Effects of lemakalim and thalium on early afterdepolarization in mouse atrial fibers

The effects of lemakalim (BRL 38227) and thallium ion (Tl) on action potential (AP) and on early afterdepolarization (EAD) were studied in mouse atrial fibers. Under treatment with lemakalim (25 mcM) or Tl (0.2 mM), the AP was not significantly changed except for the reduction of duration of AP (APD). EAD induced by 3.0 mM K superfusion was abolished by 50 mcM lemakalim and only partially inhibited or was not effected under 25 mcM lemakalim. However, EAD was abolished completely and rapidly by Tl treatment. With addition of K concentration in superfusate to 5.0 mM the EAD could only be partially inhibited. By further increasing the K concentration to 7.0 mM the EAD could be completely abolished. It is suggested that the activator of outward current could inhibit EAD as well as the blockers of inward currents.

Effects and mechanism of low [K]o on the critical potential of effective refractory period in guinea pig ventricular muscle cells

1.5 mM KCl Tyrode's solution enabled the critical potential (-55-60 mV) of effective refractory period to shift in a positive direction in guinea pig ventricular muscle cells. In 1.5 mM KCl Tyrode's solution, the probability of testing AP's initial potential positive to -54 mV in the repolarizing phase was as high as 80% (n = 10), but the percentage in 4.5 mM [K]o group was only 11% (n = 35). The mean value of the positive shift was 30.2 +/- SD 17 mV. Testing APs had higher values of overshoots (mean = 23 +/- 13.8 mV); their mean Vmax was 98 V/s. Early after depolarization and positive inotropic effects appeared. 13.5 mM KCl, in contrast to 1.5 mM KCl, produced contrary effects. Phenomena indicated that early after depolarization in low [K]o was associated with the positive shift of critical potential of effective refractory period. Above-mentioned effects of 1.5 mM KCl could not be completely eliminated by verapamil, but could be abolished by an inactivation promoting agent of sodium channel, lidocaine 7.4 x 10(-5) M (n = 10). The results suggest that accelerating recovery time and shifting recovery potential in the positive direction of inactivated sodium channel might be the principal reasons for the effects of low [K]o. The role of the Na+ pump inhibitor, ouabain, was not similar to that of 1.5 mM KCl Tyrode's solution except for positive inotropic effect.

Role of afterhyperpolarization in termination of early afterdepolarization in mouse atrial fibers

Afterhyperpolarization (AHP) following triggered burst in early afterdepolarization (EAD) was investigated in mouse atrial fiber treated with aconitine or ryanodine. In both cases, a long second plateau (SP) with or without intermittent trains of bursts could be observed in certain conditions. Repolarization potentials were measured both in normal EAD (cycle lengths of 1-5 sec) and in EAD with a long SP. The values of repolarization potentials were almost constant, around -61 mV, in both situations. AHP could be recorded at the end of the intermittent bursts or after a burst elicited by an electrical stimulation on the long lasting SP. When the voltage of AHP attained the repolarization potential, rapid repolarization started instantly leading to complete repolarization of the EAD. It is suggested that AHP in EAD or following a burst elicited by stimulation enhances the termination of EAD.

[Effects of nicardipine on automaticity of sinoatrial node in rabbit heart]

The dual effects of nicardipine (Nic) on the automatic activity of sinoatrial (SA) node cell in rabbit heart had been observed using intracellular microelectrodes. Superfused with Nic 0.1, 0.5, 1.0, and 5.0 mumol.L-1 for 10 min, the spontaneous rate was decreased by 32%, 42%, 47%, and 69%, respectively. However, by superfusing with Nic 0.05 mumol.L-1, the spontaneous rate and the amplitude of action potentials were increased by 12% and 13% respectively. Nic 5.0 mumol.L-1 inhibited the positive chronotropic effects of isoproterenol and nicotine. The results suggest that Nic may block the calcium influx in SA node cells.

