Cloning of a carrot cDNA for a member of the family of ADP-ribosylation factors (ARFs) and characterization of the binding of nucleotides by its product after expression in E. coli

A cDNA clone, designated DcArf1, was isolated from a cDNA library prepared from embryogenic cell clusters of Daucus carota and characterized. The cDNA (883 bp) contained an open reading frame that encoded a protein of 181 amino acid residues with significant homology to the ADP-ribosylation factors (ARFs) of animals and yeast. The DcArf1-related transcripts were detected at a nearly constant level during somatic embryogenesis. The DcArf1-encoded protein was expressed as a fusion protein in E. coli and was shown to have dithiothreitol-independent [alpha-32P]GTP-binding activity. This binding was completely prevented by a 100-fold molar excess of unlabeled GTP or GDP, while GMP, ANP, TNP, CNP and UNP had no effect on the binding. The binding of [35S]GTP gamma S to the recombinant DCARF1 protein was detected only in the presence of millimolar levels of both MgCl2 and dimyristoylphosphatidylcholine (DMPC). The amino acid sequence and the GTP-binding characteristics of the DCARF1 protein suggest that the DcArf1 cDNA encodes an ARF of carrot rather than a protein that only resembles such a factor, ADP-ribosylation factor-like protein (ARL).

Correlation between the induction of a gene for delta 1-pyrroline-5-carboxylate synthetase and the accumulation of proline in Arabidopsis thaliana under osmotic stress

The isolation and characterization is reported of a cDNA for delta 1-pyrroline-5-carboxylate (P5C) synthetase (cAtP5CS), an enzyme involved in the biosynthesis of proline, from a cDNA library prepared from a dehydrated rosette plant of Arabidopsis thaliana. Southern blot analysis suggested that only one copy of the corresponding gene (AtP5CS) is present in A. thaliana. The deduced amino acid sequence of the P5CS protein (AtP5CS) from A. thaliana exhibited 74% homology to that of the P5CS from Vigna aconitifolia. Northern blot analysis revealed that the gene for P5CS was induced by dehydration, high salt and treatment with ABA, while it was not induced by heat or cold treatment. Moreover, the simultaneous accumulation of proline was observed as a result of the former treatments in A. thaliana. A cDNA for P5C reductase (cAtP5CR) was also isolated from A. thaliana and Northern blot analysis was performed. The AtP5CR gene was not induced to a significant extent by dehydration or high-salt stress. These observations suggest that the AtP5CS gene plays a principal role in the biosynthesis of proline in A. thaliana under osmotic stress.

Gene evolution of epoxide hydrolases and recommended nomenclature

We have analyzed amino acid sequence relationships among soluble and microsomal epoxide hydrolases, haloacid dehalogenases, and a haloalkane dehalogenase. The amino-terminal residues (1-229) of mammalian soluble epoxide hydrolase are homologous to a haloacid dehalogenase. The carboxy-terminal residues (230-554) of mammalian soluble epoxide hydrolase are homologous to haloalkane dehalogenase, to plant soluble epoxide hydrolase, and to microsomal epoxide hydrolase. The shared identity between the haloacid and haloalkane dehalogenases does not indicate relatedness between these two types of dehalogenases. The amino-terminal and carboxy-terminal homologies of mammalian soluble epoxide hydrolase to the respective dehalogenases suggests that this epoxide hydrolase, but not the soluble epoxide hydrolase of plant or the microsomal epoxide hydrolase, derives from a gene fusion. The homology of microsomal to soluble epoxide hydrolase suggests they derive from a gene duplication, probably of an ancestral bacterial (epoxide) hydrolase gene. Based on homology to haloalkane dehalogenase, the catalytic residues for the soluble and microsomal epoxide hydrolases are predicted. A nomenclature system based on divergent molecular evolution is proposed for these epoxide hydrolases.

Rate-dependent prolongation of action potential duration in single ventricular myocytes obtained from hearts of rats with streptozotocin-induced chronic diabetes sustained for 30-32 weeks

We examined the characteristics of the action potentials of single ventricular myocytes obtained from the hearts of rats with chronically-induced diabetes. Male Wistar rats were made diabetic by injecting streptozotocin (65 mg/kg) and 30-32 weeks later the hearts were excised and used for an electrophysiological study. Action potentials were recorded from isolated right ventricular myocytes by an electrode fabricated for patch clamp in the whole-cell recording configuration. The action potential durations (APDs) of steady state chronic diabetic rat myocytes were longer than those of age-matched normal rat myocytes at all levels of repolarization (APD25, APD50, APD75, and APD90). As the stimulation frequency was increased (0.2-2 Hz), the APDs were lengthened in both diabetic and normal rats, and the difference of APDs between the groups was greater when the stimulation frequency was higher. When we examined alterations of APDs under conditions of train stimulation (2Hz, 20 stimuli), (1) the APDs in both groups were prolonged, and (2) the degree of prolongation of APD was significantly greater and the rate of APD prolongation was significantly faster in myocytes from the diabetic rats. The prolongation of APD in these heart cells is probably secondary to alteration of the transient outward current Ito, and sheds light on repolarization abnormality in cases of diabetic cardiomyopathy.

Effects of KT-362, a new antiarrhythmic agent, on membrane ionic currents of guinea pig ventricular myocytes

We studied the effects of KT-362, (5-[3[2-(3,4-dimethoxyphenyl)ethyl]amino]-1-oxopropyl]-2,3,4,5- tetrahydro-1,5-benzothiazepine fumarate), a newly synthesized vasodilating and antiarrhythmic agent, on membrane currents of single guinea pig ventricular cells, using whole-cell voltage-clamp techniques. In the steady state with a stimulation frequency of 0.5 Hz, KT-362 at concentrations of 10 and 30 microM decreased the peak sodium current (INa) in a concentration-dependent manner, i.e., by 27% and 49%, respectively. The inhibition of INa by this agent was use-dependent: KT-362 (30 microM) inhibited INa by 21% at 0.2 Hz and by 51% at 1 Hz. In addition, KT-362 (10-30 microM) decreased the L-type Ca current (ICa) in a concentration-dependent fashion. The delayed rectifier potassium current and the inward rectifier potassium current were also inhibited by KT-362. The effects of KT-362 on INa and ICa were confirmed in experiments using ventricular papillary muscle preparations and microelectrode techniques. KT-362 (10-300 microM) decreased the maximum rate of rise of action potentials provoked at normal (2.7 mM) K+ concentration and that provoked at high (20 mM) K+ concentration. KT-362 at concentrations over 100 microM significantly depolarized the resting membrane, and the action potential duration remained unaltered. From these findings, we conclude that apart from the alleged inhibitory effects of this agent on the release of calcium from sarcoplasmic reticulum (it is therefore termed "an intracellular Ca++ blocker"), KT-362 suppresses a variety of membrane ionic currents of cardiac cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cibenzoline, a new class Ia antiarrhythmic drug, on various membrane ionic currents and action potentials of guinea-pig ventricular cells

We examined the effects of cibenzoline, a new class Ia antiarrhythmic drug, on various membrane ionic currents and action potentials of guinea-pig single ventricular cells, using patch clamp techniques in whole-cell configuration. Action potentials and the membrane currents were evoked at a clamping rate of 0.2 Hz, and all experiments were performed at 32-33 degrees C. 1) Cibenzoline (5, 10 and 30 microM) decreased the Na+ current (INa), in a concentration-dependent manner. The concentration of the half-maximal inhibition (Kd) for INa was estimated to be 7.8 microM. 2) In addition to the inhibition of INa, this drug (5, 10, and 30 microM) decreased, in a concentration-dependent manner, all other membrane currents examined, such as L-type Ca2+ current (ICa), delayed rectifier K+ current (IK), and inward rectifier K+ current (IK1). The Kd (apparent dissociation constant) values were 14.4 microM for ICa, 23.0 microM for IK, and 33.7 microM for IK1 respectively. 3) Cibenzoline (5, 10, and 30 microns) significantly shortened the action potential duration measured at both 30% and 90% repolarization without altering the resting membrane potential. From these findings, we conclude that apart from potent inhibitory effects on INa, cibenzoline possesses multiple blocking effects on other currents, e.g., ICa, IK and IK1, with a different potency (INa > ICa > IK > IK1) and with essentially the same efficacy. These effects may explain, at least in part, the alleged, potent antiarrhythmic effects of this drug.

