Enhanced anxiety-like behavior induced by chronic neuropathic pain and related parvalbumin-positive neurons in male rats

Anxiety commonly co-occurs with and exacerbates pain, but the interaction between pain progression and anxiety, and its underlying mechanisms remain unclear. Inhibitory interneurons play a crucial role in maintaining normal central nervous system function and are suggested to be involved in pain-induced anxiety. This study aimed to elucidate the time-dependent effects of neuropathic pain on the developmental anxiety-like behaviors and related inhibitory interneurons; parvalbumin (PV)- and cholecystokinin (CCK)-positive neurons in corticolimbic regions. Using an 8-week-old male Wistar rat model with partial sciatic nerve ligation (pSNL), anxiety-like behaviors were biweekly assessed post-surgery through open field (OF) and elevated plus maze (EPM) tests. From 4 weeks post-surgery, pSNL rats exhibited reduced OF center time, rearing, and initial activity, along with diminished EPM open-arm activities (time spent, head dips, movement, and rearing), which correlated with the paw withdrawal threshold. These effects were absent at 2 weeks post-surgery. At 8 weeks post-surgery, specific behaviors (decreased total rearing and increased inactive time in EPM) were observed in the pSNL group. Immunohistochemistry revealed changes in PV- and CCK-positive neurons in specific corticolimbic subregions of pSNL rats at 8 weeks post-surgery. Notably, PV-positive neuron densities in the basolateral amygdaloid complex (BLC) and hippocampal cornu ammonis areas 1 and 2 correlated with anxiety-like behavioral parameters. PV-positive neurons in the BLC of pSNL rats were predominantly changed in large-cell subtypes and were less activated. These findings indicate that anxiety-like behaviors emerge in the late phase of neuropathic pain and relate to PV-positive neurons in corticolimbic regions of pSNL rats.

Coupled versus decoupled visuomotor feedback: Differential frontoparietal activity during curved reach planning on simultaneous functional near-infrared spectroscopy and electroencephalography

INTRODUCTION

Interacting with the environment requires the planning and execution of reach-to-target movements along given reach trajectory paths. Human neural mechanisms for the motor planning of linear, or point-to-point, reaching movements are relatively well studied. However, the corresponding representations for curved and more complex reaching movements require further investigation. Additionally, the visual and proprioceptive feedback of hand positioning can be spatially and sequentially coupled in alignment (e.g., directly reaching for an object), termed coupled visuomotor feedback, or spatially decoupled (e.g., dragging the computer mouse forward to move the cursor upward), termed decoupled visuomotor feedback. During reach planning, visuomotor processing routes may differ across feedback types.

METHODS

We investigated the involvement of the frontoparietal regions, including the superior parietal lobule (SPL), dorsal premotor cortex (PMd), and dorsolateral prefrontal cortex (dlPFC), in curved reach planning under different feedback conditions. Participants engaged in two delayed-response reaching tasks with identical starting and target position sets but different reach trajectory paths (linear or curved) under two feedback conditions (coupled or decoupled). Neural responses in frontoparietal regions were analyzed using a combination of functional near-infrared spectroscopy and electroencephalography.

RESULTS

The results revealed that, regarding the cue period, curved reach planning had a higher hemodynamic response in the left SPL and bilateral PMd and a smaller high-beta power in the left parietal regions than linear reach planning. Regarding the delay period, higher hemodynamic responses during curved reach planning were observed in the right dlPFC for decoupled feedback than those for coupled feedback.

CONCLUSION

These findings suggest the crucial involvement of both SPL and PMd activities in trajectory-path processing for curved reach planning. Moreover, the dlPFC may be especially involved in the planning of curved reaching movements under decoupled feedback conditions. Thus, this study provides insight into the neural mechanisms underlying reaching function via different feedback conditions.

Impact of Exercise and Detraining during Childhood on Brown Adipose Tissue Whitening in Obesity

This study aimed to investigate the influence of childhood exercise and detraining on brown adipose tissue (BAT) whitening in obesity. Four-week-old male Long-Evans Tokushima Otsuka (LETO) rats (n = 9) and Otsuka Long-Evans Tokushima Fatty (OLETF) rats (n = 24) were used as non-obese and obese animals, respectively. OLETF rats were divided into non-exercise sedentary (n = 9) and exercise groups. OLETF rats in the exercise group were further divided into subgroups according to the exercise period—exercise from 10- to 12-weeks-old (n = 6); and exercise from 4- to 6-weeks-old, and detraining from 6- to 12-weeks-old (n = 9). At 12-weeks-old, immediately after exercise period, BAT whitening in OLETF rats was inhibited by exercise despite the fact that hypertrophy was not caused in the plantaris muscle. However, the effectiveness was attenuated during the detraining period. Histological BAT whitening and downregulation of uncoupling protein-1 (UCP-1) were found in non-exercise sedentary OLETF rats at 12-weeks-old. The downregulation was not inhibited, even though exercise histologically inhibited BAT whitening in OLETF rats. Childhood exercise decreased BAT whitening in obesity. Detraining attenuated the inhibition of BAT whitening. These results suggest that regular exercise is needed to improve BAT whitening and downregulation of UCP-1 in obesity.

Medial prefrontal area reductions, altered expressions of cholecystokinin, parvalbumin, and activating transcription factor 4 in the corticolimbic system, and altered emotional behavior in a progressive rat model of type 2 diabetes

Metabolic disorders are associated with a higher risk of psychiatric disorders. We previously reported that 20-week-old Otsuka Long-Evans Tokushima fatty (OLETF) rats, a model of progressive type 2 diabetes, showed increased anxiety-like behavior and regional area reductions and increased cholecystokinin-positive neurons in the corticolimbic system. However, in which stages of diabetes these alterations in OLETF rats occur remains unclear. We aimed to investigate anxiety-like behavior and its possible mechanisms at different stages of type 2 diabetes in OLETF rats. Eight- and 30-week-old OLETF rats were used as diabetic animal models at the prediabetic and progressive stages of type 2 diabetes respectively, and age-matched Long-Evans Tokushima Otsuka rats served as non-diabetic controls. In the open-field test, OLETF rats showed less locomotion in the center zone and longer latency to leave the center zone at 8 and 30 weeks old, respectively. The areas of the medial prefrontal cortex were smaller in the OLETF rats, regardless of age. The densities of cholecystokinin-positive neurons in OLETF rats were higher in the lateral and basolateral amygdala only at 8 weeks old and in the anterior cingulate and infralimbic cortices and hippocampal cornu ammonis area 3 at both ages. The densities of parvalbumin-positive neurons of OLETF rats were lower in the cornu ammonis area 2 at 8 weeks old and in the prelimbic and infralimbic cortices at both ages. No apoptotic cell death was detected in OLETF rats, but the percentage of neurons co-expressing activating transcription factor 4 and cholecystokinin and parvalbumin was higher in OLETF rats at both ages in the anterior cingulate cortex and basolateral amygdala, respectively. These results suggest that altered emotional behavior and related neurological changes in the corticolimbic system are already present in the prediabetic stage of OLETF rats.

