scholarly journals cAMP-Dependent Signaling Restores AP Firing in Dormant SA Node Cells via Enhancement of Surface Membrane Currents and Calcium Coupling

2021 ◽  
Vol 12 ◽  
Author(s):  
Kenta Tsutsui ◽  
Maria Cristina Florio ◽  
Annie Yang ◽  
Ashley N. Wirth ◽  
Dongmei Yang ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Firing Rate ◽  
De Novo ◽  
Surface Membrane ◽  
Initial Response ◽  
Functional Coupling ◽  
Membrane Hyperpolarization ◽  
Clock Proteins ◽  
Diastolic Depolarization ◽  
Current Densities

Action potential (AP) firing rate and rhythm of sinoatrial nodal cells (SANC) are controlled by synergy between intracellular rhythmic local Ca2+ releases (LCRs) (“Ca2+ clock”) and sarcolemmal electrogenic mechanisms (“membrane clock”). However, some SANC do not fire APs (dormant SANC). Prior studies have shown that β-adrenoceptor stimulation can restore AP firing in these cells. Here we tested whether this relates to improvement of synchronization of clock coupling. We characterized membrane potential, ion currents, Ca2+ dynamics, and phospholamban (PLB) phosphorylation, regulating Ca2+ pump in enzymatically isolated single guinea pig SANC prior to, during, and following β-adrenoceptor stimulation (isoproterenol) or application of cell-permeant cAMP (CPT-cAMP). Phosphorylation of PLB (Serine 16) was quantified in the same cells following Ca2+ measurement. In dormant SANC LCRs were small and disorganized at baseline, membrane potential was depolarized (−38 ± 1 mV, n = 46), and ICaL, If, and IK densities were smaller vs SANC firing APs. β-adrenoceptor stimulation or application of CPT-cAMP led to de novo spontaneous AP generation in 44 and 46% of dormant SANC, respectively. The initial response was an increase in size, rhythmicity and synchronization of LCRs, paralleled with membrane hyperpolarization and small amplitude APs (rate ∼1 Hz). During the transition to steady-state AP firing, LCR size further increased, while LCR period shortened. LCRs became more synchronized resulting in the growth of an ensemble LCR signal peaked in late diastole, culminating in AP ignition; the rate of diastolic depolarization, AP amplitude, and AP firing rate increased. ICaL, IK, and If amplitudes in dormant SANC increased in response to β-adrenoceptor stimulation. During washout, all changes reversed in order. Total PLB was higher, but the ratio of phosphorylated PLB (Serine 16) to total PLB was lower in dormant SANC. β-adrenoceptor stimulation increased this ratio in AP-firing cells. Thus, transition of dormant SANC to AP firing is linked to the increased functional coupling of membrane and Ca2+ clock proteins. The transition occurs via (i) an increase in cAMP-mediated phosphorylation of PLB accelerating Ca2+ pumping, (ii) increased spatiotemporal LCR synchronization, yielding a larger diastolic LCR ensemble signal resulting in an earlier increase in diastolic INCX; and (iii) increased current densities of If, ICaL, and IK.

scholarly journals Fusicoccin (FC)-Induced Rapid Growth, Proton Extrusion and Membrane Potential Changes in Maize (Zea mays L.) Coleoptile Cells: Comparison to Auxin Responses

2021 ◽  
Vol 22 (9) ◽  
pp. 5017
Author(s):  
Małgorzata Polak ◽  
Waldemar Karcz
Keyword(s):  
Membrane Potential ◽  
Rapid Growth ◽  
Proton Pumps ◽  
Proton Extrusion ◽  
Membrane Hyperpolarization ◽  
Fungal Toxin ◽  
Maize Coleoptile ◽  
Lag Times ◽  
Kinetics Of ◽  
Indole 3 Acetic Acid