Cloning of cDNAs for genes that are early-responsive to dehydration stress (ERDs) in Arabidopsis thaliana L.: identification of three ERDs as HSP cognate genes

In Arabidopsis thaliana L., accumulation of abscisic acid (ABA) began to increase 2 h after plants had been subjected to dehydration stress and reached maximum levels after 10 h. Differential hybridization was used to isolate 26 Arabidopsis cDNAs with gene expression induced by a 1 h dehydration treatment. The cDNA clones were classified into 16 groups based on Southern blot hybridization, and named ERD (early-responsive to dehydration) clones. Partial sequencing of the cDNA clones revealed that three ERDs were identical to those of HSP cognates (Athsp70-1, Athsp81-2, and ubiquitin extension protein). Dehydration stress strongly induced the expression of genes for the three ERDs, while application of ABA, which is known to act as a signal transmitter in dehydration-stressed plants, did not significantly affect the ERD gene expression. This result suggests that these HSP cognates are preferentially responsive to dehydration stress in A. thaliana, and that signaling pathways for the expression of these genes under conditions of dehydration stress are not mainly mediated by ABA. We also discuss the possible functions of these three ERD gene products against dehydration stress.

Characterization of an Arabidopsis cDNA for a soluble epoxide hydrolase gene that is inducible by auxin and water stress

A cDNA (1122 bp) was isolated from a cDNA library prepared from Arabidopsis thaliana L. that had been subjected to drought stress for 1 h. The sequencing of a genomic clone corresponding to the cDNA and S1 mapping analysis revealed that the cDNA lacked the first 6 bp from its translational start (ATG). The resulting open reading frame encodes a polypeptide of 321 amino acids, and the calculated molecular weight of this polypeptide is 36,423 Da. The deduced amino acid sequence shows a high degree of similarity to C terminal halves of those of soluble epoxide hydrolases (sEHs) of human, mouse and rat, 35.5%, 34.1% and 33.1%, respectively. The cDNA was expressed in Escherichia coli cells, and the expressed protein migrates at 40 kDa when analyzed by SDS-PAGE. The recombinant protein at 40 kDa is much smaller than the mammalian sEH (58 kDa) but has characteristics of activity and inhibition similar to the mammalian sEHs when assayed with the substrate trans-stilbene oxide and the inhibitors 4-fluorochalcone oxide (4FCO), (2R,3R)-3-(4-nitrophenyl) glycidol (RRNPG), and (2S,3S)-3-(4-nitrophenyl)glycidol (SSNPG), which indicates that the cDNA did encode a soluble epoxide hydrolase of A. thaliana (AtsEH). Drought stress, but not heat or cold stress, slightly increased the accumulation of the mRNAs for AtsEH. The level of AtsEH transcripts increased strongly after treatment with a plant hormone, auxin (2,4-dichlorophenoxyacetic acid, 2,4-D; naphthalene-acetic acid, NAA; and indole-3-acetic acid, IAA) in young, pre-bolting plants. Treatment with cytokinin (6-benzylaminopurine, BA), abscisic acid (ABA) or gibberellin (GA3) had no detectable effect on AtsEH transcript levels. The transcripts for AtsEH gene were detected in the aerial vegetative organs of bolting plants (i.e. stems and leaves), but not in roots, flowers and seeds. The possible function of AtsEH is discussed. A similar sEH cDNA has recently been characterized in potato (Stapleton et al., 1994).

Characterization of two cDNAs (ERD10 and ERD14) corresponding to genes that respond rapidly to dehydration stress in Arabidopsis thaliana

Two cDNA clones, designated ERD10 and EDR14, isolated from a cDNA library from one-hour-dehydrated plants of Arabidopsis thaliana L. were sequenced and characterized. The predicted ER10 and ERD14 polypeptides have a compositional bias towards Glu (19.62% and 21.08%, respectively) and Lys (16.15% and 18.38%, respectively) and both lack Trp and Cys residues. The amino acid sequences deduced from of both cDNAs are very similar to those of Group II LEA (late embryogenesis abundant) proteins, a class of proteins that accumulate late in embryogenesis and whose gene expression is induced by the plant hormone abscisic acid (ABA). Genomic Southern blot analysis suggested the existence of an ERD10-related gene. The expression of the genes that correspond to ERD10 and ERD14 was strongly induced in rosette plants of Arabidopsis within 1 h of dehydration and elevated levels of transcripts were detected during 24 h of dehydration. Northern blot analysis of the cold-induced expression of both the erd10 and erd14 genes revealed a two-step induction process. Early induction occurred within 1 h and secondary induction occurred 5 h after the beginning of cold stress. Application of ABA induced the expression of both genes, but application of 2,4-D, BA, ABA and GA3 did not affect the expression of these genes. In bolting plants, both ERD10 and ERD14 transcripts were detected in stems, cauline leaves, roots and flowers, but their levels decreased during seed formation and only low levels of the transcripts were detected in seeds at the late-mature stage.

Modification of cardiac sodium current by intracellular application of cAMP

We examined the effects of intracellular perfusion of cyclic adenosine monophosphate (cAMP) on the sodium current (INa) of guinea-pig ventricular myocytes, using the whole-cell clamp technique. INa was elicited by depolarizing voltage steps (-20 mV) from a variety of holding potentials (-120 to -50 mV), under conditions of 60 mM extracellular Na+ concentration ([Na+]o) and at the temperature of 24-26 degrees C. Intracellular perfusion of cAMP decreased the INa elicited from the holding potentials less negative than -90 mV. In the presence of 1 mM cAMP, for example, the peak INa elicited from -80 mV decreased from 6.0 +/- 2.0 nA to 4.0 +/- 2.2 nA (mean +/- SD, P < 0.02, n = 7) within 3-6 min. In the presence of extracellular 3-isobutyl-1-methylxanthine (IBMX, 20 microM), much lower concentrations of cAMP (0.2 mM) yielded a comparable effect. On the other hand, intracellular perfusion of cAMP increased the INa elicited from very negative holding potentials (< -100 mV). For instance, the application of cAMP (1 mM) increased the INa elicited by step depolarizations from -120 mV (to -20 mV), from 9.9 +/- 2.1 nA to 11.0 +/- 3.1 nA (P < 0.05, n = 5). The former effect was attributed to a marked shift of the steady-state inactivation curve of INa to the negative direction; the voltage of half-inactivation shifted from -77.9 +/- 1.0 to -83.5 +/- 1.4 mV, or by -5.6 mV. The latter effect may be explained by increases in maximum available conductance of INa.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of two cDNAs (ERD11 and ERD13) for dehydration-inducible genes that encode putative glutathione S-transferases in Arabidopsis thaliana L

Two cDNA clones, designated ERD11 and ERD13, isolated from a cDNA library from Arabidopsis thaliana L. plants dehydrated for 1 h were sequenced and characterized. These clones encoded polypeptides that were homologous to glutathione S-transferases of tobacco and maize. Genomic Southern hybridization suggested that there are a few additional genes showing high similarity to the ERD11 gene in the Arabidopsis genome. The expression of the genes for ERD11 and ERD13 was induced by dehydration, but was not affected by the application of four plant growth regulators, 2,4-dichlorophenoxyacetic acid 6-benzylaminopurine, abscisic acid, or gibberellic acid.