Recent developments in diagnosis and treatment of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is one of the major cancers that Chinese radiotherapists have to treat, because of its high incidence which shows a tendency to increase. Although results of radiotherapy in NPC have improved markedly during the last decade, treatment at an early stage of the disease is the most effective. It is therefore important to make the diagnosis early, and recently serological surveys by IgA/VCA show its efficacy in high risk populations. Histological diagnosis so far has not correlated to prognosis, and new histological classifications have been proposed by many authors. The importance of CT scans in diagnosis and treatment is stressed. Criteria for clinical staging of NPC will have to be reconsidered, especially the T staging, as 80% of cases formerly classified as T1 may already have paranasopharyngeal extension, as shown on CT scans. The technique of radiotherapy has not changed much essentially since the advent of telecobaltherapy. However, various institutions have their own special variations. The most striking advance is the use of high-dose rate afterloading brachytherapy as boost for residual disease or as main treatment for nasopharyngeal recurrences. Finally, the role of chemotherapy in the radiation treatment of NPC is discussed, and the paper concludes with some remarks on the future outlook in the diagnosis and treatment of NPC.

Role of take-off potential and second plateau response in generation of early afterdepolarization in arterial fibers of mouse heart

Take-off potentials (TOPs) of triggered bursts were studied on aconitine- 3.0 mM K+ and quinidine-induced early afterdepolarization (EADs) in mice atrial fibers. TOPs varied from -40 to -66 mV (-53.4 +/- 6.4 mV, n = 14) depending on the cycle length of stimulation. TOPs were cycle length-dependent and the relationship between TOP and cycle length was exponential. Before the generation of EAD, a second plateau appeared following the rapid repolarization phase of action potential (AP). In some preparations, EAD could not be induced, especially at a shorter cycle length, leaving a definite second plateau following the AP under treatment with effective agents. By application of a premature stimulation on the second plateau, only one burst could be observed. However, two or more bursts could be induced when a stimulation was applied on the rapid repolarization phase at -50 +/- 6 mV (n = 17) level. We defined this phenomenon as "second plateau response" which was studied in the present work under treatment with quinidine (4 cases), 3.0 mM K+ (4), ryanodine (6) and Bay K 8644 (3). The second plateau response was abolished by tetrodotoxin (1.0 microM), nifedipine (2.0 microM) or rapid driving. All of these were similar to the properties of the EAD. It is suggested that the second plateau response may be taken as an indicator of the capability of the EAD generation in myocardiac cells.

Early afterdepolarization induced by ryanodine in atrial fibers of mouse heart

The effects of ryanodine on the action potential and induction of early afterdepolarization (EAD) were studied in the atrial fibers of mouse heart. Under treatment with ryanodine, the duration of the action potential (ADP) was prolonged. The percentage of the prolongation of ADP25, APD50 and ADP100 were 83, 49 and 20%, respectively, at a cycle length of 1 sec driving stimulation. As the cycle length was prolonged (from 0.5-10 sec), EAD could be induced in 10 of 16 preparations showing exponential relationship with the cycle length. Tetrodotoxin, lidocaine and nifedipine inhibited the induction of EAD. In 6 preparations in which the EAD was not induced, more than one burst could respond to a single premature stimulation applied in the early phase of repolarization, which was defined as second plateau response. The mechanism of ryanodine-induced EAD has been investigated.

[Effects of nicotine on action potentials of guinea pig and rabbit papillary muscles]

The electrophysiological action of nicotine was studied by microelectrode technique on isolated guinea pig and rabbit papillary muscles. Nicotine had no significant effect on RP, APA and Vmax; but its biphasic effect on APD35, APD90 and ERP were observed in different concentrations, ie: high concentration (604 mumols/L) prolonged APD35, APD90 and ERP by 27.3, 26.0 and 26.1% respectively, whereas low concentration (0.6 mumol/L) shortened them by 49.6, 40.0 and 27.6%, respectively. It is suggested that high concentration of nicotine may enhance the calcium influx, but low concentration decrease it.

Early afterdepolarization in mouse atrial fibers induced by 3.0 mM K+ and the inhibitory effects of tetrodotoxin and nifedipine

Early afterdepolarization (EAD) was induced under superfusion of Tyrode solution (K+ = 3.0 mM) at a longer cycle length in mouse atrial fibers. The relationships between the duration and the number of triggered bursts and cycle length were exponential (n = 17). Thus, EAD possesses the property of cycle length dependence. Under a moderate concentration of TTX (4.0 microM) or nifedipine (5.0 microM) treatment, EAD was partially inhibited but maintained cycle length dependence. When a high concentration of the drugs (30 microM and 8.0 microM, respectively) was applied, EAD was abolished at all cycle lengths of driving stimulation. It is suggested that both inward currents (INa and ICa) are involved in the generation of EAD in mouse atrial fibers.