The fungal toxin fusicoccin (FC) induces rapid cell elongation, proton extrusion and plasma membrane hyperpolarization in maize coleoptile cells. Here, these three parameters were simultaneously measured using non-abraded and non-peeled segments with the incubation medium having access to their lumen. The dose–response curve for the FC-induced growth was sigmoidal shaped with the maximum at 10−6 M over 10 h. The amplitudes of the rapid growth and proton extrusion were significantly higher for FC than those for indole-3-acetic acid (IAA). The differences between the membrane potential changes that were observed in the presence of FC and IAA relate to the permanent membrane hyperpolarization for FC and transient hyperpolarization for IAA. It was also found that the lag times of the rapid growth, proton extrusion and membrane hyperpolarization were shorter for FC compared to IAA. At 30 °C, the biphasic kinetics of the IAA-induced growth rate could be changed into a monophasic (parabolic) one, which is characteristic for FC-induced rapid growth. It has been suggested that the rates of the initial phase of the FC- and IAA-induced growth involve two common mechanisms that consist of the proton pumps and potassium channels whose contribution to the action of both effectors on the rapid growth is different.

Opioid-Activated Postsynaptic, Inward Rectifying Potassium Currents in Whole Cell Recordings in Substantia Gelatinosa Neurons

1998 ◽  
Vol 80 (6) ◽  
pp. 2954-2962 ◽  
Author(s):  
S. P. Schneider ◽  
W. A. Eckert ◽  
A. R. Light
Keyword(s):  
Membrane Potential ◽  
G Protein ◽  
Potassium Currents ◽  
Substantia Gelatinosa ◽  
Opioid Agonist ◽  
Membrane Hyperpolarization ◽  
Whole Cell ◽  
Protein Activation ◽  
G Protein Activation ◽  
Whole Cell Recordings

Schneider, S. P., W. A. Eckert III, and A. R. Light. Opioid-activated postsynaptic, inward rectifying potassium currents in whole cell recordings in substantia gelatinosa neurons. J. Neurophysiol. 80: 2954–2962, 1998. Using tight-seal, whole cell recordings from isolated transverse slices of hamster and rat spinal cord, we investigated the effects of the μ-opioid agonist (d-Ala2, N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO) on the membrane potential and conductance of substantia gelatinosa (SG) neurons. We observed that bath application of 1–5 μM DAMGO caused a robust and repeatable hyperpolarization in membrane potential ( V m) and decrease in neuronal input resistance ( R N) in 60% (27/45) of hamster neurons and 39% (9/23) of rat neurons, but significantly only when ATP (2 mM) and guanosine 5′-triphosphate (GTP; 100 μM) were included in the patch pipette internal solution. An ED50 of 50 nM was observed for the hyperpolarization in rat SG neurons. Because G-protein mediation of opioid effects has been shown in other systems, we tested if the nucleotide requirement for opioid hyperpolarization in SG neurons was due to G-protein activation. GTP was replaced with the nonhydrolyzable GTP analogue guanosine-5′- O-(3-thiotriphosphate) (GTP-γ-S; 100 μM), which enabled DAMGO to activate a nonreversible membrane hyperpolarization. Further, intracellular application of guanosine-5′- O-(2-thiodiphosphate) (GDP-β-S; 500 μM), which blocks G-protein activation, abolished the effects of DAMGO. We conclude that spinal SG neurons are particularly susceptible to dialysis of GTP by whole cell recording techniques. Moreover, the depletion of GTP leads to the inactivation of G-proteins that mediate μ-opioid activation of an inward-rectifying, potassium conductance in these neurons. These results explain the discrepancy between the opioid-activated hyperpolarization in SG neurons observed in previous sharp electrode experiments and the more recent failures to observe these effects with whole cell patch techniques.

scholarly journals Injection of inositol trisphosphorothioate into Limulus ventral photoreceptors causes oscillations of free cytosolic calcium.