Characterization of cDNA for a dehydration-inducible gene that encodes a CLP A, B-like protein in Arabidopsis thaliana L

Sequence was obtained from a cDNA clone, designated ERD1, isolated from a cDNA library of 1-hour-dehydrated plants of Arabidopsis thaliana L. The clone (3150 bp) contains an open reading frame of 946 amino acid residues with greater than 34% sequence identity to the regulatory subunit of the Clp ATP-dependent protease in Escherichia coli and contains a putative chloroplast-targeting signal at the N-terminus. Southern blot analysis suggested the presence of additional ERD1-related genes in A. thaliana. The expression of ERD1 gene was strongly induced by dehydration-stress but not by heat-, cold-, or heavy-metal-stress. In addition ERD1 gene-expression was not strongly affected by treatment with plant growth regulators, such as auxin, cytokinin, abscisic acid, and gibberellic acid, or by starvation-stress for 10 hours.

Ionic mechanisms of action potential prolongation at low temperature in guinea-pig ventricular myocytes

1. We studied the effects of low temperature on the action potentials and membrane currents of guinea-pig ventricular myocytes, using a tight-seal whole-cell clamp technique. 2. The action potential duration at 95% repolarization was prolonged from 146 +/- 33 ms (mean +/- S.D., n = 6) at 33-34 degrees C (control temperature) to 314 +/- 83 ms at 24-25 degrees C (low temperature). 3. In whole-cell clamp experiments, low temperature decreased the calcium current (ICa), the delayed rectifier potassium current (IK), and the inwardly rectifying potassium current (IK1) with 'apparent' Q10 (temperature coefficient) values of 2.3 +/- 0.6 for ICa, 4.4 +/- 1.2 for IK tail current and 1.5 +/- 0.3 for IK1 (n = 7). 4. The effect of low temperature on IK was further studied in the presence of 0.6 microM nicardipine to block ICa. The decay phase of the IK tail consisted of two exponential components. The fast but not the slow component was highly sensitive to the temperature change with an apparent Q10 of 4.5. 5. We found that a component of time-independent current is also sensitive to the temperature. The current had a linear I-V relationship and remained almost unchanged after inhibition of Na(+) -K+ pump in K(+)-free external solution. 6. Using our mathematical model of the ventricular action potential (a modification from the DiFrancesco-Noble model), we simulated the action potential at low temperature by modifying some of the membrane currents, namely IK, IK1, ICa and a component of background current. It was shown that simultaneous changes in these currents could reproduce approximately 75% of the action prolongation induced by low temperature.

Differential mechanism of block of palmitoyl lysophosphatidylcholine and of palmitoylcarnitine on inward rectifier K+ channels of guinea-pig ventricular myocytes

We investigated the effect of lysophosphatidylcholine (lysoPtdCho) and palmitoylcarnitine (PamCar), ischemia-induced amphipathic lipid metabolites, on the inward rectifier K+ channel in guinea-pig ventricular cells, under whole-cell and cell-attached configurations with patch-clamp techniques. (a) Both lysoPtdCho (10-50 microM) and PamCar (10-50 microM) depolarized the resting membrane potential (RP), retarded the repolarization of action potential, provoked spontaneous action potential discharges from oscillatory afterpotentials, and eventually caused a sudden rise of the RP to plateau levels. (b) These lysoPtdCho- or PamCar-induced depolarizations of RP were due to a decrease in the inward rectifier K+ current (IK1), and the sudden rise of the RP could be accounted for by a crossover of N-shaped current-voltage relationship on the voltage axis (zero current line) more than once. (c) Single-channel studies in the cell-attached mode revealed that lysoPtdCho (5-100 microM) decreased the conductance of the single IK1 channel with little change in its open probability, whereas PamCar (10-50 microM) did so by decreasing the open probability, with the channel conductance unaltered. (d) A short-chain acylcarnitine, l-propionylcarnitine (PpCar, 100 microM), prevented the depressant effect of lysoPtdCho (50 microM), but not of PamCar (50 microM), on the IK1. (e) Both lysoPtdCho and PamCar produced identical electrophysiological alterations on the membrane potential and IK1 in whole-cell recordings. However, molecular mechanisms involved in the effects of these toxic metabolites on single IK1 channels differ.

A comparative study of effects of isoproterenol and dihydroouabain on calcium transients and contraction in cultured rat ventricular cells

We investigated the effects of isoproterenol, a beta-adrenergic agonist, and dihydroouabain, a Na+,K(+)-pump inhibitor, on Ca2+ transients and contraction of cultured rat ventricular cells and compared the effects with those of altered external ion concentrations, with special reference to the changes in diastolic intracellular free calcium concentration ([Ca2+]i). We measured [Ca2+]i of cultured cell aggregates, stimulated at 1.0 Hz, with the use of dual-wavelength microfluorometry of fura-2, at room temperature (24-26 degrees C). The contraction was measured as a shortening of the aggregates using a photodiode array placed on a video monitor. Isoproterenol increased the magnitude of contraction and the peak amplitude of the Ca2+ transient, in a concentration (10(-9)-10(-6) M)-dependent manner, but did not change the diastolic Ca2+ level. Isoproterenol at 10(-7) M or higher significantly shortened the duration of contraction and half decay time of a Ca2+ transient yet it did not change the time to peak. Dihydroouabain (10(-7)-10(-5) M) increased the contraction and elevated both systolic and diastolic calcium levels but it did not alter the duration of contraction, the time to peak and the half decay time. The effects of dihydroouabain on Ca2+ transients were mimicked by lowering [K+]o (0.4 mM), by lowering [Na+]o (74 mM) or by elevating [Ca2+]o (3.6 or 5.4 mM). Ryanodine (10(-5) M), by itself, decreased systolic Ca2+ transient amplitude, increased diastolic Ca2+ levels and prolonged the time to peak and the half decay time. In the presence of ryanodine, isoproterenol increased both systolic and diastolic [Ca2+]i. Thus, most procedures that increased the systolic Ca2+ transient amplitude increased the diastolic Ca2+ levels as well, and enhanced the contraction. The only exception was isoproterenol that markedly increased the systolic Ca2+ transient amplitude without affecting the diastolic Ca2+ level, a finding in keeping with the observation that isoproterenol stimulates Ca2+ uptake by the sarcoplasmic reticulum.