Hemodynamic response during hyperbaric treatment on skeletal muscle in a type 2 diabetes rat model

Mild hyperbaric treatment prevents type 2 diabetes progression due to increased oxygen concentration and blood flow in skeletal muscle. However, it remains unknown whether this treatment is effective during all stages of type 2 diabetes. This study aimed to investigate the influences of hyperbaric treatment at 1.3 atmospheres absolute (ATA) on hemodynamic response in various stages of type 2 diabetes. Otsuka Long-Evans Tokushima fatty (OLETF) and Long-Evans Tokushima Otsuka (LETO) rats were used as models of type 2 diabetes and healthy controls, respectively. Glucose levels were significantly higher in OLETF rats than in LETO rats at all ages. Glucose intolerance gradually increased with age in OLETF rats. Insulin levels in OLETF rats were significantly higher at 20-week-old, however, were significantly lower at 60-week-old than in LETO rats. Oxy-Hb, total Hb, and StO₂ in skeletal muscle were increased during hyperbaric treatment in both rats. The hemodynamic changes were significantly higher in OLETF rats than LETO rats, and those changes were also pronounced at 8-week-old compared with other age in OLETF rats. These results suggest that hyperbaric treatment at 1.3 ATA acts on pathophysiological factors and the efficacy could be found only in the early stage of type 2 diabetes.

Region-specific brain area reductions and increased cholecystokinin positive neurons in diabetic OLETF rats: implication for anxiety-like behavior

Metabolic disorders can induce psychiatric comorbidities. Both brain and neuronal composition imbalances reportedly induce an anxiety-like phenotype. We hypothesized that alterations of localized brain areas and cholecystokinin (CCK) and parvalbumin (PV) expression could induce anxiety-like behavior in type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats. Twenty-week-old OLETF and non-diabetic Long-Evans Tokushima Otsuka (LETO) rats were used. The areas of corticolimbic regions were smaller in OLETF rats. The densities of CCK positive neurons in the lateral and basolateral amygdala, hippocampal cornu ammonis area 2, and prelimbic cortex were higher in OLETF rats. The densities of PV positive neurons were comparable between OLETF and LETO rats. Locomotion in the center zone in the open field test was lower in OLETF rats. These results suggest that imbalances of specific brain region areas and neuronal compositions in emotion-related areas increase the prevalence of anxiety-like behaviors in OLETF rats.

Case of asteroid hyalosis that developed severely reduced vision after cataract surgery

BACKGROUND

To report our findings in a patient with asteroid hyalosis (AH) who had a severe reduction of his visual acuity following cataract surgery. The vision was improved by vitreous surgery.

CASE PRESENTATION

The patient was an 81-year-old man. Following cataract surgery on his left eye, his decimal best-corrected visual acuity (BCVA) was markedly reduced from 0.2 to 0.02. A large number of asteroid bodies (ABs) was observed to be concentrated on the posterior surface of the implanted intraocular lens. Ultrasound B-mode images showed turbidity of the vitreous that was denser in the anterior vitreous where the ABs were concentrated. During vitrectomy, the ABs were observed to be concentrated in the anterior vitreous cavity, and a complete posterior vitreous detachment (PVD) was present. After vitrectomy successfully removed the ABs, the visibility of the fundus improved and the BCVA recovered to 1.0.

CONCLUSION

We suggest that the visual impairment after the cataract surgery was due to the concentrated ABs in the anterior vitreous cavity. The clustering of the ABs in the anterior vitreous cavity was most likely caused by the PVD that developed during the cataract surgery.

A Case of Uveal Colobomas Showing Marked Left-Right Difference in Diabetic Retinopathy

Purpose

Congenital uveal colobomas, including inferior iris and choroidal colobomas, are associated with microcornea and microphthalmia and often show left-right differences (laterality). The purpose of this study was to report a case of choroidal coloboma associated with left-right differences in diabetic retinopathy (DR).

Case

This study reports a 59-year-old male with bilateral iris and choroidal colobomas. The colobomatous area in the patient's right eye extended to the macula, and his right eye had been amblyopic since birth. The colobomatous area in his left eye was less extensive and did not involve the macula. Examination of the patient's left eye revealed multiple hemorrhages and hard exudates in the macula due to DR, but examination of his right eye showed almost no changes in DR, thus revealing a marked left-right difference. Optical coherence tomography showed more extensive retinal thinning in the patient's right eye than in his left eye. Fluorescein fundus angiography revealed a retinal nonperfusion area only in the left eye, and panretinal photocoagulation was subsequently performed.

Conclusion

Our findings show that the reason for the left-right difference in DR was attributed to the more severe choroidal coloboma and retinal thinning in the patient's right eye compared to his left eye, thus reducing oxygen demand, as is also seen in eyes with severe myopia.

A Case of Coats' Disease with Spontaneous Retinal Reattachment after Total Detachment

Purpose

To report a case of Coats’ disease in which spontaneous reattachment occurred after total retinal detachment.

Patient and Methods

A young boy (patient age: 4 years and 11 months) presented with leukocoria in the left eye. Slit-lamp examination revealed total retinal detachment with abnormal retinal blood vessels and subretinal exudation just behind the lens. Computed tomography imaging showed no solid mass lesion in the intraocular space. Secondary total retinal detachment as a complication of Coats’ disease was diagnosed. No light perception was detected, so we determined that surgical treatment was not indicated.

Results

Four months after the initial diagnosis, the retina showed complete reattachment with a large amount of subretinal hard exudate. Visual acuity remained unchanged, with no light perception.

Conclusions

We speculate that the spontaneous retinal reattachment in the present case was caused by the decreased permeability of the abnormal retinal vessels and the good functional effect of the retinal pigment epithelium.

[Case of retinal ischemia and retinal arteritis secondary to intravitreal nuclear drop]

BACKGROUND

A rare case of retinal arteritis and retinal ischemia as an incomplete branch retinal artery occlusion is reported following dropped lens fragments into the vitreous body.

CASE

A 69 year-old-woman had a cataract OD with corrected visual acuity of 0.4. When she underwent phacoemulsification on March 11, the posterior capsule was damaged and nucleus fragments dropped into a vitreous body. A few days later, the vitreous opacity increased. The corrected visual acuity OD dropped to 0.06 due to anterior chamber inflammation and the intraocular pressure increased to 26 mmHg. During a pars plana vitrectomy on May 7, some retinal whitening were observed and incomplete branch retinal artery occlusion was confirmed by fluorescence fundus angiography. The corrected visual acuity finally improved to 0.3, but the right visual field defect remained.

CONCLUSION

Incomplete branch retinal artery occlusion caused by phacoanaphylactic endophthalmitis secondary to lens fragments in the vitreous cavity seems to be a rare condition related to retinal whitening. The timing of pars plana vitrectomy should be considered before retinal arterial sheathing or retinal whitening can be noted.