1991 ◽  
Vol 97 (6) ◽  
pp. 1165-1186 ◽  
Author(s):  
R Payne ◽  
B V Potter
Keyword(s):  
Membrane Potential ◽  
Calcium Release ◽  
Feedback Inhibition ◽  
Initial Response ◽  
Periodic Variation ◽  
Cytosolic Calcium ◽  
Ion Concentration ◽  
Free Calcium ◽  
Calcium Stores ◽  
Calcium Ion Concentration

Limulus ventral photoreceptors contain calcium stores sensitive to release by D-myo-inositol 1,4,5 trisphosphate (InsP3) and a calcium-activated conductance that depolarizes the cell. Mechanisms that terminate the response to InsP3 were investigated using nonmetabolizable DL-myo-inositol 1,4,5 trisphosphorothioate (InsPS3). An injection of 1 mM InsPS3 into a photoreceptor's light-sensitive lobe caused an initial elevation of cytosolic free calcium ion concentration (Cai) and a depolarization lasting only 1-2 s. A period of densensitization followed, during which injections of InsPS3 were ineffective. As sensitivity recovered, oscillations of membrane potential began, continuing for many minutes with a frequency of 0.07-0.3 Hz. The activity of InsPS3 probably results from the D-stereoisomer, since L-InsP3 was much less effective than InsP3. Injections of 1 mM InsP3 caused an initial depolarization and a period of densensitization similar to that caused by 1 mM InsPS3, but no sustained oscillations of membrane potential. The initial response to InsPS3 or InsP3 may therefore be terminated by densensitization, rather than by metabolism. Metabolism of InsP3 may prevent oscillations of membrane potential after sensitivity has recovered. The InsPS3-induced oscillations of membrane potential accompanied oscillations of Cai and were abolished by injection of ethyleneglycol-bis (beta-aminoethyl ether)-N,N'-tetraacetic acid. Removal of extracellular calcium reduced the frequency of oscillation but not its amplitude. Under voltage clamp, oscillations of inward current were observed. These results indicate that periodic bursts of calcium release underly the oscillations of membrane potential. After each burst, the sensitivity of the cell to injected InsP3 was greatly reduced, recovering during the interburst interval. The oscillations may, therefore, result in part from a periodic variation in sensitivity to a constant concentration of InsPS3. Prior injection of calcium inhibited depolarization by InsPS3, suggesting that feedback inhibition of InsPS3-induced calcium release by elevated Cai may mediate desensitization between bursts and after injections of InsPS3.

scholarly journals Cytoplasmic [Ca2+] and intracellular pH in lymphocytes. Role of membrane potential and volume-activated Na+/H+ exchange.

1987 ◽  
Vol 89 (2) ◽  
pp. 185-213 ◽  
Author(s):  
S Grinstein ◽  
S Cohen
Keyword(s):  
Protein Kinase C ◽  
Membrane Potential ◽  
Protein Kinase ◽  
Intracellular Ph ◽  
Enzyme Treatment ◽  
Membrane Hyperpolarization ◽  
Kinase C ◽  
Free Media ◽  
Stimulation Of

The effect of elevating cytoplasmic Ca2+ [( Ca2+]i) on the intracellular pH (pHi) of thymic lymphocytes was investigated. In Na+-containing media, treatment of the cells with ionomycin, a divalent cation ionophore, induced a moderate cytoplasmic alkalinization. In the presence of amiloride or in Na+-free media, an acidification was observed. This acidification is at least partly due to H+ (equivalent) uptake in response to membrane hyperpolarization since: it was enhanced by pretreatment with conductive protonophores, it could be mimicked by valinomycin, and it was decreased by depolarization with K+ or gramicidin. In addition, activation of metabolic H+ production also contributes to the acidification. The alkalinization is due to Na+/H+ exchange inasmuch as it is Na+ dependent, amiloride sensitive, and accompanied by H+ efflux and net Na+ gain. A shift in the pHi dependence underlies the activation of the antiport. The effect of [Ca2+]i on Na+/H+ exchange was not associated with redistribution of protein kinase C and was also observed in cells previously depleted of this enzyme. Treatment with ionomycin induced significant cell shrinking. Prevention of shrinking largely eliminated the activation of the antiport. Moreover, a comparable shrinking produced by hypertonic media also activated the antiport. It is concluded that stimulation of Na+/H+ exchange by elevation of [Ca2+]i is due, at least in part, to cell shrinking and does not require stimulation of protein kinase C.