Background inward current in ventricular and atrial cells of the guinea-pig

Atrial and ventricular myocytes were exposed to Ca(2+)- and K(+)-free solutions containing blockers of gated channel and exchange currents. Replacement of external sodium by large organic cations revealed a background sodium current ib,Na. In atrial cells, the average conductance was 5.0 pS pF-1. In ventricular cells the conductance was 2.3 pS pF-1. Together with previous results, these figures reveal a strong gradient of background current density: sinus > atrium > ventricle. Replacement of sodium with inorganic cations showed that the channel selectivity behaves like an Eisenman group III/IV sequence, in agreement with previous results. The permeability of the channel to TMA was found to be pH dependent, suggesting that protonation of the channel is a factor determining permeation in addition to ionic size. The values of gb,Na obtained from these experiments are very similar to those assumed in computer modelling of cardiac cell electrical activity.

cDNA cloning of ECP40, an embryogenic-cell protein in carrot, and its expression during somatic and zygotic embryogenesis

A cDNA of 1.2 kb was isolated from a cDNA library of embryogenic cells of carrot (Daucus carota L.) by use of nucleotide sequences that encode two internal amino-acid sequences of ECP40 (an embryogenic-cell protein with a relative molecular mass of 40,000). A genomic Southern blot using the cDNA as probe suggested that there are at least two genes for ECP40 in the carrot genome. The cDNA encoded an open reading frame of 306 amino acids, and the deduced amino-acid sequence was found to share two motifs, namely SSSSSSEDDGXGGRRKKGXXXKIKEKLXGG and EKKXXXDKIKXKLPG, with rab16 protein from rice and dehydrins from barley and maize. The level of expression of these proteins has been reported to be high during late embryogenesis and to be induced by a plant hormone, ABA. Accumulation of ECP40-specific transcripts started 18 days after flowering and continued until maturation of seeds, but the levels decreased within 24 h after imbibition. ECP40 and its mRNAs were detected in the endosperm and zygotic embryos of mature seeds by immunohistochemistry and in situ hybridization. Exogenous application of 0.1 mM ABA to carrot seedlings did not induce expression of the gene for ECP40, while drought treatment induced the accumulation of low levels of the mRNAs. During somatic embryogenesis, the mRNAs were found at high levels in embryogenic cells and at low levels in somatic embryos at the torpedo stage. Immunohistochemical analysis and in situ hybridization showed that both ECP40 and its transcripts were preferentially localized in the peripheral cells of the clusters of embryogenic cells. In somatic embryos, application of ABA resulted in increases in levels of mRNAs for ECP40 up to the levels in embryogenic cells, but no such increases were observed in ABA-treated embryogenic cells. The pattern of expression of the gene for ECP40 during somatic embryogenesis was basically the same as that of ECP31, another ABA-regulable embryogenic-cell protein of carrot, the presence of which has been correlated with the embryogenic competence of cultured cells (T. Kiyosue, S. Satoh, H. Kamada and H. Harada, Plant Physiol 95 (1991) 1077-1083). The various results together imply that a group of ABA-inducible genes is expressed in these embryogenic cells.

Cibenzoline inhibits diazoxide- and 2,4-dinitrophenol-activated ATP-sensitive K+ channels in guinea-pig ventricular cells

1. We have investigated the effects of diazoxide (a sulphonamide derivative) and cibenzoline (a class I antiarrhythmic drug) on ATP-sensitive K+ currents in guinea-pig ventricular cells, using whole-cell clamp techniques. 2. Diazoxide (50 microM) produced a marked shortening of action potential duration which was antagonized by 1 microM glibenclamide, an ATP-sensitive K+ channel blocker. 3. Diazoxide (50 microM) increased the quasi-steady state outward current elicited by a ramp voltage protocol (-20 mV s-1) at potentials positive to about -70 mV. This effect was completely prevented in the presence of glibenclamide (1 microM), thereby suggesting that diazoxide opens ATP-sensitive K+ channels. 4. Cibenzoline (5 microM) depressed the diazoxide-induced increases in the outward current and the pretreatment with this agent prevented the development of the diazoxide-induced outward current. 5. Cibenzoline (10 microM) reversed the 2,4-dinitrophenol (50 microM)-induced shortening of the action potential duration partially but significantly. 6. These results suggest that diazoxide activates ATP-sensitive K+ channels of guinea-pig ventricular cells and that cibenzoline, at therapeutic concentrations, inhibits this channel.

Blockade of 2,4-dinitrophenol induced ATP sensitive potassium current in guinea pig ventricular myocytes by class I antiarrhythmic drugs

OBJECTIVE

The aim was to assess the effects of various antiarrhythmic drugs on 2,4-dinitrophenol (DNP) induced outward current (IDNP), presumably the ATP sensitive K+ current (IK,ATP) of isolated cardiac cells and to discuss mechanisms involved in the hypoglycaemia which occurs in patients on these drugs.

METHODS

The quasi-steady state current-voltage relationship from the isolated guinea pig ventricular cells was measured using whole cell voltage clamp techniques with a ramp pulse programme. The effects of seven different antiarrhythmic drugs on IDNP were examined. Action potentials were elicited at a rate of 0.2 Hz by an intracellular current injection.

RESULTS

DNP (50 mumol.litre-1) increased the quasi-steady state outward current at potentials positive to about -60 mV. This current (IDNP) was completely inhibited by the subsequent application of glibenclamide (1 mumol.litre-1), thereby suggesting that the IDNP is probably IK,ATP. Cibenzoline (10 mumol.litre-1, class Ia), disopyramide (30 mumol.litre-1, class Ia), and procainamide (100 mumol.litre-1, class Ia) significantly inhibited the IDNP by 95.5(SD 11.3)%, 77.8(21.2)%, and 76.4(23.9)% respectively. Flecainide (class 1c) inhibited the IDNP by 66.9(23.9)% at 10 mumol.litre-1 but not at 2 mumol.litre-1. Mexiletine (30 mumol.litre-1, class Ib), pilsicainide (50 mumol.litre-1, class Ic), and E4031 (10 mumol.litre-1, class III) at concentrations as high as approximately fivefold the clinically effective blood levels, did not suppress IDNP. Except for 10 mumol.litre-1 flecainide, all the concentrations listed above which blocked IDNP were within twofold of the clinical blood concentrations documented to be effective for suppression of arrhythmias. Cibenzoline, disopyramide, and procainamide, but not flecainide, belong to class Ia antiarrhythmic drugs. All these class Ia antiarrhythmic drugs "shortened" the action potential duration of guinea pig ventricular cells, an opposite change to that noted for multicellular preparations, eg, guinea pig papillary muscles.

CONCLUSIONS

Class Ia antiarrhythmic drugs (cibenzoline, disopyramide, and procainamide) inhibit IDNP (presumably IK,ATP) in guinea pig ventricular cells within a range of therapeutic concentrations. This inhibitory effect of IK,ATP can probably explain the hypoglycaemia which occurs in some patients receiving these drugs, and the prolongation of the action potential duration alleged to occur in "superfused" papillary muscles.

Partial amino-acid sequence of ECP31, a carrot embryogenic-cell protein, and enhancement of its accumulation by abscisic acid in somatic embryos

ECP31, an embryogenic-cell protein from carrot (Daucus carota L.), was purified by sequential column-chromatographic steps and digested by V8 protease on a nitrocellulose membrane. The resultant peptides were separated by reverse-phased column chromatography and sequenced. The sequences obtained were 70-80% homologous to those of a late-embryogenesis-abundant protein (D34) from cotton (Baker et al, 1988, Plant Mol. Biol. 11, 227-291). The level of ECP31 in somatic embryos of carrot was increased by treatment of the embryos with 3.7 · 10(-6) M abscisic acid (ABA) for 48 h, and there was no change in this enhanced level for up to 192 h in the presence of ABA. No similar enhancing effect of ABA was observed on the level of ECP31 in embryogenic callus or segments of carrot hypocotyls. In an immunohistochemical analysis, ECP31 was found in epidermal tissue and in the vascular system of ABA-treated somatic embryos.