The mode of transverse spread of contraction initiated by local activation in single crayfish muscle fibers

Isolated single crayfish muscle fibers were locally activated by applying negative current pulses to a pipette whose tip was in contact with the fiber surface. The contraction initiated by a moderate depolarization spread inwards in a graded manner according to the magnitude and duration of depolarization. Increase of the depolarized area increased the distance of the inward spread for a given amount of depolarization. If a large area of the surface membrane was depolarized with a large pipette for a sufficiently long time, the contraction spread not only inwards, but further transversely passing through the center of the fiber. Successive brief depolarizations given at an appropriate interval could produce contraction more effectively for a given amount of total current than did a prolonged depolarization. On the other hand, the contraction initiated by a strong negative current was observed to spread around the whole perimeter but not through the center of the fiber. Each type of local contraction always spread along the striation pattern and not longitudinally. Possible mechanisms of these responses are discussed in connection with the transverse tubular system of the muscle fibers.

Hyperpolarization and lysophosphatidylcholine induce inward currents and ethidium fluorescence in rabbit ventricular myocytes

Strong electric pulses produce reversible or irreversible membrane breakdown (electroporation). We analysed the permeation properties of minute pores caused by hyperpolarization or lysophosphatidylcholine (LPC) by comparing the amount of charge carried by irregular inward currents (I(hi)) with changes in ethidium bromide (EB) fluorescence in isolated rabbit ventricular myocytes. Forty-second negative pulses from a holding potential of -20 mV induced I(hi) whose conductance increased with hyperpolarization; the mean conductance (G(hi)) was 63.6 +/- 9.9 pS pF(-1) (mean +/- S.E.M., n = 9) at -160 mV. EB fluorescence increased during voltage pulses in parallel with the time integral of I(hi) (Q(hi)), with the magnitude of the increases in nuclear EB fluorescence being 5.3 times greater than in the cytoplasm at -160 mV. Similar hyperpolarization-induced parallel increases in I(hi) and EB fluorescence were also obtained in Na(+)-free, N-methyl-D-glucamine (NMDG) solution. LPC (10 microM) induced large (101.2 +/- 21.2 pS pF(-1), n = 16), rapid (rise times, 1-10 ms) I(hi) with slow relaxation rates at -80 mV that reflected increases in G(hi) to 94.3 +/- 24.8 pS pF(-1) (n = 8) at 6 min. Plots of EB fluorescence vs. Q(hi) were well fitted by a common Hill's equation with a Hill coefficient of 0.97. Taken together, our findings indicate that hyperpolarization and LPC produced pores having the same filter properties for the permeation of small ions, including ethidium(+), and that I(hi) (carried in part by Ca(2+)) generated by membrane breakdown are capable of supplying sufficient ions to evoke abnormal excitation and contraction in cardiac myocytes.

Independent modulation of L-type Ca2+ channel in guinea pig ventricular cells by nitrendipine and isoproterenol

Dihydropyridine (DHP) Ca2+ channel blockers decrease L-type Ca2+ channel current (I(CaL)) by enhancing steady-state inactivation, whereas beta-adrenergic stimulation increases I(CaL) with small changes in the kinetics. We studied the effects of DHP Ca2+ channel blockers on cardiac I(CaL) augmented by beta-adrenergic stimulation. We recorded I(CaL) as Ba2+ currents (I(Ba)) from guinea pig ventricular myocytes using the whole-cell patch clamp technique. and compared the effects of nitrendipine (NIT) in the absence and presence of isoproterenol (1 microM, ISO) or forskolin (10 microM, FSK). Maximal I(Ba) elicited from a holding potential of -80 mV were diminished to 69.4+/-13.5% (mean and SE, n=5) of control by NIT (100 nM) and the diminished I(Ba) were increased to 180.3+/-23.2% of control by ISO in the presence of NIT, which was similar to the enhancement seen in the absence of NIT. NIT shifted the V(1/2) of the I(Ba) inactivation curve from -34.6+/-1.9 mV (n=5) to -48.7+/-1.2 mV, enhancing I(Ba) decay with shortening T(1/2) at -10 mV from 164.6+/-24.2 ms (n=7) to 105.4+/-15.2 ms. ISO elicited a small additional shift in the V(1/2) of I(Ba) inactivation in the same direction. ISO and FSK each slowed I(Ba) decay in the absence of NIT, but not in its presence. Thus, beta-adrenergic agonists increase and DHP Ca2+ channel blockers decrease the amplitude of cardiac I(CaL) independently and the kinetics of I(CaL) is determined mainly by the latter when these drugs coexist.

Properties of voltage-gated Ca(2+) channels in rabbit ventricular myocytes expressing Ca(2+) channel alpha(1E) cDNA

Using the whole-cell patch-clamp technique, we have studied the properties of alpha(1E) Ca(2+) channel transfected in cardiac myocytes. We have also investigated the effect of foreign gene expression on the intrinsic L-type current (I(Ca,L)). Expression of green fluorescent protein significantly decreased the I(Ca,L). By contrast, expression of alpha(1E) with beta(2b) and alpha(2)/delta significantly increased the total Ca(2+) current, and in these cells a Ca(2+) antagonist, PN-200-110 (PN), only partially blocked the current. The remaining PN-resistant current was abolished by the application of a low concentration of Ni(2+) and was little affected by changing the charge carrier from Ca(2+) to Ba(2+) or by beta-adrenergic stimulation. On the basis of its voltage range for activation, this channel was classified as a high-voltage activated channel. Thus the expression of alpha(1E) did not generate T-like current in cardiac myocytes. On the other hand, expression of alpha(1E) decreased I(Ca,L) and slowed the I(Ca,L) inactivation. This inactivation slowing was attenuated by the beta(2b) coexpression, suggesting that the alpha(1E) may slow the inactivation of I(Ca,L) by scrambling with alpha(1C) for intrinsic auxiliary beta.

Activation of TxA2/PGH2 receptors and protein kinase C contribute to coronary dysfunction in superoxide treated rat hearts

We have previously shown that superoxide anion (O2-) stimulates the release of vasoconstrictor prostanoids and induces a prolonged rise in coronary perfusion pressure (CPP) that persists even after removal of O2-. In this study, we tested the hypothesis that the increased CPP is mediated by activation of TxA2/ PGH2 (TP) receptors and protein kinase C (PKC)-dependent mechanisms. In Langendorff perfused rat hearts, O2- was applied for 15 min and then washed out over a period of 20 min. Application of O2- increased the release of vasoconstrictive (TxA2 and PGF2alpha) and decreased vasodilating (PGI2 and PGE2) prostanoids. Although indomethacin (10 microM), a cyclooxygenase inhibitor, attenuated the rise in CPP during O2- perfusion, the increase was not completely blocked. OKY 046Na (10 microM), a thromboxane synthase inhibitor, had no effect on O2--induced increases in CPP, whereas ONO 3708 (10 microM), a TP receptor antagonist, suppressed this effect. PKC activity was also elevated by more than 50% by O2- perfusion. CPP typically increased throughout the O2- wash-out. This post-O2- vasoconstriction was not inhibited by indomethacin, nitroglycerin or nitrendipine. In contrast, ONO 3708 (10 microM) and two PKC inhibitors, staurosporine (10 nM) and calphostin C (100 nM), completely blocked the rise in CPP, and even elicited vasodilation. PDBu enhanced the post-O2- vasoconstriction. We conclude that O2--induced coronary vasoconstriction is initially mediated by TP receptors, but activation of PKC sustains the response.