[Effects of sodium vanadate on action potentials of guinea pig papillary muscles]

Sodium vanadate (NaVO3, 800 mumol/L) diminished the plateau phase and the action potential duration of the action potentials in guinea pig ventricular fibers (VF). 200 mumol/L also reduced the maximal rate of depolarization of slow action potentials in the partial depolarized VF under high K superfusion and inhibited the delayed after depolarization induced by adrenalin. It is suggested that NaVO3 may inhibit the slow channel current and does not reduce the sodium pump activity in VF significantly when it was used extracellularly.

[Effects of nicotine on automaticity of sinoatrial node in rabbit heart]

The electro-physiological effects of nicotine on sinoatrial node cells in rabbit heart were studied using intracellular microelectrodes. When superfused with nicotine 604.0, 60.4, 6.0 or 0.6 mumol/L the spontaneous rate stopped or decreased for 20 s and then increased, eventually surpassing the control values 50 +/- 13, 45 +/- 12, 23 +/- 10 and 14 +/- 6%, respectively. The inhibitory phase was blocked by atropine and the excitatory phase was eliminated by tubocurarine chloride, hexamethonium bromide or pindolol. These results suggest that the effects observed may be related to cholinergic system and caused by nicotine induced catecholamine release.

10-year survival rate for patient with nasopharyngeal carcinoma after radiation therapy. Clinical analysis of 367 cases

Of 1,344 patients with nasopharyngeal carcinoma treated during 1961-1965 at the Shanghai Cancer Hospital, 367 who survived over 10 years after radiation therapy, were analysed. The results showed that the patients with stage I, II nasopharyngeal carcinoma and those with stage III, IV, the 10-year survival rates were 41.5% and 22.8% respectively, the overall 10-year survival rate being 27.3%. The 10-year survival rate was higher for female patients than for males, and was not related to the age of the patients and the pathological type of this carcinoma. The optimal tumor dosage was thought to be 60-70 Gy 350(95.4%) out of the 367 patients received radiotherapy only once. The rest received repeated irradiation for recurrence. For the reirradiated patients, the 10-year survival rate was 13.5%. Most recurrences occurred 5 years after radiotherapy (12/17), and only 5 within 3 years.

Radiation survival properties of cultured human gastric adenocarcinoma cells and the effect of AT-1727

Tumor cells (SGC-7901) obtained from a human gastric adenocarcinoma have been examined with regard to their intrinsic sensitivity to gamma-irradiation and as to how this intrinsic sensitivity might be altered by growth in a synthesized agent AT-1727 (N4-morpholino-methyl-3,5-dioxopiperazynyl-1,2 ethanl). Clonogenic survival was measured via colony formation assays and fitted to single-hit-multitarget formula. Exponentially growing cells exhibited the mean of survival parameters: D0 = 0.86 + 0.04 Gy; n = 7.03 + 2.3; Dq = 1.63 + 0.23 Gy and SF2 (surviving fraction of conventional daily clinical dose of 2 Gy) = 45-50%. Split-dose survival assays and delayed plating methods were used to exploit the capacity of sublethal damage repair of this cell line studied demonstrating the reappearance of initial shoulder on the survival curve and an increased survival. Alteration of radiosensitivity of SGC cells by AT-1727 was shown when cultures were incubated in a medium with the drug for a 6 hr interval between split dose irradiation, indicating the inhibition of sublethal damage repair. The radioresistance of hypoxic SGC cells was decreased when pre-treatment with AT-1727 was given 2 hr before irradiation, and the decrease of surviving fraction was drug-dose dependent. A maximum enhanced effect was obtained when 0.15 mM of AT-1727 was used, reaching an ER of 1.24. Inhibition of sublethal damage repair and action as a hypoxic radiosensitizer were considered to be two parts of the mechanism of AT-1727 in modification of radiation effects.

