Influence of long-chain acylcarnitines on voltage-dependent calcium current in adult ventricular myocytes

1992 ◽  
Vol 263 (2) ◽  
pp. H410-H417 ◽  
Author(s):  
J. Wu ◽  
P. B. Corr
Keyword(s):  
Calcium Current ◽  
Ventricular Myocytes ◽  
Indirect Evidence ◽  
Cell Voltage ◽  
Time Dependent ◽  
Similar Degree ◽  
Tetraacetic Acid ◽  
Voltage Dependent ◽  
Long Chain

Long-chain acylcarnitines (LCAC) increase 3.5-fold within 2 min in ischemic myocardium in vivo, and previous studies have suggested, through indirect evidence, that LCAC can stimulate the voltage-dependent L-type Ca2+ current [ICa(L)] in both cardiac and smooth muscle cells. In the present study, whole cell voltage-clamp procedures were performed in isolated adult guinea pig ventricular myocytes to assess the direct effect of LCAC on ICa(L). The intracellular solution contained (in mM) 80 CsCl, 40 K-aspartic acid, and 5 ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). Maximal current density of ICa(L) at 0 mV was 10.1 +/- 0.5 pA/pF (n = 22) at extracellular Ca2+ concentration ([Ca2+]o) = 2.7 mM. LCAC induced a concentration (1-25 microM, n = 23)- and time-dependent, reversible decrease in ICa(L). When delivered extracellularly for 10 min, LCAC (5 microM) inhibited the maximal current of ICa(L) by 48.1 +/- 1.3% (n = 9, P less than 0.01) and shifted the half-maximal voltage of steady-state activation and inactivation from -13.1 +/- 0.5 to -6.8 +/- 0.4 mV (n = 4; P less than 0.05) and from -21.8 +/- 0.2 to -16.5 +/- 0.6 mV (n = 4; P less than 0.01), respectively. Intracellular delivery of LCAC (5 microM) also suppressed ICa(L) to a similar degree (47.5 +/- 1.5%, n = 4; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Targeted inactivation of Gαi does not alter cardiac function or β-adrenergic sensitivity

2001 ◽  
Vol 280 (2) ◽  
pp. H569-H575 ◽  
Author(s):  
Mohit Jain ◽  
Chee Chew Lim ◽  
Kohzo Nagata ◽  
Vannessa M. Davis ◽  
David S. Milstone ◽  
...  
Keyword(s):  
Cardiac Function ◽  
Ventricular Myocytes ◽  
Ex Vivo ◽  
Cardiac Response ◽  
Similar Degree ◽  
Wild Type ◽  
Isolated Hearts ◽  
Targeted Inactivation ◽  
Contractile Performance

Inhibitory Gαi protein increases in the myocardium during hypertrophy and has been associated with β-adrenergic receptor (β-AR) desensitization, contractile dysfunction, and progression of cardiac disease. The role of Gαi proteins in mediating basal cardiac function and β-AR response in nonpathological myocardium, however, is uncertain. Transgenic mice with targeted inactivation of Gαi2 or Gαi3 were examined for in vivo cardiac function with the use of conscious echocardiography and for ex vivo cardiac response to inotropic stimulation with the use of Langendorff blood-perfused isolated hearts and adult ventricular cardiomyocytes. Echocardiography revealed that percent fractional shortening and heart rate were similar among wild-type, Gαi2 -null, and Gαi3 -null mice. Comparable baseline diastolic and contractile performance was also observed in isolated hearts and isolated ventricular myocytes from wild-type mice and mice lacking Gαi proteins. Isoproterenol infusion enhanced diastolic and contractile performance to a similar degree in wild-type, Gαi2 -null, and Gαi3 -null mice. These data demonstrate no observable role for inhibitory G proteins in mediating basal cardiac function or sensitivity to β-AR stimulation in nonpathological myocardium.

scholarly journals Loss of Rad-GTPase produces a novel adaptive cardiac phenotype resistant to systolic decline with aging

2015 ◽  
Vol 309 (8) ◽  
pp. H1336-H1345 ◽  
Author(s):  
Janet R. Manning ◽  
Catherine N. Withers ◽  
Bryana Levitan ◽  
Jeffrey D. Smith ◽  
Douglas A. Andres ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cardiac Output ◽  
Calcium Current ◽  
Ventricular Myocytes ◽  
Morphological Changes ◽  
Heart Function ◽  
Early Time ◽  
Cardiac Phenotype ◽  
Systolic And Diastolic Function