Involvement of K(+) channels in the relaxant effects of YC-1 in vascular smooth muscle

This study addresses the question whether K(+) channels are involved in the vasorelaxant effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl-indazole (YC-1 ). In rat aorta, guinea pig aorta, and guinea pig a. carotis, YC-1 inhibited contractions induced by phenylephrine (3 microM) more potently than those induced by K(+)(48 mM). In rat aorta, tetraethylammonium (10 mM), charybdotoxin (0.2 microM), and iberiotoxin (0.1 microM), but not glibenclamide (10 microM), attenuated the relaxant effects of YC-1. In guinea pig a. carotis, YC-1 (30 microM) induced a hyperpolarisation which was antagonised by 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ; 50 microM). In rat aorta, YC-1 (30 microM) increased the rate constant of 86Rb-efflux. The effect of YC-1 was potentiated by zaprinast (10 microM), but inhibited by ODQ (50 microM) or charybdotoxin (0.2 microM). In smooth muscle cells from rat aorta, YC-1 (10 microM) increased BK(Ca) channel activity. It is suggested that YC-1-induced vasorelaxation is partially mediated by the activation of K(+) channels.

Properties and expression of Ca2+-activated K+ channels in H9c2 cells derived from rat ventricle

H9c2 is a clonal myogenic cell line derived from embryonic rat ventricle that can serve as a surrogate for cardiac or skeletal muscle in vitro. Using whole cell clamp with H9c2 myotubes, we observed that depolarizing pulses activated slow outward K+ currents and then slow tail currents. The K+ currents were abolished in a Ca2+-free external solution, indicating that they were Ca2+-activated K+ currents. They were blocked by apamin, a small-conductance Ca2+-activated K+ (SK) channel antagonist (IC50 = 6.2 nM), and by d-tubocurarine (IC50 = 49.4 microM). Activation of SK channels exhibited a bell-shaped voltage dependence that paralleled the current-voltage relation for L-type Ca2+ currents (ICa,L). ICa,L exhibited a slow time course similar to skeletal ICa, L, were unaffected by apamin, and were only slightly depressed by d-tubocurarine. RT-PCR analysis of the mRNAs revealed that rSK3, but not rSK1 or rSK2, was expressed in H9c2 myotubes but not in myoblasts. These results suggest that rSK3 channels are expressed in H9c2 myotubes and are primarily activated by ICa,L directly or indirectly via Ca2+-induced Ca2+ release from sarcoplasmic reticulum.

Activated stellate (Ito) cells possess voltage-activated calcium current

We previously reported stellate (Ito) cells possess voltage-activated Ca2+ current. The activation of stellate cells has been indicated to contribute to liver fibrosis and the regulation of hepatic hemodynamics. The aim of this study was to investigate the relationship between voltage-activated Ca2+ current and activation of stellate cells. Voltage-activated Ca2+ current in stellate cells isolated from rats were studied using whole-cell patch clamp technique. L-type voltage-activated Ca2+ current was hardly detected in stellate cells cultured for less than 9 days. Ca2+ current was detected 12.5 and 69% of cells at the 10th and 14th day of culture, respectively. BrdU incorporation indicated cell proliferation was recognized over 50% of cells at the 3rd and 5th day of culture, respectively, then decreased significantly in a time-dependent manner. On the other hand, the expression of alpha-smooth muscle actin indicated cell activation increased from 7th day of culture and collagen type I mRNA appeared remarkably in cells cultured for more than 10 days. In this study, we concluded L-type voltage-activated Ca2+ current was recognized in activated stellate (myofibroblast-like) cells.

Low K+-induced hyperpolarizations trigger transient depolarizations and action potentials in rabbit ventricular myocytes

1. The effects of large reductions of [K+]o on membrane potential were studied in isolated rabbit ventricular myocytes using the whole-cell patch clamp technique. 2. Decreasing [K+]o from the normal level of 5.4 mM to 0.1 mM increased resting membrane potential (Vrest) from -75.6 +/- 0.3 to -140.3 +/- 1.9 mV (means +/- s.e.m; n = 127), induced irregular, transient depolarizations with mean maximal amplitudes of 19.5 +/- 1.5 mV and elicited action potentials in 56.7 % of trials. The action potentials exhibited overshoots of 37.9 +/- 1.5 mV (n = 72) and sustained plateaux. 3. Addition of 0.1 mM La3+ in the presence of 0.1 mM [K+]o significantly increased Vrest but decreased the amplitude of transient depolarizations and suppressed the firing of action potentials. 4. Replacement of external Na+ or Cl- with N-methyl-D-glucamine or aspartate, respectively, or internal dialysis with 10 mM EGTA or BAPTA had little effect on low [K+]o-induced membrane potential changes. 5. Hyperpolarizing voltage clamp pulses to potentials between -110 and -200 mV activated irregular inward currents that increased in amplitude and frequency with increasing hyperpolarization and were depressed by 0.1 mM La3+. 6. The generation of transient depolarizations by low [K+]o can be explained as being a consequence of decreasing the inward rectifier K+ current (IK1) and the appearance of inward currents reflecting electroporation resulting from strong electric fields across the membrane.

Alcohol stimulates the expression of L-type voltage-operated Ca2+ channels in hepatic stellate cells

Hepatic stellate cells (HSCs) have L-type voltage-operated Ca2+ channels (VOCC). However, the effect of ethanol on VOCC is unknown. To investigate the mechanism of ethanol-induced liver injury, the effect of ethanol on VOCC in HSCs was studied. In control cells, VOCC revealed by patch clamp techniques were not detected in cells cultured for less than 7 days; however, a faint VOCC mRNA by reverse-transcription polymerase chain reaction was recognized at the 5(th) day of culture. Detection of VOCC increased from 8% on day 7 to over 50% on day 14 in controls. With ethanol (100mM), it increased from 12% on day 5 to 100 % on day 14. Furthermore, expression of alpha-smooth muscle actin, shown as transformation to a myofibroblast, was recognized in ethanol-treated cells earlier and stronger than that in controls. VOCC were up-regulated by the treatment with ethanol associated with the induction of transformation to myofibroblasts.

Superoxide and nitroglycerin stimulate release of PGF2 alpha and TxA2 in isolated rat heart

The aim of this study was to investigate the effects of nitroglycerin (NTG), a nitric oxide (NO) donor used as a vasodilating agent, on prostanoid [e.g., prostaglandin (PG)] release in the O2(-)-pretreated rat heart. Perfusion of O2-, generated by a xanthine oxidase-purine coupling, caused elevation (P < 0.05) of the coronary perfusion pressure (CPP) after 20 min (from 57.1 +/- 3.9 during the control period to 72.2 +/- 3.9 mmHg, P < 0.05). O2- caused increased release of PGF2 alpha from 3.6 +/- 0.7 to 20.6 +/- 4.4 pmol.min-1.g-1 and of thromboxane A2 (TxA2) from 2.4 +/- 0.4 to 9.6 +/- 1.6 pmol.min-1.g-1 (P < 0.001) with no significant changes in PGE2 and PGI2 release. During the 20-min washout of O2- from the heart with normal Krebs solution, release of PGF2 alpha and TxA2 decreased to 8.7 +/- 1.4 and 6.3 +/- 1.7 pmol.min-1.g-1, respectively, and the release of PGE2 and PGI2 markedly increased from 11.1 +/- 2.9 to 25.4 +/- 3.6 and 157.2 +/- 16.4 to 413.2 +/- 41.4 pmol.min-1.g-1, respectively (P < 0.05), without lowering the elevated CPP. Administration of 4 microM NTG during the washout period paradoxically augmented the elevated CPP to 133.3 +/- 0.6% and was associated with a doubling (P < 0.05) of PGF2 alpha and TxA2 release with no significant changes in PGE2 and PGI2 release. The NTG-induced CPP elevation was inhibited (P < 0.05) by indomethacin, a cyclooxygenase inhibitor, or ONO-3708, a TxA2 receptor blocker, whereas arachidonic acid, a substrate for PG synthesis, augmented the CPP elevation. These results indicate that NTG stimulates the synthesis of vasoconstrictive PG in the O2(-)-pretreated rat heart, inducing a paradoxical elevation in CPP.