Intracavitary radiation treatment of nasopharyngeal carcinoma by the high dose rate afterloading technique

Sixty-four patients with nasopharyngeal carcinoma were treated by various combinations of external irradiation with intracavitary radiotherapy using the high dose rate afterloading technique. The afterloading intracavitary radiation (AIR) was given as a routine boost or for residual or recurrent disease. The external irradiation dose varied from 45 to 70 Gy, whereas the AIR dose ranged from 10-50 Gy, depending on the nature of the primary nasopharyngeal lesion. The results were quite encouraging, although the longest follow-up so far has only been just over 4 years. Of 13 such cases that received external radiotherapy plus AIR as primary treatment, 12 have survived. However, of the 9 cases who received AIR for local recurrence after external radiotherapy, only 5 survived. Of the total of 64 cases treated by AIR from June 1981 to May 1986, 54 are alive. No serious radiation sequelae have been observed. It can be concluded that AIR for nasopharyngeal carcinoma is indicated for boosting the dose to the nasopharyngeal cavity with appropriate reduction in external irradiation dose, and for residual or recurrent disease after primary external radiotherapy.

DNA flow cytometric analysis of human nasopharyngeal carcinoma in nude mice

The tissue from a patient with nasopharyngeal carcinoma has been transferred to nude mice (BALB/c), and has successfully been growing through twenty passages. The tumors in the nude mice and primary human tumor have been examined for the cellular DNA content by FCM and also conventional pathological examination, chromosome analysis, and EBV test. The tumor take rate varied markedly in different passages with a mean value of approximately 70%, and showing a tendency to increase. The tumor doubling time within 6-12 weeks after transplantation of six tumors in 18 and 20 passages were 14.8 and 9.3 days respectively. However, the tumor volume at 12 weeks varied significantly, ranging from 438 to 1998 mm3. By FCM, it has been found that the values of DNA index were about the same in both primary tumor and the tumors in nude mice. The distribution of various phase cells in cell cycle was also about the same in both. In conclusion, the application of FCM to examine the cellular DNA content of the tumor in nude mice is a rapid and sensitive method, useful in the investigation on the stability of biological characteristics of human NPC in nude mice and in further studies on the effects by various therapeutic methods.

K+-free induced early afterdepolarization in cardiac ventricular fibers of guinea pig after cold treatment

The genesis and elimination of early afterdepolarizations (EADs) have been investigated in guinea pig cardiac ventricular fibers after a short period of cooling (5 h, 2-4 degrees C). After rewarming them to 37 degrees C, EADs could be induced by K+-free superfusion at an appropriate driving stimulation (0.2 Hz) in all preparations. A high level plateau, which linearly increases its duration with time, appears ahead of EADs. The critical point of the plateau occurred steadily, at the level of -47 +/- 4 mV. Two types of triggered activity, all of which are the rhythmic activities in low level of membrane potential (-50 to -60 mV), appear on the plateau. There is no significant change after overdriving. Agonists of the Na-K pump (K+ and T1+) could stop the rhythmic activity immediately and turn the low level of membrane potential to high one. The results showed that high level plateau is the basis of genesis of EADs, and the activation of Na-K pump plays an important part in stopping triggered rhythms arising from EADs.

Fluorescence of hematoporphyrin in living cells and in solution

The fluorescence properties of hematoporphyrin (Hp) and its derivative (HpD) were investigated in leukemia cells and in normal lymphocytes under a microscope, and the results were compared with those in solution. The spectra and the time behaviour of Hp (or HpD) fluorescence in living cells were found to be almost the same as those in Hp solution of very high concentration. This implies that Hp is much more concentrated in the cells than in the medium. It was also found that irradiation with intense light easily gives rise to a photoproduct which gives an additional peak in the fluorescence spectrum. Possible methods to increase the sensitivity of cancer detection and localization are discussed.

Permeance of Novikoff hepatoma gap junctions: quantitative video analysis of dye transfer

Fluorescent dyes are commonly used to study permeable (gap) junctions, but only rarely have quantitative values for junctional dye permeability been determined. In the present study, junctional permeance (PA, i.e., the product of the junctional permeability coefficient, P, times the junctional area, A) to Lucifer Yellow CH (LY) has been obtained for pairs of Novikoff hepatoma cells. Dye was microinjected into one cell and the subsequent transfer monitored by a SIT camera and recorded on video tape. The intensities of fluorescence in the injected and "recipient" cell were measured using a Digisector (Microworks) digitizing board and an Apple II Plus computer to analyze the video records. These changes in intensity, along with an estimate of volume of the spherical cells, were used to calculate the junctional permeance (PA) of cell pairs according to Fick's diffusion equation. Junctional permeances show considerable variation ranging from 0.08 X 10(-11) to 27.0 X 10(-11) cm3/sec. Using the mean PA and a previous estimate of the mean number of junctional channels per interface in the Novikoff cultures, a value for diffusion coefficient of LY through gap junctions is calculated to be about 1.4 X 10(-6) cm2/sec. There is a general proportionality between mean PA and cell volume for hepatoma cell pairs of a certain size range. Such a relationship between cell volume and junctional capacity suggests one source of variation of PA. Other possible sources, e.g., related to position in the cell cycle, are discussed.