Inhibitory effects of palmitoylcarnitine and lysophosphatidylcholine on the sodium current of cardiac ventricular cells

We investigated the effects of ischemia-related amphipathic compounds, palmitoylcarnitine (PamCar, 0.5-50 microM) and lysophosphatidylcholine (lysoPtdCho, 5-50 microM) on sodium current (INa) of guinea-pig ventricular myocytes. The cells were perfused with low-Na+ (60 mM) Tyrode's solution, and Ca2+ and K+ currents were blocked by external Co2+ (3 mM) and internal Cs+ (140 mM), respectively. INa was elicited by depolarizing voltage steps from a holding potential of -100 mV at a temperature of 33 degrees C. PamCar (5 microM) decreased the peak INa (attained at -20 mV or -30 mV) from 6.1 +/- 2.1 nA to 3.9 +/- 1.4 nA (n = 11), or by 36.1% within 2 min, and shifted the curve of steady-state INa inactivation by 5.4 mV in the positive direction (from -76.3 +/- 4.6 mV, control to -70.9 +/- 4.0 mV, in PamCar, n = 4). Partial restoration of the amplitude and the shift of the steady-state inactivation curve of INa was attained after washout of PamCar. In contrast, lysoPtdCho at concentrations over 10 microM irreversibly depressed the INa within 0.5-3 min and the reduction of INa was followed by cell contracture or cell death (n = 9). The survival time, defined as a period from the start of lysoPtdCho application to the time of the last successful recording of the INa (before evolution of sudden changes in the holding current), depended on the concentrations of lysoPtdCho. Both PamCar and lysoPtdCho retarded the time course of activation and inactivation of INa.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and immunohistochemical detection of an embryogenic cell protein in carrot

An embryogenic cell protein from carrot (Daucus carota L.), designated ECP31 for embryogenic cell protein and with a relative mass of 31,000, was purified by sequential column chromatographies. Its apparent relative mass was estimated to be 120,000 by gel filtration. Immunoblotting and immunohistochemical studies showed that ECP31 was preferentially localized in the peripheral cells of clusters of embryogenic cells in the presence of 2,4-dichlorophenoxyacetic acid (2,4-D) and disappeared during the course of somatic embryogenesis in the absence of 2,4-D. ECP31 began to accumulate on the 33rd day after initiation of cultures of hypocotyl segments on Murashige-Skoog medium with 2,4-D, when callus began to appear on the segments. In dry seeds, lower amounts of ECP31 were located throughout the entire zygotic embryos but not in endosperm. ECP31 was also detected in provascular tissue of malformed somatic embryos.

Induction of somatic embryogenesis in carrot by heavy metal ions

A new method for the induction of somatic embryos has been demonstrated. Somatic embryos were formed without a visible interventing callus stage when apical tips from 1-week-old seedlings of carrot (Daucus carota cv. US-Harumakigosun) were cultured for 1–3 weeks on Murashige and Skoog's medium without growth regulators but containing heavy metal chlorides, such as CoCl2, NiCl2, ZnCl2, and CdCl2, and then transferred to Murashige and Skoog's medium. These results suggest that the stresses caused by these chemicals trigger the induction of somatic embryogenesis in carrot. Key words: Daucus carota, somatic embryo, stress, tissue culture.

Two pyridine analogues with more effective ability to reverse multidrug resistance and with lower calcium channel blocking activity than their dihydropyridine counterparts

Four pyridine analogues and their dihydropyridine counterparts were examined for their ability to reverse drug resistance in a multidrug-resistant human carcinoma cell line, KB-C2. Two pyridine analogues were more able to reverse drug resistance than their dihydropyridine counterparts. The other two pyridine analogues had an effect on drug resistance similar to their dihydropyridine counterparts. The calcium channel-blocking activity of all the pyridine analogues was considerably lower than that of the dihydropyridine analogues. Of the pyridine analogues, 2-[4-(diphenylmethyl)-1-piperazinyl]ethyl 5-(trans-4,6-dimethyl-1,3,2-dioxaphosphorinan-2-yl)-2,6-dimethyl-4 -(3- nitrophenyl)-3-pyridinecarboxylate P-oxide (PAK-104P) was the most effective in reversing multidrug resistance. PAK-104P (1 and 5 microM) completely reversed the drug resistance in KB-8-5 and KB-C2 cells, respectively. The reversing effect of PAK-104P was greater than that of other multidrug resistance-reversing agents, cepharanthine, verapamil, nimodipine, and nicardipine. PAK-104P at 1 microM increased about 10-fold the accumulation of vinblastine in KB-C2 cells, whereas verapamil at the same concentration increased the accumulation about 2-fold. The inhibition of [3H]azidopine photolabeling of P-glycoprotein by the pyridine and dihydropyridine analogues except 2-[methyl(phenyl-methyl)amino]ethyl 4-(2-chlorophenyl)-5-(4-methyl-1,3,2-dioxaphosphorinan-2-yl)-1,4-d ihydro-2,6- dimethyl-3-pyridinecarboxylate P-oxide correlated with the reversing of drug resistance by the analogues. Some newly synthesized pyridine analogues seemed to have lower calcium channel-blocking activity and more potent resistance-reversing ability than verapamil and other calcium channel blockers.

[Variations of dentition in raccoon dogs (Nyctereutes Procynoides Viverrinus T.) Anomalies in number of the teeth]

A study on the number of anomalous teeth was made by using gross and radiographic examinations on 179 skulls (male: 68, female: 53, unknown: 58) of raccoon dogs (Nyctereutes Procynoides Viverrinus T.) captured in the northern part of Kyushu. Results were as follows: 1. 8 skulls had 15 supernumerary teeth. They were in the upper incisor, the upper third premolar and the upper and lower first premolar regions. 2. 35 skulls had 58 congenitally missing teeth. Most of them were upper and lower first premolars or lower third molars. 3. One skull had one supernumerary tooth in the upper second incisor region and one congenitally missing tooth, a lower third molar. 4. The anomalous teeth were about 25%, the supernumerary teeth and congenitally missing teeth were about 4.5% and 20% respectively.

Isoproterenol, DBcAMP, and forskolin inhibit cardiac sodium current

We studied the effects of isoproterenol (ISP), dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP), and forskolin on the sodium current (INa) of guinea pig ventricular myocytes using the tight-seal, whole cell voltage-clamp method. The extracellular [Na+] [( Na+]o) was decreased to 60 mM by replacing NaCl with sucrose (temperature, 32-33 degrees C). Ionic currents other than Na+ were suppressed using appropriate channel blockers. Depolarizing clamp pulse (duration, 30 ms) was applied at a rate of 0.2 Hz from a holding potential of -80 mV. ISP (1 microM) decreased the peak INa by 34% from 6.1 +/- 1.9 (SD) nA (control) to 4.0 +/- 1.5 nA (n = 7). The inhibition was more prominent at less negative potentials and disappeared in the presence of a beta-blocker (10 microM atenolol). The effects of DBcAMP (1-5 mM) and forskolin (3 microM) mimicked those of ISP and depressed the peak INa reversibly. DBcAMP (5 mM) shifted the inactivation curve of INa [h infinity-membrane potential (Em) relationship] to a hyperpolarizing direction, by 3.4 +/- 0.8 mV (n = 5). These findings suggest that ISP inhibits the cardiac INa+, probably by altering the gating mechanism of the Na+ channel, and that the effect is secondary to the increased levels of intracellular cAMP, with possible acceleration of cAMP-dependent phosphorylation of the channel.