Decrease in Ca2+ sensitivity as a mechanism of hydrogen peroxide-induced relaxation of rabbit aorta

OBJECTIVE

In vascular strips, hydrogen peroxide (H2O2) relaxes alpha 1-adrenergic agonist-induced but not high-K(+)-induced contractions. The aim of this study was to explore H2O2-induced changes in [Ca2+]i of vascular smooth muscle and to elucidate the mechanisms of action of H2O2.

METHODS

Isolated rabbit aortic strips were isometrically contracted with high-K+ (64.7 mM) or phenylephrine (PE, 0.3 microM). The effects of 300 microM H2O2 on [Ca2+]i of endothelium-denuded vascular smooth muscle and tension were determined simultaneously by the fura-2 method. Changes in [Ca2+]i were expressed as percentages of high-K(+)-induced values measured at the beginning of the experiments. In another series of experiments, the relaxant effect of 300 microM H2O2 was examined in high-K+ (20 mM)-induced contraction in the presence of the protein kinase C activator, phorbol 12,13-dibutyrate (PDBu).

RESULTS

Hydrogen peroxide caused a reversible rise in [Ca2+]i of vascular smooth muscle under both resting conditions and in the precontracted state. During high-K(+)-induced contraction, H2O2 further increased [Ca2+]i by 26.6(s.e.m. 1.7)% accompanied by a small increase in tension of 6.5(1.9)% of high-K(+)-induced tension. By contrast, during PE-induced contraction, although H2O2 caused a comparable additional increase in [Ca2+]i (26.4(4.7)%), muscle tension fell by 28.9(2.2)% of the steady-state PE-induced tension. Hydrogen peroxide had a relaxant effect on augmented high-K(+)-induced contraction in which Ca2+ sensitivity of the contractile apparatus was elevated by PDBu.

CONCLUSIONS

In spite of its effect of increasing [Ca2+]i of vascular smooth muscle, hydrogen peroxide causes relaxation of endothelium-denuded, PE-precontracted rabbit aorta. The mechanism is probably through suppression of agonist-induced augmentation of Ca2+ sensitivity of the contractile apparatus.

The tetravalent organic cation spermine causes the gating of the IRK1 channel expressed in murine fibroblast cells

1. The activation kinetics of the IRK1 channel stably expressed in L cells (a murine fibroblast cell line) were studied under the whole-cell voltage clamp. Without polyamines or Mg2+ in the pipettes, inward currents showed an exponential activation on hyperpolarization. The steep inward rectification of the currents around the reversal potential (Erev) could be described by the open-close transition of the channel with first-order kinetics. 2. When the tetravalent organic cation spermine (Spm) was added in the pipettes, the activation kinetics changed; this was explicable by the increase in the closing rate constant. The activation of the currents observed without Spm or Mg2+ in the pipettes was ascribed to the unblocking of the 'endogenous-Spm block'. 3. In the presence of the divalent cation putrescine (Put) or of Mg2+ in the pipettes, a different non-conductive state suppressed the outward currents on depolarization; the channels instantaneously changed to the open state on repolarization. As the depolarization was prolonged, this non-conductive state was replaced by the non-conductive state that shows an exponential activation on repolarization. This phenomenon was attributed to the redistribution of the channels from the Put- or Mg(2+)-blocked state to the 'endogenous Spm-blocked state' during depolarization. 4. In the presence of the trivalent cation spermidine (Spd) in the pipettes, two different non-conductive states occurred, showing a faster and a slower activation on repolarization. The rectification around Erev was mainly due to the non-conductive state showing a faster activation, which appeared to be the Spd-blocked state. During depolarization, redistribution of the channels to the 'endogenous Spm-blocked state' also occurred. 5. In the presence of Spd, Put or Mg2+ in the pipettes, the voltage dependence of the activation time constant reflecting the unblocking of the 'endogenous Spm' was shifted in the hyperpolarizing direction. 6. Our results suggest that the 'intrinsic gating' that shows the time-dependent activation on repolarization, and that is responsible for the inward rectification around Erev, reflects the blocking kinetics of the tetravalent Spm.

Depression of ATP-induced Ca2+ signalling by high K+ and low Cl- media in human aortic endothelial cells

We studied the contribution of the Cl- channel as well as K+ channel in the regulation of Ca2+ signalling in fura-2-loaded cultured human aortic endothelial cells. Low Cl- (20 mM) superfusion did not affect the ATP (10 microM)-induced [Ca2+]i increase at the initial peak (control 309 +/- 30 nM (mean +/- SD, n = 17) versus 20 mM [Cl-]o 308 +/- 40 nM (n = 8)) but depressed it at the sustained phase (at 5 min, 170 +/- 29 nM versus 85 +/- 10 nM). Similar selective depression of the sustained phase occurred also in Ca(2+)-free and 140 mM K+ solutions and in the presence of niflumic acid (300 microM), a blocker of the Cl- channel and Ca2+ permeable cation channel. After application of ATP, the increase of [Cl-]o from 20 to 146 mM resulted in a Ca2+ overshoot. Both Cl- and K+ channels play an important role in the regulation of Ca2+ influx presumably by controlling the membrane potential in vascular endothelial cells.

Inhibition of vasoactive amine induced contractions of vascular smooth muscle by hydrogen peroxide in rabbit aorta

OBJECTIVE

The aims were to investigate the effects of H2O2 on arterial contractions induced by vasoactive amine agonists and a high concentration of potassium ions (high K+) in vitro and to explore the possible underlying mechanism(s) involved.

METHODS

Isometric tension of rabbit isolated aortic strips was measured and the effects of pretreatment with H2O2 on contractions induced by phenylephrine and high K+ were compared. The effects of H2O2 on precontracted strips were determined in the presence and absence of the aortic endothelium and compared with those of acetylcholine.