Cellular and subcellular mechanisms of cardiac pacemaker oscillations

1979 ◽  
Vol 81 (1) ◽  
pp. 205-215
Author(s):  
R. W. Tsien ◽  
R. S. Kass ◽  
R. Weingart
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Surface Membrane ◽  
Cardiac Pacemaker ◽  
Oscillatory Activity ◽  
Purkinje Fibre ◽  
Pacemaker Activity ◽  
Heart Cells ◽  
Control Loop ◽  
Internal Oscillation

Rhythmic oscillations in the membrane potential of heart cells are important in normal cardiac pacemaker activity as well as cardiac arrhythmias. Two fundamentally different mechanisms of oscillatory activity can be distinguished at the cellular and subcellular level. The first mechanism, referred to as a surface membrane oscillator, can be represented by a control loop in which membrane potential changes evoke delayed conductance changes and vice versa. Since the surface membrane potential is a key variable within the control loop, the oscillation can be interrupted at any time by holding the membrane potential constant with a voltage clamp. This mode of oscillation seems to describe spontaneous pacemaker activity in the primary cardiac pacemaker (sinoatrial node) as well as other regions (Purkinje fibre, atrial or ventricular muscle). In all tissues studied so far, the pacemaker depolarization is dominated by the slow shutting-off of an outward current, largely carried by potassium ions. The second mechanism can be called an internal oscillator since it depends upon a subcellular rhythm generator which is largely independent from the surface membrane. Under voltage clamp, the existence of the internal oscillation is revealed by the presence of oscillations in membrane conductance or contractile force which occur even though the membrane potential is held fixed. The two oscillatory mechanisms are not mutually exclusive; the subcellular mechanism can be preferentially enhanced in any given cardiac cell by conditions which elevate intracellular calcium. Such conditions include digitalis intoxication, high Cao, low Nao, low or high Ko, cooling, or rapid stimulation. Several lines of evidence suggest that the subcellular mechanism involves oscillatory variations in myoplasmic calcium, probably due to cycles of Ca uptake and release by the sarcoplasmic reticulum. The detailed nature of the Cai oscillator and its interaction with the surface membrane await further investigation.

Abstract 9411: Urine Aquaporin-2 Level is a Novel Marker for the Better Prognosis After Long-Term Tolvaptan Treatment in Patients With Advanced Heart Failure