Rad-GTPase is a regulator of L-type calcium current (LTCC), with increased calcium current observed in Rad knockout models. While mouse models that result in elevated LTCC have been associated with heart failure, our laboratory and others observe a hypercontractile phenotype with enhanced calcium homeostasis in Rad−/−. It is currently unclear whether this observation represents an early time point in a decompensatory progression towards heart failure or whether Rad loss drives a novel phenotype with stable enhanced function. We test the hypothesis that Rad−/− drives a stable nonfailing hypercontractile phenotype in adult hearts, and we examine compensatory regulation of sarcoplasmic reticulum (SR) loading and protein changes. Heart function was measured in vivo with echocardiography. In vivo heart function was significantly improved in adult Rad−/− hearts compared with wild type. Heart wall dimensions were significantly increased, while heart size was decreased, and cardiac output was not changed. Cardiac function was maintained through 18 mo of age with no decompensation. SR releasable Ca2+ was increased in isolated Rad−/− ventricular myocytes. Higher Ca2+ load was accompanied by sarco/endoplasmic reticulum Ca2+ ATPase 2a (SERCA2a) protein elevation as determined by immunoblotting and a rightward shift in the thapsigargan inhibitor-response curve. Rad−/− promotes morphological changes accompanied by a stable increase in contractility with aging and preserved cardiac output. The Rad−/− phenotype is marked by enhanced systolic and diastolic function with increased SR uptake, which is consistent with a model that does not progress into heart failure.

Succinylcholine Metabolite Succinic Acid Alters Steady State Activation in Muscle Sodium Channels

2000 ◽  
Vol 92 (5) ◽  
pp. 1385-1391 ◽  
Author(s):  
Gertrud Haeseler ◽  
Jacqueline Petzold ◽  
Hartmut Hecker ◽  
Axel Würz ◽  
Reinhard Dengler ◽  
...  
Keyword(s):  
Steady State ◽  
Succinic Acid ◽  
Sodium Channels ◽  
Animal Experiments ◽  
Cell Voltage ◽  
Hek293 Cells ◽  
Muscle Rigidity ◽  
Voltage Dependent

Background Animal experiments revealed that succinylcholine produced masseter muscle rigidity and activated myotonic discharges despite neuromuscular blockade with a nondepolarizing blocker. These results suggest that either succinylcholine or its metabolites might interfere directly with voltage-operated ion channels of the sarcolemma. The aim of this study was to examine effects of one product of succinylcholine hydrolysis, succinic acid, on voltage-gated muscle sodium (Na+) channels. Methods Alpha subunits of human muscle sodium channels were heterologously expressed in HEK293 cells. Activation of Na+ currents was examined applying standard whole-cell voltage-clamp protocols in the absence (control and washout) and presence of succinic acid in different concentrations (0.05-10 mm). Results Succinic acid shifted the midpoints of steady state activation plots in the direction of more negative test potentials, indicating that channels open during smaller depolarizations in the presence of the drug. The maximum amount of the negative shift in 10 mm succinic acid was -6.3 +/- 1.7 mV; the EC50 for this effect was 0.39 mm. In addition, succinic acid (10 mm) significantly enhanced maximum currents after depolarizations with respect to a series of control experiments. Conclusion Succinic acid facilitates voltage-dependent activation in muscle sodium channels in vitro. This might lead to muscle hyperexcitability in vivo.

Oxytocin actions on voltage-dependent ionic channels in pregnant rat uterine smooth muscle cells

1992 ◽  
Vol 70 (12) ◽  
pp. 1597-1603 ◽  
Author(s):  
Yoshihito Inoue ◽  
Keiichi Shimamura ◽  
Nicholas Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Voltage Clamp ◽  
Calcium Current ◽  
Uterine Contraction ◽  
Cell Voltage ◽  
Ionic Channels ◽  
Pregnant Rat ◽  
Uterine Smooth Muscle ◽  
Voltage Dependent ◽  
Sodium And Potassium

