outward current accompanied with an increase in membrane conductance. The current was found to be mainly potassium driven with voltage kinetics resembling those of an open rectifying potassium conductance. Investigations into the signal transduction mechanism revealed melatonin-induced inhibition of SCN neurones to be sensitive to pertussis toxin but independent of intracellular cAMP levels and phospholipase C activity. The present study shows that melatonin, at night-time physiological concentrations, reduces the neuronal excitability of the majority of SCN neurones independent of the time of application in the circadian cycle. Thus in vivo melatonin may be important for circadian time-keeping by amplifying the circadian rhythm in SCN neurones, by lowering their sensitivity to phase-shifting stimuli occurring at night.
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PMID:Melatonin generates an outward potassium current in rat suprachiasmatic nucleus neurones in vitro independent of their circadian rhythm. 1174 50

Stimulation of muscarinic acetylcholine receptors (mAChRs) can activate an inward rectifier K(+) current (I(KACh)), which is mediated by the M(2) subtype of mAChR in cardiac myocytes. Recently, a novel delayed rectifier-like K(+) current mediated by activation of the cardiac M(3) receptors (designated I(KM3)) was identified, which is distinct from I(KACh) and other known K(+) currents. While I(KACh) is known to be a G(i) protein-gated K(+) channel, the signal transduction mechanisms for I(KM3) activation remained unexplored. We studied I(KM3) with whole-cell patch clamp and macropatch clamp techniques. Whole cell I(KM3) activated by choline persisted with minimal rundown over 2 h in presence of internal GTP. When GTP was replaced by guanyl-5'-yl thiophosphate, I(KM3) demonstrated rapid and extensive rundown. While I(KACh) (induced by ACh) was markedly reduced in cells pretreated with pertussis toxin, I(KM3) was unaltered. Intracellular application of antibodies targeting alpha-subunit of G(i/o) protein suppressed I(KACh) without affecting I(KM3). Antibodies targeting the N and the C terminus, respectively, of G(q) protein alpha-subunit substantially depressed I(KM3) but failed to alter I(KACh). The antibody against beta-subunits of G proteins inhibited both I(KACh) and I(KM3). I(KM3) activated by choline in the cell-attached mode of macropatches persisted in the cell-free configuration. Application of purified G(q) protein alpha-subunit or betagamma-subunit of G proteins or guanosine 5'-O-(thiotriphosphate) to the internal solution activated I(KM3)-like currents in inside-out patches. Our findings revealed a novel aspect of receptor-channel signal transduction mechanisms, and I(KM3) represents the first G(q) protein-coupled K(+) channel. We propose that the G protein-coupled K(+) channel family could be divided into two subfamilies: G(i) protein-coupled K(+) channel subfamily and G(q) protein-coupled K(+) channel subfamily.
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PMID:The M3 receptor-mediated K(+) current (IKM3), a G(q) protein-coupled K(+) channel. 1514 Aug 74


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