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Teruhiko Imamura ◽  
Koichiro Kinugawa ◽  
Takeo Fujino ◽  
Toshiro Inaba ◽  
Hisataka Maki ◽  
...  
Keyword(s):  
Heart Failure ◽  
De Novo ◽  
Collecting Duct ◽  
Initial Response ◽  
Aquaporin 2 ◽  
Long Term Treatment ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Introduction: Preserved function of collecting duct is essential for the response to tolvaptan (TLV), and urinary level of aquaporin 2 (U-AQP2) can be a marker for vasopressin-dependent activity of collecting duct. Hypothesis: Higher levels of U-AQP2 in proportion to plasma levels of vasopressin (P-AVP) may be associated with better initial responses to TLV and eventually result in the improved prognosis after long-term treatment of TLV. Methods: Consecutive 60 in-hospital patients with stage D heart failure (HF) who received TLV on a de novo basis were enrolled during 2011-2013. We also selected 60 HF patients by propensity score matching who were hospitalized during the same period but never treated with TLV. Events were defined as death and/or HF re-hospitalization. Results: TLV (3.75-15 mg/day) was continuously administered except death or ventricular assist device implantation occurred. There were 41 patients (group 1) who had increases in UV over the first 24 h after TLV initiation, and all of them had U-AQP2/P-AVP ≥0.5 х103 with higher U-AQP2 levels (5.42 ± 3.54 ng/mL) before TLV treatment. On the other hand, UV rather decreased even after TLV initiation in 19 patients over the first 24 h (group 2). Those in the group 2 universally had U-AQP2/P-AVP <0.5 х103, extremely low U-AQP2 levels (0.76 ± 0.59 ng/mL, p<0.001 vs. group 1), and similar P-AVP with the group 1 at baseline. The 41 and 19 patients without TLV treatment (group 3 and 4) were respectively matched to the group 1 and 2 by propensity scores. Interestingly, every patient in the group 3 had U-AQP2/P-AVP ≥0.5 х103, and vice versa in the group 4. Among the four groups, congestion-related symptoms were only improved in the group 1 after 1 month of enrollment. The patients in the group 1 had significantly better event-free survival over 2-year by TLV treatment compared with the group 3 (76% vs. 43%, p<0.014). In contrast, the patients in the group 2 and 4 had very poor prognoses regardless of TLV treatment (7% vs. 11%, p=0.823). Conclusions: U-AQP2/P-AVP is a novel predictor for the initial response to TLV in HF patients. Patients with higher U-AQP2/P-AVP may enjoy a better prognosis by long-term TLV treatment probably due to efficient resolution of congestion.

Prognostic significance of surface marker expression on blasts of patients with de novo acute myeloblastic leukemia.

1990 ◽  
Vol 8 (3) ◽  
pp. 423-430 ◽  
Author(s):  
I Schwarzinger ◽  
P Valent ◽  
U Köller ◽  
C Marosi ◽  
B Schneider ◽  
...  
Keyword(s):  
Complete Remission ◽  
De Novo ◽  
Surface Membrane ◽  
Survival Rates ◽  
Prognostic Significance ◽  
Acute Myeloblastic Leukemia ◽  
Probability Of Survival ◽  
Surface Marker Expression ◽  
Median Period ◽  
De Novo Aml

The prognostic significance of the expression of surface membrane antigens on the blasts of 123 consecutive patients with de novo acute myeloblastic leukemia (AML) was evaluated. For this purpose, reactivity of monoclonal antibodies (mAbs) CLB-ERY3 (antiblood-group H antigen), VIM-D5 (CD15), WT1 (CD7), MY7 (CD13), MY9 (CD33), VID-1 (antihuman leukocyte antigen locus DR [anti-HLA DR]), VIM-2 (CDw65L), VIM-13 (CD14), 63D3 (CD14) and anti-TdT with leukemic blast cell populations was prospectively analyzed with respect to the rates of complete remission (CR), continuous complete remission (CCR), and survival. The overall rate of CR was 65%, the 6-year rates of overall CCR and survival were 23% and 13%, respectively (median period of patient observation, 30 months). Of all Abs tested, four (CLB-ERY3, MY7, anti-TdT, and VIM-D5) were found to be of prognostic value. Reactivity of CLB-ERY3, MY7, and anti-TdT was predictive for CR (CLB-ERY3+, 43% v CLB-ERY3-, 73%, P less than .02; MY7+, 59% v MY7-, 91%, P less than .003; TdT+, 28% v TdT-, 71%, P less than .001, respectively) and probability of survival (significantly lower survival rates: CLB-ERY3+, P less than .02; MY7+, P less than .03; and TdT+ cases, P less than .001, respectively). Reactivity of VIM-D5 was significantly associated with a higher probability of CCR (P less than .01). Our results confirm earlier reports on the prognostic significance of expression of CD13 and TdT in AML and indicate CLB-ERY3 (antiblood-group H antibody) and VIM-D5 (CD15) as further markers predictive for the clinical outcome in patients with de novo AML.