The effects of oxytocin, a uterotonic polypeptide hormone, on the voltage-dependent slow calcium, fast sodium, and potassium channel currents were studied using whole-cell voltage clamp of freshly isolated cells from late pregnant (18–21 day) rat myometrium. The calcium current was rapidly inhibited by oxytocin (about 25% inhibition at 20 nM) in a dose-dependent manner, and this inhibitory effect was completely reversible by washout. However, inhibition was not observed when barium was used as the charge carrier. Sodium current and potassium current were not modified by oxytocin, thus sodium and potassium currents may not play important roles in oxytocin-induced augmentation of uterine contraction. It is concluded that oxytocin stimulates uterine contraction by mechanisms other than augmentation of the voltage-dependent calcium current, e.g., by release of Ca from sarcoplasmic reticulum (by inositol trisphosphate) or by activation of a receptor-operated Ca channel. The inhibition of the slow calcium current may be induced by the elevation of [Ca]i.Key words: oxytocin, ionic channels, uterine smooth muscle, whole-cell voltage clamp, pregnant rat myometrium.

Channels involved in transient currents unmasked by removal of extracellular calcium in cardiac cells

2002 ◽  
Vol 282 (5) ◽  
pp. H1879-H1888 ◽  
Author(s):  
Regina Macianskiene ◽  
Francesco Moccia ◽  
Karin R. Sipido ◽  
Willem Flameng ◽  
Kanigula Mubagwa
Keyword(s):  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Monovalent Cation ◽  
Cardiac Cells ◽  
Time Dependent ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
High Concentrations ◽  
Low Sensitivity

In cardiac cells that lack macroscopic transient outward K+ currents ( I to), the removal of extracellular Ca2+ can unmask “ I to-like” currents. With the use of pig ventricular myocytes and the whole cell patch-clamp technique, we examined the possibility that cation efflux via L-type Ca2+channels underlies these currents. Removal of extracellular Ca2+ and extracellular Mg2+ induced time-independent currents at all potentials and time-dependent currents at potentials greater than −50 mV. Either K+ or Cs+ could carry the time-dependent currents, with reversal potential of +8 mV with internal K+ and +34 mV with Cs+. Activation and inactivation were voltage dependent [Boltzmann distributions with potential of half-maximal value ( V 1/2) = −24 mV and slope = −9 mV for activation; V 1/2 = −58 mV and slope = 13 mV for inactivation]. The time-dependent currents were resistant to 4-aminopyridine and to DIDS but blocked by nifedipine at high concentrations (IC50 = 2 μM) as well as by verapamil and diltiazem. They could be increased by BAY K-8644 or by isoproterenol. We conclude that the I to-like currents are due to monovalent cation flow through L-type Ca2+ channels, which in pig myocytes show low sensitivity to nifedipine.

Characterization of macroscopic outward currents of canine colonic myocytes

1989 ◽  
Vol 257 (3) ◽  
pp. C461-C469 ◽  
Author(s):  
W. C. Cole ◽  
K. M. Sanders
Keyword(s):  
Outward Current ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Voltage Dependent ◽  
K Current ◽  
Time Courses

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

Inhibition of the voltage-dependent calcium current by extracellular ATP in hamster ventricular cardiomyocytes

1997 ◽  
Vol 273 (1) ◽  
pp. H250-H256 ◽  
Author(s):  
F. Von zur Muhlen ◽  
B. D. Gonska ◽  
H. Kreuzer
Keyword(s):  
Calcium Current ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Purinergic Receptor ◽  
Extracellular Atp ◽  
Patch Clamp Technique ◽  
Ventricular Cardiomyocytes ◽  
Current Voltage ◽  
Voltage Dependent ◽  
High Level

The modulation of the high-voltage-activated calcium current (ICa) by external ATP was examined in single ventricular cardiomyocytes of the hamster using the whole-cell configuration of the patch-clamp technique. Extracellular application of ATP (0.1-100 microM) was found to inhibit ICa reversibly. The inhibition followed a slow time course (half time approximately 25 s) and was accompanied by very small changes of the holding current and no shift in the current-voltage relationship. With 100 microM ATP, peak ICa was reduced by approximately 30%. This response was not blocked by the P1 inhibitor 8-cyclopentyl-1,3-dipropylxanthine. The nonhydrolyzable ATP analogs adenosine 5'-O-(3-thiotriphosphate) and AMP-adenosine 5'-[beta,gamma-imido]triphosphate also reduced ICa. The ATP analog alpha,beta-methylene-ATP was about equipotent with ATP at 50 microM. Internal guanosine 5'-O-(3-thiotriphosphate) (200 microM) rendered the ATP-mediated inhibition of ICa poorly reversible, whereas internal guanosine 5'-O-(2-thiodiphosphate) (200-500 microM) had no effect. Holding the intracellular adenosine 3',5'-cyclic monophosphate concentration at a constant high level did not alter the ATP response. We conclude that external ATP inhibits ICa via a P2 purinergic receptor in hamster ventricular myocytes. Our results suggest the involvement of a G protein not coupled to adenylate cyclase. The inhibition of ICa by extracellular ATP might have pathophysiological relevance under conditions of myocardial injury.