Glucose reverses 2,4-dinitrophenol induced changes in action potentials and membrane currents of guinea pig ventricular cells via enhanced glycolysis

The precise mechanism involved in the restoration by glucose of action potentials and membrane currents has not been established, so we studied it in single guinea pig ventricular cells under conditions of metabolic inhibition by 2,4-dinitrophenol (DNP). Application of DNP (50 mumol.litre-1) significantly shortened the action potential duration (APD) from 276.3 (SD 47.5) to 43.0(3.9) ms (n = 10). The increase in glucose concentration from 5.5 (control) to 22 mmol.litre-1 significantly restored the APD within 10 min, to 233.2(51.2) ms. In tight seal whole cell clamp studies, we found that DNP increased the steady state outward currents at potentials positive to -60 mV, and that this current was all but suppressed by 22 mmol.litre-1 glucose. The glucose induced recovery in the APD and membrane current was not seen in the presence of 2-deoxyglucose (2 mmol.litre-1), an inhibitor of glycolysis. Insulin (40 mIU.ml-1) reversed the DNP induced shortening of APD and abolished the increase in the outward current in the presence of 11 mmol.litre-1 glucose, though the application of glucose alone at this concentration failed to reverse these changes. Glucose (5.5 to 44 mmol.litre-1) did not directly affect single channel currents of ATP regulated K channels of the excised patch membrane in an outside out mode. These results suggest that the antagonising effects of glucose on the DNP induced alterations in APD and membrane currents are mediated by an increase in intracellular ATP concentration via enhanced glycolysis. Insulin might enhance this effect by facilitating the transport of glucose across the cell membrane.

Late sodium current and its contribution to action potential configuration in guinea pig ventricular myocytes

We used the patch clamp technique to study the nature of the late sodium current in guinea pig ventricular myocytes. In a cell attached mode of single channel recording at room temperature (22-24 degrees C) two kinds of late (100 msec or more after beginning of the depolarizing pulse) sodium channel activities were recognized. One is isolated brief openings appearing once for about 120 depolarizations per channel (background type), while the other type is sustained openings with rapid interruptions (burst type) that occurred only once for 2,700 depolarizations per channel. The time constant obtained from the open time histogram of the burst type (1.05 msec) was about five times longer than that of background type (0.18 msec, measured at the potential 10 mV above the threshold). Magnitude of the late sodium current flowing through the entire surface of a myocyte was estimated with tetrodotoxin (60 microM), a specific inhibitor of sodium channels, in whole-cell clamp experiments. The steady tetrodotoxin-sensitive current of 12 to 50 pA was registered at -40 mV (26 +/- 14 pA, mean +/- SD, n = 5), in good agreement with the late sodium current calculated from the single channel recording. Tetrodotoxin produced small (congruent to 10%) but significant decreases in the action potential duration. These results suggest the presence of a small but significant late sodium current with slow inactivation kinetics and that this current probably plays a significant role in maintaining the action potential plateau and the duration in guinea pig ventricular myocytes.

[Frequency of three-rooted mandibular first molars. Survey by x-ray photographs]

The frequency of three rooted mandibular first molars was surveyed. Subjects were of 1,353 male and female students trained in radiology at Fukuoka Dental College whose average age was 24.3 years old. Dental (complete radiographic survey using 14 films) and panoramic radiographs of their mandibular first molars were taken during a period of 9 years from 1978 to 1986. The results were as follows: 1) The number of the three-rooted mandibular first molars was 440 (18.8%) of 2,331 teeth, including 240 (20.6%) of 1,163 in the right side and 200 (17.1%) of 1,168 in the left. 2) 274 (11.8%) of the three-rooted mandibular first molars were identified by radiographs of the premolar region, 42 (1.8%) by radiographs of the molar region, 124 (5.3%) by radiographs of both the premolar and the molar region. 3) Panoramic radiography identified 70 (15.9%) out of 440 three-rooted mandibular first molars. 4) 136 (12.7%) of 1,070 subjects who had bilateral mandibular first molars had three-roots on both sides 127 (11.9%) of 1,070 had them on one side.

Effects of AN-132, a novel antiarrhythmic lidocaine analogue, and of lidocaine on membrane ionic currents of guinea-pig ventricular myocytes

We studied the effects of AN-132 (10, 30 and 100 mumol/l), an analogue of lidocaine, on membrane currents and action potentials of single guinea-pig ventricular cells using whole-cell clamp techniques. The effects of lidocaine, an authentic class I antiarrhythmic agent were used for comparative purposes. (1) AN-132 decreased the Na current (INa) in a concentration-dependent manner, with a greater efficacy than seen with lidocaine. The concentration of the half maximal inhibition on INa (Kd) was 31.7 mumol/l for AN-132 and 94.9 mumol/l for lidocaine. (2) AN-132 also decreased the Ca current (ICa), concentration-dependently, while lidocaine had only a minor effect on ICa. The half maximal inhibition on ICa (Kd) was 23.1 mumol/l and 27.4 mumol/l for AN-132 and lidocaine, respectively. (3) AN-132 decreased the IK1, in a concentration-dependent manner; lidocaine was without effect. (4) AN-132 increased the unspecified steady state outward current, at positive potentials and depressed the time- and voltage-dependent outward K current (IK). Lidocaine had no effect on either current. (5) AN-132 shortened the action potential duration (APD), in a concentration-dependent manner, without altering the resting potential. From these findings, we conclude that apart from a potent inhibitory effect on INa, AN-132 had a variety of effects on other currents, properties not shared by lidocaine. Such multiple blocking effects on the membrane currents may relate to the alleged potent antiarrhythmic effect of AN-132.

Effects of trimetazidine on action potentials and membrane currents of guinea-pig ventricular myocytes

The effects of trimetazidine on membrane potentials and membrane currents of enzymatically isolated guinea-pig ventricular cells were studied with the use of giga-seal suction pipettes for patch clamp. Trimetazidine (3 X 10(-5) M) decreased the action potential duration from 433 +/- 179 ms (mean and S.D., n = 9) to 319 +/- 156 ms within 8 mins. In voltage clamp experiment, trimetazidine at a concentration of 1.5 X 10(-4) M decreased the peak amplitude of calcium current by 40% (0.92 +/- 0.46 nA to 0.55 +/- 0.19 nA, mean +/- S.D., n = 5). The effect on calcium current was rate-dependent, e.g., at 1 Hz, trimetazidine blocked a larger fraction of the calcium current than at 0.2 Hz. The drug decreased the conductance of potassium current which flows via inward rectifier potassium channel from 28 +/- 11 nS to 19 +/- 10 nS, n = 5, P less than 0.05). Trimetazidine shifted the steady state current-voltage relationship outward at potentials positive to -20 mV. This shift was not due to the enhanced time- and voltage-dependent outward current (Ik). From these findings, it was concluded that trimetazidine shortens action potential duration by blocking the calcium channels with increases in steady state outward current or a possible blockade of non-inactivated component of the calcium current, at the plateau potentials. The reduction of calcium current and of inward rectifier potassium current may protect the cardiac cells from accumulation of calcium ions and from loss of potassium ions, in the presence of ischemia.