RESULTS

The tension developed in response to an agonist was expressed as a percentage of the contraction induced by high K+ (64.7 mM) superfusion. Pretreatment with 300 microM H2O2 reduced the mean phenylephrine (0.3 microM) induced contraction from 96.2(SEM 1.4) to 61.8(2.8)%; the effect was stable and reversed by washing out the H2O2. Hydrogen peroxide relaxed phenylphrine precontracted strips with and without endothelium but it showed no relaxant effect when the strips were precontracted by high K+, whereas acetylcholine (1 microM) induced transient relaxation of high K+ precontracted strips by 27.8(2.9)%. The relaxant effect of H2O2 was not affected by pretreatment with indomethacin (a cyclo-oxygenase inhibitor), desferrioxamine (a hydroxyl radical scavenger), or diphenylphenylenediamine (a lipophilic antioxidant).

CONCLUSIONS

H2O2 inhibits vasoactive amine induced contractions of the vascular smooth muscle of rabbit aorta in vitro without affecting voltage dependent Ca2+ influx or contractile machinery. The mechanism responsible for its inhibitory effects may be related to impairments of the cellular signalling reactions initiated by the agonists.

L-type calcium channel activity in human atrial myocytes as influenced by 5-HT

5-Hydroxytryptamine (10 mumol/l; 5-HT) exerted a positive inotropic effect associated with an increase in the Ca2+ current (ICa) in the human right atrium. For detailed analysis, L-type Ca2+ channel currents were recorded from cell-attached patches using 100 mmol/l Ba2+ as charge carrier. Ca2+ channel activity was identified, first, by burst-like inwardly directed currents and, second, by the appearance of long channel openings promoted by Bay K 8644 (1 mumol/l) upon repetitive depolarizations from -80 to 0 mV. The unitary conductance of the Ca2+ channel amounted to 25.8 pS. During superfusion with 5-HT, ensemble averaged (mean) current was enhanced by about 60%. The increase in mean current was brought about by an increase in the channel availability, defined as the ratio of sweeps containing Ca2+ channel activity to the total number of depolarizations. The open probability of a single Ca2+ channel within a sweep with channel activity, unitary conductance, mean open and mean shut times of the channel, however, remained unaffected during superfusion with 5-HT (n = 10). The 5-HT-induced increase in macroscopic ICa in the human atrium can therefore be explained by an enhanced availability of Ca2+ channels to open upon depolarization. The observed changes in gating properties of the human Ca2+ channel by 5-HT are very similar to those which are known from isoprenaline-induced cAMP-dependent phosphorylation of the Ca2+ channel protein in other tissues.

[Recent progress of research on cardiac ion channels]

The paper summarizes the recent progress of research on the structure, function and regulation of cardiac ion channels. The primary structures of voltage-gated Na and Ca channels are homologous, with identical voltage sensors and homologous pore structure. The voltage-gated channels are modulated by sympathetic and vagal transmitters. beta-Stimulants phosphorylate various channels by activating cyclic AMP-dependent kinase, while acetylcholine antagonizes this phosphorylation. The phosphorylation inhibits the Na current by promoting inactivation, increases the L-type Ca current by increasing the channel availability, increases the delayed rectifying K current and induces Cl current. Acetylcholine induces a K current in nodal and atrial cells via a direct binding of beta gamma subunit of GTP-binding protein (GK) to the K channel.

Single-channel mechanism of beta-adrenergic enhancement of cardiac L-type calcium current

The cardiac L-type Ca2+ channel current is enhanced by beta-adrenergic stimulants by phosphorylation mediated by an increase in cyclic AMP. Single-channel studies have revealed that the Ca2+ channels are not always allowed to open at test steps from large negative holding potentials and beta-agonists increase the ratio of current-containing sweeps (availability, Ps). The duration of available (Ts) and unavailable states (TF) are measurable by applying a large number of test pulses. beta-Agonists shorten TF and prolong TS, possibly by enhancing channel phosphorylation by activating cyclic AMP-dependent protein kinase and by inhibiting channel dephosphorylation by phosphorylating phosphatase inhibitor 1, respectively, if the available state reflects the phosphorylated state of the channel. The modulation of the slow gating process, the increase in PS, plays a primary role in increasing the L-type Ca2+ current at moderate increase in sympathetic activity. When a larger increase in cyclic AMP is resulted, moduration of burst-kinetics including mode 2 openings also produced by phosphorylation enhances further the Ca2+ current.

[Acid-base balance and contraction of the cardiac muscle]

In cardiac muscle, intracelular pH (pHi) is regulated to close to 7.1, both by membrane transport systems (Na-H and Cl-HCO3 exchange) and intracellular H+ buffers. Internal acidosis depresses the contraction, while alkalosis increases it. Internal proton depresses the contraction even without altering the internal concentration of Ca (Cai). The proton blocks the Ca channels. However, as it releases membrane-bound Ca and the influx of Na via Na-H exchange increases Ca influx through Na-Ca exchange, pHi decrease is often accompanied by the Cai increases. The internal proton also affects the uptake and release of sarcoplasmic reticulum, Ca binding to troponin, actomyosin dynamics and variable catalytic processes.

Adrenoceptor-mediated effects on calcium channel currents are antagonized by 5'-(N-ethyl)-carboxamido-adenosine in guinea-pig atrial cells

In guinea-pig atrial myocytes, the effects of the adenosine analogue 5'-(N-ethyl)-carboxamido-adenosine (NECA) in the presence of isoprenaline (ISO) on Ca2+ channel activity were analyzed. Single Ca2+ channel currents were recorded from cell-attached patches by application of several hundred 100 ms depolarizing steps. Under control conditions, burstlike activity of channel openings during some depolarizing steps were followed by variably long periods of quiescence (blank sweeps). During superfusion with ISO (100 nmol/l), ensemble-averaged (mean) current was increased by about 150%. The underlying mechanism was found to be a significant increase in the channel availability, defined as the ratio of current-containing sweeps to the total number of sweeps. In addition, the ISO-induced reduction of blank sweeps was combined with slightly but not significantly higher values of the open probability in the current-containing sweeps. Open time and shut time histograms could be fitted by single and double exponential curves, respectively, which remained rather unaffected in the presence of ISO; accordingly, mean open time and mean shut time of the channel were not significantly changed by ISO. After the addition of NECA (1 mumol/l) in the presence of ISO, the ISO-induced increase in mean current was abolished. This effect of NECA on mean current was due to a reduction of the channel availability and a slight decrease in the open probability. The purinoceptor blocking agent 8-phenyltheophylline (10 mumol/l) antagonized the inhibitory action of NECA on the ISO-induced increase in Ca2+ channel activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Whole-cell K+ currents in isolated rabbit corneal epithelial cells

Membrane currents were recorded from enzymatically isolated cells from basal layers of rabbit corneal epithelium by the whole-cell clamp technique. Pipettes contained 140.4 mM KCl and extracellular K+ concentration was varied. The membrane currents on step voltage changes were rectangular currents with some fluctuations. The fluctuations disappeared near the zero-current potential. The reversal potential in normal Tyrode's solution with 5.4 mM K+ was -57.8 +/- 6.2 mV (mean +/- S.D., n = 10). Increasing [K+]o from 5.4 to 140.4 mM shifted the reversal potentials in the positive direction with a slope of 41.0 mV/decade. Concomitant depolarization of the resting potential was observed on increasing [K+]o. The whole-cell currents were blocked by Cs+ or Ba2+. These suggest that the major current component in the corneal epithelial cells in K+.