Three distinct G protein pathways mediate inhibition of neuronal calcium current by bradykinin

1996 ◽  
Vol 76 (5) ◽  
pp. 3559-3562 ◽  
Author(s):  
M. A. Wilk-Blaszczak ◽  
W. D. Singer ◽  
F. Belardetti
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Calcium Current ◽  
Suppressive Effect ◽  
Calcium Currents ◽  
Tetraacetic Acid ◽  
Combined Application ◽  
Voltage Dependent ◽  
K Currents

1. In NG108-15 cells dialyzed with 10 mM ethylene glycolbis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or bis (o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), bradykinin (BK) selectively inhibited the N-type calcium current. This effect of BK was blocked by an antibody directed against the G protein G13. Thus under these conditions G13 mediates the inhibition of voltage-dependent calcium current (ICa, V) by BK. In contrast, activation of K+ currents by BK is mediated by Gq/11. BK also couples to Gi2. 2. We now examine the involvement of G proteins in the inhibition of ICa, V by BK when NG108-15 cells are dialyzed with 1 mM BAPTA. Under these conditions, BK inhibited both the N- and L-type, but not the T-type, calcium currents. Intracellular application of anti-G13 antibody did not suppress the response to BK. Applications of either anti-Gq/11 antibody or pertussis toxin (PTX, to block Gi2) were similarly ineffective. Even combined application of anti-Gq/11 and -G13 antibodies, or PTX together with either antibody, did not block inhibition of ICa, V by BK. However, the combination of both antibodies with PTX blocked the response to BK in low BAPTA. In conclusion, both Gq/11 and a PTX-sensitive G protein (presumably Gi2), together with G13, are involved in the inhibition of ICa, V by BK. 3. Gq/11 inhibited only the L-type calcium current, whereas the PTX-sensitive G protein inhibited both the N- and L-type calcium currents. 4. The BAPTA dependence of the Gq/11 and PTX-sensitive inhibitions may reflect a Ca2+ requirement of the pathway(s) acting on the L current and/or a direct suppressive effect of BAPTA.

Serotonin Modulates Voltage-Dependent Calcium Current in Necturus Taste Cells

1997 ◽  
Vol 77 (5) ◽  
pp. 2515-2524 ◽  
Author(s):  
Rona J. Delay ◽  
Sue C. Kinnamon ◽  
Stephen D. Roper
Keyword(s):  
Calcium Current ◽  
Taste Receptor ◽  
Cell Voltage ◽  
Nerve Fibers ◽  
Receptor Subtype ◽  
Basal Cells ◽  
Receptor Cells ◽  
Taste Cells ◽  
Voltage Dependent ◽  
Taste Receptor Cells

Delay, Rona J., Sue C. Kinnamon, and Stephen D. Roper. Serotonin modulates voltage-dependent calcium current in Necturus taste cells. J. Neurophysiol. 77: 2515–2524, 1997. Necturus taste buds contain two primary cell types: taste receptor cells and basal cells. Merkel-like basal cells are a subset of basal cells that form chemical synapses with taste receptor cells and with innervating nerve fibers. Although Merkel-like basal cells cannot interact directly with taste stimuli, recent studies have shown that Merkel-like basal cells contain serotonin (5-HT), which may be released onto taste receptor cells in response to taste stimulation. With the use of whole cell voltage clamp, we examined whether focal applications of 5-HT to isolated taste receptor cells affected voltage-activated calcium current ( I Ca). Two different effects were observed. 5-HT at 100 μM increased I Ca in 33% of taste receptor cells, whereas it decreased I Ca in 67%. Both responses used a 5-HT receptor subtype with a pharmacological profile similar to that of the 5-HT1A receptor, but the potentiation and inhibition of I Ca by 5-HT were mediated by two different second-messenger cascades. The results indicate that functional subtypes of taste receptor cells, earlier defined only by their sensitivity to taste stimuli, may also be defined by their response to the neurotransmitter 5-HT and suggest that 5-HT released by Merkel-like basal cells could modulate taste receptor function.

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