Na,K-ATPase activity and repolarization of ventricular action potentials in simian hearts

We measured Na,K-ATPase activity and ATP content of 4 different areas of the left ventricular muscle of Japanese monkeys (Mucaca fuscata): The apex, base, and epicardium (Epi) and endocardium (Endo) of the free wall. We compared those values with electrical parameters such as action potential duration (APD) and the level of resing potentials. APDs of base and Endo were significantly longer than those of apex and Epi, respectively. There was no significant difference in ATP contents among the four tissues while Na,K-ATPase activity in Epi was significantly higher, thereby indicating that the maximum capacity of the Na,K-pump activity is greater in Epi than in Endo. This observation serves to explain the following differences in electrophysiology characteristics found between Epi and Endo: greater shortening of APD in Endo when the cycle length of stimulation was shortened (from 2,000 to 200 ms) or when ouabain (0.5-1 microM) was applied; larger amplitude of post-overdrive hyperpolarization in Epi; and marked ouabain-induced depolarization of the resting potential in Endo, as compared to Epi. We conclude that the difference in Na,K-ATPase activity accounts for the different electrical behavior observed in Epi and Endo of the simian ventricle.

Comparison of the inhibitory effects of mexiletine and lidocaine on the calcium current of single ventricular cells

Effects of mexiletine and lidocaine on inward calcium current (ICa) of single ventricular myocytes from guinea pigs were studied using tight seal whole cell clamp method. Mexiletine at the concentrations of 10, 30 and 100 microM decreased ICa by 23.0, 28.9 and 55.4%, respectively, while lidocaine decreased it by 8.9, 16.8 and 25.2%. At all concentrations tested, a potency for ICa inhibition in mexiletine was significantly greater than that in lidocaine (p less than 0.05). The results suggest that mexiletine has, at therapeutic concentrations, a considerable blocking action on the Ca channels other than well-known action on the Na channels.

Overcoming drug resistance in cancer cells with synthetic isoprenoids

A cultured subline (P388/ADM) of mouse P388 leukemia resistant to doxorubicin, vinblastine, vincristine, dactinomycin, and daunorubicin became sensitive again when treated with noncytotoxic doses of either of two synthetic isoprenoids: N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine) and N-(p-methylbenzyl)decaprenylamine X HCI (PMB-decaprenylamine). The isoprenoids also reversed resistance to doxorubicin and vincristine in a cultured vincristine-resistant P388 leukemia subline (P388/VCR). Median lethal doses (LD50) for PMB-decaprenylamine and SDB-ethylenediamine administered ip were 123 and 350 mg/kg against mice, whereas the LD50 for verapamil, another modifier of cellular drug resistance, was about 7.6 mg/kg. In vivo experiments with P388/VCR-bearing mice showed that both SDB-ethylenediamine and verapamil overcame vincristine resistance, but PMB-decaprenylamine showed only slight activity. SDB-ethylenediamine was especially effective, overcoming the vincristine resistance at 1 mg drug/kg. Since the structure of SDB-ethylenediamine resembles that of verapamil, a calcium-blocking agent that overcomes drug resistance, it was checked for calcium-blocking activity. However, calcium channel-blocking activity was not observed with 20 micrograms isoprenoid/ml, whereas calcium channel activity was completely blocked by 1 microgram verapamil/ml.

Antiarrhythmic effects of nicorandil on canine cardiac Purkinje fibers

Antiarrhythmic efficacy of nicorandil (SG-75) (1-100 microM), a coronary vasodilator, was investigated electrophysiologically with regard to the action potentials of canine Purkinje fibers. The main results obtained are as follows: (a) nicorandil suppressed three kinds of automaticities, i.e., spontaneous or low-K+-induced automaticity and electrical depolarization-induced automaticity; (b) the drug increased the effective refractory period relative to action potential duration and decreased differences between action potential duration and effective refractory period; and (c) in the presence of nicorandil (50 microM), membrane potentials at which the earliest premature response could be elicited were significantly more negative than control, thus leading to a much faster upstroke velocity of the premature response. These changes in electrophysiological properties suggest that the drug may be effective for treating selected cardiac arrhythmias due to both enhanced automaticity and reentry, particularly in the presence of a decreased membrane K conductance. These effects of nicorandil could be mostly attributed to an increase in membrane K conductance.

Lysophosphatidylcholine decreases single channel conductance of inward rectifier K channel in mammalian ventricular myocytes

Effect of lysophosphatidylcholine (LPC) on the inward rectifier K channel of the isolated guinea pig ventricular cell was studied using patch clamp technique. In that LPC (100 microM) decreased the magnitude of the single channel conductance from 48 +/- 5 pS (mean and S.D., n = 5) to 12 +/- 9 pS (n = 8), this event may be the prime factor related to the alleged LPC-induced depolarization of cardiac tissues.

Electrocardiogram and His bundle electrogram of Japanese monkeys (Macaca fuscata)

Electrocardiogram (ECG) was taken from Macaca fuscata in the supine position under secobarbital anesthesia. The ECGs were recorded in the leads of standard (I, II, III), augmented unipolar limb (aVR, aVL, aVF) and unipolar chest (V4R, V1, V2, V3, V4, V5, V6,). The ECG was similar to that of humans as well as the monkeys of other species in their general patterns and the voltage of each wave (P, Q, R, S, T), though the heart rate was considerably different. The direction of T wave was consistent with that of human ECG. The PR, QRS and QT intervals and the duration of P wave were in good agreement with those of monkeys of other species, and amounted to about 50% of those of human ECG. His bundle electrogram (HBE) was recorded with a tripolar electrode catheter inserted into the right ventricle via the femoral vein, and PA, AH, HV and PV intervals were measured. All of the values were also approximately 50% and PV intervals were measured. All of the values were also approximately 50% of those reported in human HBE. Such short time intervals observed in Macaca fuscata may be due to a smaller heart size of the monkey as compared to the human's. The measurements of ECG and HBE reported in the present study may be used as a normal reference in ECG and HBE of Macaca fuscata under anesthesia. The study suggests that the Macaca fuscata is useful as an animal model to investigate the repolarization process of human ECG.

Nature of "residual fast channel" dependent action potentials and slow conduction in guinea pig ventricular muscle and its modification by isoproterenol

The nature of "residual fast channel" dependent action potentials and conduction was studied in guinea pig ventricular papillary muscle in which the resting potential was reduced to 58 +/- 1 mV in high K+ (16.7 mM) Tyrode's solution, with or without isoproterenol (0.1 microM). In the absence of isoproterenol, the action potential had a slur on the upstroke and the maximum rate of rise (Vmax) was composed of 2 separable peaks: the early large (32 +/- 7 V/s, Vmax,fast) and the late small (10 +/- 2 V/s, Vmax,slow) ones. The conduction velocity ranged from 30 to 35 cm/s. The Vmax,fast was selectively depressed by l-verapamil (1 microgram/ml), indicating that the impulses were transmitted through incompletely inactivated ("residual") fast channels. Lidocaine (2 micrograms/ml) depressed Vmax,fast with reduction of conduction velocity to about 20 cm/s just before the conduction block. Isoproterenol quadrupled the Vmax,slow but decreased Vmax,fast. As a result, the Vmax,slow overrode the Vmax,fast without change in the conduction velocity. In the absence of isoproterenol, there was no rate-dependent change in the action potential duration and the effective refractory period among the rates of 0.1, 0.5, and 0.9 Hz. Isoproterenol produced rate-dependent shortening in action potential duration with rate-independent shortening of postexcitation refractoriness, thereby resulting in a significant shortening in the effective refractory period at faster rates (0.5 and 0.9 Hz). Results suggest that the "residual fast channel" could produce "slow conduction" and that the ionic channels (fast or slow) responsible for the slow conduction may alternate according to local concentrations of tissue catecholamines.