Mechanism of adenosine-induced inhibition of calcium current in guinea pig ventricular cells

The mechanism of adenosine-induced inhibition of Ca2+ currents was studied by recording single-channel Ca2+ currents from cell-attached patches on isolated guinea pig ventricular cells with pipettes containing 50 or 100 mM Ba2+. Numerous 100-msec depolarization steps were applied repetitively at 2 Hz from the resting potential of approximately -70 mV. The addition of 0.1 mM adenosine to the superfusate in the presence of 100 nM isoproterenol depressed the isoproterenol-induced increase in ensemble-averaged current: in peak amplitude, from 258 +/- 105% (mean +/- SD) (p less than 0.01) that of control in the presence of isoproterenol to 153 +/- 41% (n = 7) (p less than 0.05) by the addition of adenosine. In these patches, adenosine did not much affect the open probability in nonblank sweeps (control, 0.10 +/- 0.05; isoproterenol, 0.11 +/- 0.08; adenosine and isoproterenol, 0.08 +/- 0.05), but significantly decreased channel availability, defined as the rate of current-containing sweeps in total sweeps (control, 0.36 +/- 0.17; isoproterenol, 0.69 +/- 0.16 [p less than 0.01]; adenosine and isoproterenol, 0.45 +/- 0.20 [p less than 0.01]). The decrease of channel availability by adenosine was due to the shortening of the duration of the available state and the prolongation of that of the unavailable state. The depressive action of adenosine was suppressed by 0.1 mM theophylline. The single-channel conductance in the presence of 100 mM Ba2+ and Bay K 8644 was 26 pS and was not affected by isoproterenol or adenosine. We conclude that adenosine decreases Ca2+ current under beta-adrenergic stimulation mainly by reducing channel availability.

Modulation of slow gating process of calcium channels by isoprenaline in guinea-pig ventricular cells

1. The mechanism of enhancement of Ca2+ current by isoprenaline was studied by recording single-channel activity from cell-attached patches on isolated guinea-pig ventricular cells using patch pipettes containing 50 or 100 mM-Ba2+. 2. Isoprenaline (100 nM) increased the amplitude of ensemble average currents by increasing the rate of non-blank sweeps (availability). The current decay during 400 ms steps was significantly slowed by isoprenaline. However, the open probability for the non-blank sweeps elicited by 100 ms steps was only slightly increased by the application of isoprenaline. 3. The durations of the available state (TS) and the unavailable state (TF) were estimated by the number of non-blank and blank sweeps per run, respectively, applying repetitively 100 ms steps at 2 Hz. 4. At large negative holding potentials the distribution of TS was well fitted by an exponential curve, whose time constant was increased from 1.6 to 3.1 sweeps by 100 nM-isoprenaline, while TF distributed approximately single exponentially with a time constant of 2.0 sweeps in control and 1.3 sweeps in the presence of the drug. 5. At depolarized holding potentials a slow voltage-dependent component appeared in the histogram of TF and its time constant was markedly decreased by 100 nM-isoprenaline. 6. The availability-voltage relationship was simulated by the Boltzmann equation with a maximal value of 0.4 in the control. The maximal value was increased to 0.7 and the curve was shifted to a depolarizing direction by 7 mV by 100 nM-isoprenaline. 7. Isoprenaline increased the availability of cardiac Ca2+ channels by increasing the forward rate constant and decreasing the backward rate constant in both voltage-dependent and independent slow state transitions.

[Experimental study of periodontal tissue regeneration using biodegradable membranes]

This study was designed to investigate the effect on new attachment formation using a biodegradable membrane as a barrier to the regeneration of periodontal tissue. One-wall wide periodontal osseous defects with exposed root surfaces were prepared in three adult mongrel dogs. After surgical debridement of the periodontal defects, 3 types of biodegradable membranes, [Poly(L-lactic acid); (P-L-LA)] membrane, [Poly(lactic acid-co-glycolic acid); (PLGA)] (81: 19 mole%) membrane and PLGA (50: 50 mole%) membrane, were arranged to cover the denuded root surfaces. Specimen blocks were removed 8 weeks postoperatively for histological evaluation of their effect on the regeneration of periodontal tissue. The results were as follows: 1. Gingival regions containing P-L-LA or PLGA (81: 19 mole%) membranes showed delayed wound healing macroscopically. 2. Almost all P-L-LA membranes were present in the experimental sites failing to be resorbed during the 8-week experimental period. PLGA (81: 19 mole%) membranes were also present but showed with some degree of resorption and fragility, while PLGA (50: 50 mole%) membranes were completely resorbed. 3. This showed that the membranes used in this experiment are possible barriers to the generation of new attachment. It is important to make sure keeping the membrane. 4. There was no relationship between osteogenesis and cementogenesis. It seems that osteogenesis was depressed by membrane shrinkage and the gingival pressure which limited "the regenerative space of bone." 5. Moderate resorption was observed on the root surface, and new cementum was formed at the resorbed surface. 6. Ankylosis was observed between the new cementum and bone at the experimental sites. Newly formed cementum was seen on coronal sections of this area.

Voltage-dependent decrease in the availability of single calcium channels by nitrendipine in guinea-pig ventricular cells

1. The mechanism of Ca2+ channel block by nitrendipine was studied by recording single-channel activity from cell-attached patches on guinea-pig ventricular cells using patch pipettes containing 50 mM-Ba2+. Test depolarization pulses to around 10 mV with a duration of 100 ms were applied repetitively at 2 Hz. 2. The percentage of non-blank sweeps was maximal (about 40%) at a holding potential between -65 and -130 mV and decreased sigmoidally with its depolarization. Nitrendipine shifted the availability-voltage relationship in a hyperpolarizing direction. 3. From the number of consecutive non-blank sweeps and that of blank sweeps, the duration of the available state and that of the unavailable state were estimated. 4. The histogram of the duration of the available state showed a single-exponential distribution. Its mean duration was about 1.5 s and was shortened by nitrendipine. Correspondingly, the decay of the mean current during the depolarization step was accelerated by nitrendipine. 5. In the presence of 100 nM-nitrendipine the histogram of the duration of the unavailable state at large negative holding potentials was simulated as the sum of two exponential components, one with a time constant similar to that in the control and the other with a time constant of 6-7 s. 6. The histogram of the duration of the unavailable state at depolarized holding potentials was simulated by a double-exponential curve also in the control. The duration of the slow component was prolonged by nitrendipine. 7. The prolongation of the unavailable states initiated by drug binding during depolarization steps and maintained during depolarized holding potentials is the mechanism of the blockade. The rate constants of the state transitions between an available state and two unavailable states were estimated.