Conductance changes underlying a late synaptic hyperpolarization in hippocampal CA3 neurons

1987 ◽  
Vol 58 (1) ◽  
pp. 160-179 ◽  
Author(s):  
J. J. Hablitz ◽  
R. H. Thalmann
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Time Course ◽  
Membrane Potentials ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Voltage Sensitivity ◽  
Base Line ◽  
Membrane Hyperpolarization ◽  
Ca3 Neurons

1. Single-electrode current- and voltage-clamp techniques were employed to study properties of the conductance underlying an orthodromically evoked late synaptic hyperpolarization or late inhibitory postsynaptic potential (IPSP) in CA3 pyramidal neurons in the rat hippocampal slice preparation. 2. Late IPSPs could occur without preceding excitatory postsynaptic potentials at the resting membrane potential and were graded according to the strength of the orthodromic stimulus. The membrane hyperpolarization associated with the late IPSP peaked within 140-200 ms after orthodromic stimulation of mossy fiber afferents. The late IPSP returned to base line with a half-decay time of approximately 200 ms. 3. As determined from constant-amplitude hyperpolarizing-current pulses, the membrane conductance increase during the late IPSP, and the time course of its decay, were similar whether measurements were made near the resting membrane potential or when the cell was hyperpolarized by approximately 35 mV. 4. When 1 mM cesium was added to the extracellular medium to reduce inward rectification, late IPSPs could be examined over a range of membrane potentials from -60 to -140 mV. For any given neuron, the late IPSP amplitude-membrane potential relationship was linear over the same range of membrane potentials for which the slope input resistance was constant. The late IPSP reversed symmetrically near -95 mV. 5. Intracellular injection of ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid or extracellular application of forskolin, procedures known to reduce or block certain calcium-dependent potassium conductances in CA3 neurons, had no significant effect on the late IPSP. 6. Single-electrode voltage-clamp techniques were used to analyze the time course and voltage sensitivity of the current underlying the late IPSP. This current [the late inhibitory postsynaptic current (IPSC)] began as early as 25 ms after orthodromic stimulation and reached a peak 120-150 ms following stimulation. 7. The late IPSC decayed with a single exponential time course (tau = 185 ms). 8. A clear reversal of the late IPSC at approximately -99 mV was observed in a physiological concentration of extracellular potassium (3.5 mM).(ABSTRACT TRUNCATED AT 400 WORDS)

Partial Uncoupling of Neurotransmitter Release From [Ca2+]i by Membrane Hyperpolarization

1999 ◽  
Vol 81 (6) ◽  
pp. 3044-3053 ◽  
Author(s):  
R. Ravin ◽  
H. Parnas ◽  
M. E. Spira ◽  
I. Parnas
Keyword(s):  
Membrane Potential ◽  
Neurotransmitter Release ◽  
Quantal Content ◽  
Presynaptic Membrane ◽  
Release Process ◽  
Membrane Hyperpolarization ◽  
Quantal Release ◽  
Asynchronous Release ◽  
Frequency Of Stimulation ◽  
Different Levels

Partial uncoupling of neurotransmitter release from [Ca2+]i by membrane hyperpolarization. The dependence of evoked and asynchronous release on intracellular calcium ([Ca2+]i) and presynaptic membrane potential was examined in single-release boutons of the crayfish opener neuromuscular junction. When a single bouton was depolarized by a train of pulses, [Ca2+]iincreased to different levels according to the frequency of stimulation. Concomitant measurements of evoked release and asynchronous release, from the same bouton, showed that both increased in a sigmoidal manner as a function of [Ca2+]i. When each of the depolarizing pulses was immediately followed by a hyperpolarizing pulse, [Ca2+]i was elevated to a lesser degree than in the control experiments, and the rate of asynchronous release and the quantal content were reduced; most importantly, evoked quantal release terminated sooner. The diminution of neurotransmitter release by the hyperpolarizing postpulse (HPP) could not be entirely accounted for by the reduction in [Ca2+]i. The experimental results are consistent with the hypothesis that the HPP reduces the sensitivity of the release machinery to [Ca2+]i, thereby not only reducing the quantal content but also terminating the quantal release process sooner.

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