Effects of SG-75 (nicorandil) on electrical activity of canine cardiac Purkinje fibers: possible increase in potassium conductance

The effects of various concentrations (1-1000 microM) of SG-75 nitrate or nicorandil) were investigated in action potentials of canine Purkinje fibers with microelectrodes. In normal fibers stimulated at the standard cycle length of 1500 msec, the drug (1-100 microM) produced dose-dependent shortening in action potential duration without changes in the resting potential, the maximum rate of rise of phase 0 and the slope of phase 4 depolarization. The drug-induced percentage of shortening in the action potential duration was more pronounced at lower rates of stimulation and lower external K+ concentrations, but the shortening was unchanged in lower external Na+ concentrations. Depolarizations produced by Ba++ (0.04 mM) and low K+ (less than or equal to 1.35 mM) solution were partially reversed by the drug, whereas there were no effects on the high K+ (5.4-24.7 mM)-induced depolarizations. Stretch-induced depolarization was also partially recovered in the presence of the drug. SG-75 shortened the duration of the slow response produced by isoproterenol (1 microM) in the presence of 24.7 mM K+, with little change in the maximum rate of rise. We concluded that SG-75 increases membrane K+ conductance in cardiac Purkinje fibers probably by modifying ix1 and iK1 channels without changing the slow inward currents and that the effects are not mediated by muscarinic receptors. The computed action potentials indicated that this view was reasonable.

Na, K-ATPase activity, ATP and Pi concentrations in various regions of monkey heart and their relation to post-overdrive hyperpolarization

The relationship among Na, K-ATPase activity, ATP and inorganic phosphate (Pi) concentrations in functionally different regions of cardiac and skeletal muscles were studied in the Japanese monkey (Macaca fuscata). The activity of Na, K-ATPase was determined by the method of FIske and SubbaRow, and the concentrations of ATP and Pi, by isotachophoresis. The ATP concentrations in several regions of cardiac and skeletal muscles correlated positively with the Na, K-ATPase activities and Pi concentrations, whereas there was no significant correlation between the Na, K-ATPase activities and the Pi concentrations. Therefore, the ATP concentrations in functionally different regions of the tissues seemed to be a feasible measure of Pi concentrations and the Na, K-ATPase activities. The Na, K-ATPase activity was significantly higher in the epicardium than in the endocardium of the ventricle. The post-overdrive hyperpolarization was compared in these two tissues, using microelectrode methods. The hyperpolarization which followed overdrive stimulation (3.3-3.8 Hz) in the epicardium exceeded that in the endocardium, and was attributed to the difference in Na, K-ATPase activity. Our findings suggest that tissues with a higher Na, K-ATPase activity may have a more potent Na, K-pump activity, in association with higher tissue concentrations of ATP and Pi.

Modification of "depressed fast channel dependent slow conduction" by lidocaine and verapamil in the presence or absence of catecholamines--evidence for alteration of preferential ionic channels for slow conduction

We studied, with microelectrodes, the effect of lidocaine and 1-verapamil on the upstroke phase of action potentials and conduction velocity in incompletely depolarized ventricular papillary muscle (resting potential, -58 +/- 1 mV) perfused in a high K+ (16.7 mM) Tyrode's solution. The action potential upstroke had a slur and the maximum rate of rise (Vmax) consisted of 2 components: the first large (32 +/- 7 V/sec; Vmax,fast) and the second small (10 +/- 2 V/sec, Vmax,slow). The conduction velocity was slow and ranged about 30-35 cm/sec. Isoproterenol and noradrenaline increased Vmax,slow and decreased Vmax,fast, in a concentration dependent manner (10(-8) - 10(-5)M). These effects were abolished by following application of a beta-blocker, pindolol (1 microgram/ml). Thus, the dominant ionic channel responsible for the slow conduction seemed to alter from the depressed fast channel to the slow channel as the catecholamine concentration was increased. In the absence of isoproterenol, lidocaine (2 micrograms/ml) depressed Vmax with a resultant decrease of conduction velocity to 16.4 +/- 4.2 cm/sec and which was followed by a conduction block, while 1-verapamil was without effect. In the presence of isoproterenol (5 x 10(-7) M), 1-verapamil (1 microgram/ml) depressed the Vmax and decreased the conduction velocity to 16.9 +/- 4.2 cm/sec, just before development of the conduction block, while lidocaine was without effect. These results suggest that the dominant ionic channel responsible for the slow conduction in high K media (16.7 mM), can be readily altered by changes in extracellular catecholamine concentrations and that the slowest possible conduction velocity was approximately the same (about 16 cm/sec) between the depressed fast channel-dependent and the slow channel-dependent conductions. Clinical implications of these findings were discussed.

Single channel analysis of the inward rectifier K current in the rabbit ventricular cells

The inward rectifier K channel in rabbit ventricular cells was studied by the patch-clamp method. Single channel currents were recorded in giga-sealed cell-attached patches with 150 mM K+ in the pipette. The slope conductance in the membrane potential range from -140 to -40 mV was 46.6 +/- 6.7 pS (mean +/- S.D., n = 16), and was reduced by decreasing [K+] in the pipette (20 or 50 mM). The channel was blocked by an application of Cs+ or Ba2+ (0.04-1 mM) in the pipette. Outwardly directed current, recorded with 50 mM K+ in the pipette, revealed the inward rectification of the single channel current. The probability of the channel being open was 0.33 +/- 0.05 (n = 10) at the resting potential (RP=-81.7 +/- 1.7 mV, n = 16) with 150 mM K+ in the pipette, and it decreased with hyperpolarization. The mean open time of the channel was 178 +/- 25 msec (n = 6) at RP. The closed time of the channel seemed to have two exponential components, with time constants of 11.0 +/- 2.0 msec and 1.92 +/- 0.52 sec (n = 6) at RP. The slower time constant was increased with hyperpolarization. The averaged patch current recorded upon hyperpolarizing pulses demonstrated a time-dependent current decay as expected from the single channel kinetics. The results indicated that the inward rectifier K+ current has time- and voltage-dependent kinetics.

Electrophysiological and inotropic effects of Coenzyme Q10 on guinea pig ventricular muscle depolarized by potassium under hypoxia

The electrophysiological and inotropic effects of Coenzyme Q10 (CoQ10) on isoproterenol or barium-induced slow responses in ventricular papillary muscle, depolarized by high K+ concentration (21.6 mM) under hypoxia (PO2 = 40 mmHg), were studied with microelectrode techniques. For the isoproterenol-induced slow response, application of CoQ10 (50 micrograms/ml), which was emulsified with the aid of a special solvent, increased the maximum rate of rise of action potentials (Vmax), an indicator of the slow inward current, by about 40%, with no consistent effect on the action potential duration and developed tension. Application of the solvent alone produced a significant decrease in both Vmax and developed tension. However, in these solvent-pretreated preparations, CoQ10 produced a significant (by about 50%) recovery in both Vmax and developed tension. The action potential duration was not changed by either the solvent alone or the application of CoQ10. The developed tension of the slow response consisted of early and late components. CoQ10 produced significantly more recovery in the late component than in the early one, suggesting that the recovery effect was due to increased slow inward Ca2+ current. CoQ10 did not reverse any parameter in the slow response induced by BaCl2 (0.2 mM). The results suggest that CoQ10 has significant but limited reversing effects on the hypoxia-induced deterioration of the slow response, and that the recovery is presumably due to increased availability of slow channels via increased production of ATP.