Maitotoxin-activated single calcium channels in guinea-pig cardiac cells

1. In order to clarify the mechanism of Ca-dependent excitatory action of maitotoxin (MTX), the most potent marine toxin known, patch-clamp techniques were used to analyse electrophysiological effects of MTX on guinea-pig isolated cardiac myocytes. 2. The whole-cell recordings showed that MTX (0.3 ng ml-1) produced a sustained inward current that was enhanced by adrenaline (2 microM) and abolished by Cd2+ (1 mM). 3. This current was predominantly carried by Ca2+ or Ba2+ and has an almost linear current-voltage relationship. 4. In cell-attached patches, MTX added to the pipette solution activated Ca channels with novel properties. The opening events of these channels occurred as long bursts, and the channel gating showed little voltage-dependence. 5. The unitary conductance was 12 pS in the presence of 50 mM Ba2+. Within a burst, the distribution of opening times was a single exponential with a mean open time of 10.4 ms. 6. The channel described here represents either a new class of voltage-independent Ca channel or an entirely modified form of voltage-gated Ca channel. This channel may account for the mechanism of enhanced Ca2+ influx through the cell membrane induced by MTX, and presumably regulates some ionic movements in myocardial cells.

Beta-adrenergic modulation of the slow gating process of cardiac calcium channels

Single Ca channel currents were recorded from isolated guinea pig ventricular myocytes in the presence of 50 mM Ba by the patch clamp technique under cell-attached configuration. When a constant short depolarizing pulse was applied repetitively, a single Ca channel opened in bursts during some depolarizing steps but completely failed to open in other steps. The opening probability of Ca channels in current-containing sweeps was little affected by adrenaline. There was a tendency for either failure, or success, in inducing a burst, to occur in clusters. The histogram of the number of successes between two failures showed a single exponential distribution with a time constant of 1-2 sec in controls and 2-4 sec in the presence of adrenaline (2 X 10(-6) M). The mean number of failures between two successes was diminished considerably by adrenaline. In ventricular myocytes adrenaline seems to increase the Ca current mainly by decreasing the rate of the Ca channel for the transition between one mode at which the channel is allowed to open on depolarization and other modes.

Elementary currents through Ca2+ channels in guinea pig myocytes

Elementary Ca2+ and Ba2+ currents were recorded from cell-attached membrane patches of ventricular myocytes from adult guinea pig hearts using the improved patch-clamp technique (Hamill et al. 1981). High concentrations of Ba2+ or Ca2+ (50 or 90 mM) were used in the pipettes to increase the signal-to-noise ratio. All data were derived from elementary current analyses in patches containing only one channel. 1) In response to voltage steps, channel openings occurred singly or in bursts of closely spaced unitary current pulses separated by wider shut intervals. During depolarizations of small amplitude from the resting potential, channel openings occurred almost randomly, whereas during larger depolarizations the events were grouped preferentially at the beginning. 2) Channel openings became more probable with increased depolarization; simultaneously, unitary current amplitudes declined in an ohmic manner. Elementary current amplitudes were slightly larger, when 50 mM Ba2+ replaced 50 mM Ca2+ in the pipettes (slope conductances 9 and 10 pS, respectively), but more than doubled, when Ba2+ was increased to 90 mM (slope conductance 18 pS). Clear outward currents through Ca2+ channels were not observed under these conditions. 3) Peak amplitudes of reconstructed mean currents doubled when 50 mM Ba2+ replaced 50 mM Ca2+ and were larger still when 90 mM Ba2+ was used in the pipettes. The current-voltage relations of the reconstructed mean currents showed a positive shift along the voltage axis as Ba2+ was increased or substituted equimolarly by Ca2+. correspondingly, the open state probability-voltage relations (activation curves) showed a parallel shift as Ba2+ was increased, which was less pronounced when Ba2+ was replaced equimolarly by Ca2+. 4) Determination of Ca2+ channel inactivation using 90 mM Ba2+ in the pipettes indicated an overlap with channel activation in a limited voltage range, resulting in a steady-state "window" current. Inactivation can occur without divalent cation influx. 5) Formation of an inside-out patch resulted in a fast rundown of elementary Ca2+ channel currents. 6) Channel openings were often grouped in bursts. The lifetimes of the open state, the bursts, and the closed states were estimated for Ba2+ and Ca2+ as permeating ions. At least two exponentials were needed to fit the histogram of the lifetimes of all closed states. The lifetimes of the individual openings and bursts were mono-exponentially distributed. The kinetics of the Ca+ channel depended on the voltage and the permeating ion. During +30 mV depolarizations, no significant effect on the permeating ion on channel gating could be detected.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical decoupling by Sr action potentials in guinea-pig papillary muscle

The membrane constants of guinea-pig papillary muscle have been derived by cable analysis, utilizing a single sucrose gap and micro-electrode recordings. In Na-free 20 mmol/l Sr Tyrode, the longitudinal resistance (ri) was increased by 210% from the control value after the passage of ten action potentials (APs) and by 457% after twenty APs but this increase in ri was reversibly abolished by perfusing with Na-containing solutions. ri was not affected by stimulation in Na-containing 20 mmol/l Sr Tyrode. Concomitant with the increase in ri, the conduction velocity of Sr APs was decreased from the control level of 8.6 to 3.1 cm/s after about twenty evoked Sr APs. The twitches elicited in the Na-free Sr Tyrode were large but the relaxation time was comparatively slow (20-30s), whereas those elicited in the Na-containing Sr Tyrode had a large amplitude and relaxation occurred within a few seconds. It is suggested that the increase in ri is due to junctional decoupling, produced either directly, by an intracellular accumulation of Sr2+, or indirectly by an increase in intracellular H+.

Inhibition of the slow inward current and the time-dependent outward current of mammalian ventricular muscle by gentamicin

The aminoglycoside antibiotic, gentamicin (GM), depressed the plateau phase and shortened the duration of the action potential in guinea pig papillary muscle. Its effect on the membrane currents was studied by a single sucrose gap voltage clamp method. The slow inward current (is) was remarkably diminished by GM with little change in its time course, in the voltage-dependency of the steady-state inactivation and activation or in its reversal potential. The maximal amplitude of is, obtained by subtracting the Co2+-resistant current, was reduced to 57% by 0.1 mmol/l GM and almost reduced to zero by 1 mmol/l GM. The efficacy of GM in inhibiting (is) was reduced by increasing the external Ca2+ concentration from 1.8 to 5.4 or 10.8 mmol/l, but not by the application of adrenaline. The time-dependent outward current (ik) was also decreased by GM but only at higher concentrations. It is proposed that the depressant action of GM on is was due to a blockade of slow channels, whereby GM may have dislocated Ca from the binding sites at slow channels on the external surface of the membrane.

The ionic mechanism of prolongation of action potential duration of cardiac ventricular muscle by anthopleurin-A and its relationship to the inotropic effect

Anthopleurin-A (AP-A) prolonged the duration of action potential and increased the developed tension of isolated guinea-pig and canine ventricular muscle. Voltage clamp experiments by using a single sucrose gap method were performed to investigate the ionic mechanism of the prolongation of the action potential in guinea-pig ventricular muscle. The prolongation of action potential by AP-A was accompanied by a decreased net outward current in a quasi-steady state. The slow inward current and the delayed potassium current were not changed by AP-A. The prolongation of action potential by AP-A was reversed by tetrodotoxin, thus it was concluded that AP-A induced tetrodotoxin-sensitive inward current which lasted long after the initial fast Na current. Modification of the AP-A-induced positive inotropic effect was also examined by using the canine blood-perfused ventricular muscle and was consistent with the above electrophysiological effects; tetrodotoxin, not nifedipine, suppressed percent changes produced by AP-A and also that by veratrine.