Junctions between lens cells in differentiating cultures: structure, formation, intercellular permeability, and junctional protein expression

We previously described cultures of chick embryo lens cells which displayed a marked degree of differentiation. In this report, the junctions found between the lens fiber-like cells in the differentiated "lentoids" are characterized in several ways. Thin-section methods with electron microscopy first demonstrated that numerous, large junctions between lentoid cells accompanied the other differentiated features of these cells. Freeze-fracture techniques, including quantitative analysis, then revealed that (a) junctional particles were loosely arranged as is typical of fiber cells, (b) the population of individual junctional areas in culture was indistinguishable from that found in 10- to 12-day chick embryo lenses, and (c) apparent junction formation occurred during the development of the lens cells, with lacy arrays of particles being associated with fiber-like junctions. In addition, gap junctions with hexagonally packed particles, typical of lens epithelial cells, largely disappeared during the course of differentiation. Injection of tracer dyes into lentoid cells resulted in rapid intercellular movement of dye, consistent with functional cell-to-cell channels connecting lentoid cells. During the development of the lens cells in culture, as junction formation occurred, an increase of approximately eight-fold in MP28 protein was observed within the cells. These combined results indicate that (a) extensive lens fiber junctions and functional cell-to-cell channels are found between differentiated lentoid lentoid cells in vitro, (b) lens fiber junctions appear to form during the course of lens cell differentiation in culture, (c) a significant increase occurs in the putative junctional protein before the cultures are highly developed, (d) the increased levels of MP28 and junction formation may be required for the full expression of the differentiated state in the lens fiber cell, and (e) this culture system should prove to be valuable for additional experiments on lens junctions and for other studies requiring the development of lens fiber cells in vitro.

[Flow cytometer (FCM) in biological characteristics of nasopharyngeal carcinoma xenografts in nude mice]

Tumor tissue from a patient with nasopharyngeal carcinoma was transplanted to nude mice (BALB/c) and had successfully been maintained through ten passages. The nude mice tumor and the primary human tumor were assayed by FCM for the DNA content in addition to conventional pathological examination, chromosome analysis and EBV assay. The tumor incidence in the different passages showed a marked change ranging from 25% to 81% with a mean value of 52% which tended to increase, however. The doubling time of six tumors in the ninth passage showed no great change 6-12 weeks after transplantation with a mean about 4.3 days. But at week 12, there was a significant difference between each tumor volume, ranging from 438 to 1,998 mm3. By FCM, it was found that the DNA index remained constant in both the primary and nude mice tumors. Among the nude mice tumors in different passages, the distribution of various phase cells in cell cycle was similar to that of the primary tumor. In conclusion, the use of FCM to assay the cellular DNA content in nude mice tumor is rapid and sensitive. It is helpful, for the nude mice tumor, in identifying stability of the biological characteristics and in studying of the mechanism of chemotherapy and radiotherapy in the future.

Preliminary report on AT1727 as a potential radiosensitizer

AT1727 is a derivative of ICRF 154. The purpose of this study was to evaluate its "radiosensitizer" properties. From October 1979 until the end of December 1980, 89 patients with radiation resistant cancers such as soft tissue sarcoma, squamous lung cancer (with large lesion, 6-8 cm diameter) and other cancers had been included in trial. Radiation therapy was carried out using CO60 or 8 Mev Linac. Fifty-five patients had a remarkable objective remission rate of 61.8% (55/89). Eighteen of 30 patients with soft tissue sarcomas obtained obvious remission (60%), and 26 of 38 patients with lung cancer had remission (68.4%). Patients with esophageal cancer (5/6) and nasopharyngeal cancer (5/5) also had good remission rates. The side-effects of this treatment were very mild: anorexia and vomiting were noted in 50% and no significant changes were noted in liver and kidney function tests and blood platelet count. Leucopenia was slight in all but one patient. No difference in the lung fibrosis rate was noted between the two randomized groups. From the results of this study we concluded that AT1727 had some effect as a "radiosensitizer" but much more work is needed to confirm this.