Na/Ca exchange and Na/K-ATPase function are equally concentrated in transverse tubules of rat ventricular myocytes

Formamide-induced detubulation of rat ventricular myocytes was used to investigate the functional distribution of the Na/Ca exchanger (NCX) and Na/K-ATPase between the t-tubules and external sarcolemma. Detubulation resulted in a 32% decrease in cell capacitance, whereas cell volume was unchanged. Thus, the surface-to-volume ratio was used to assess the success of detubulation. NCX current (I(NCX)) and Na/K pump current (I(pump)) were recorded using whole-cell patch clamp, as Cd-sensitive and K-activated currents, respectively. Both inward and outward I(NCX) density was significantly reduced by approximately 40% in detubulated cells. I(NCX) density at 0 mV decreased from 0.19 +/- 0.03 to 0.10 +/- 0.03 pA/pF upon detubulation. I(pump) density was also lower in detubulated myocytes over the range of voltages (-50 to +100 mV) and internal [Na] ([Na](i)) investigated (7-22 mM). At [Na](i) = 10 mM and -20 mV, I(pump) density was reduced by 39% in detubulated myocytes (0.28 +/- 0.02 vs. 0.17 +/- 0.03 pA/pF), but the apparent K(m) for [Na](i) was unchanged (16.9 +/- 0.4 vs. 17.0 +/- 0.3 mM). These results indicate that although thet-tubules represent only approximately 32% of the total sarcolemma, they contribute approximately 60% to the total I(NCX) and I(pump). Thus, the functional density of NCX and Na/K pump in the t-tubules is 3-3.5-fold higher than in the external sarcolemma.

High-dose chemotherapy in high-risk myelodysplastic syndrome: covariate-adjusted comparison of five regimens

BACKGROUND

Antileukemic chemotherapy has been used for two decades to treat high-risk myelodysplastic syndrome (refractory anemia with excess of blasts [RAEB] and RAEB in transformation into acute leukemia [RAEB-t]) patients. Because the results of standard regimens have been disappointing, high-dose chemotherapeutic regimens were investigated recently. In the absence of randomized trials, the relative merits of various treatment regimens are unknown.

METHODS

The authors analyzed the outcome for 394 newly diagnosed patients treated between 1991 and 1999 with five regimens consisting of intermediate- or high-dose cytosine arabinoside (A) in combination with idarubicin (I), and introduced cyclophosphamide (C) and the new agents fludarabine (F) and topotecan (T) into new combinations with A. In addition to defining the role of high-intensity chemotherapy in the overall outcome for patients with RAEB-t and RAEB, the authors determined the relative merits of the five regimens (IA, FA, FAI, TA, and CAT), accounting for the nonrandom distribution of the prognostic covariates.

RESULTS

The overall complete response (CR) rate of 58% was significantly associated with karyotype, performance status (PS), treatment in the laminar air flow room, duration of antecedent hematologic disorder and age, but not French-American-British or International Prognostic Scoring System risk categories. Multivariate analysis did not identify statistically significant differences in CR rates obtained with each regimen. Induction death rates increased with age with all but the TA regimen; they were lowest with TA (5.4%) and highest with FAI (20.7%), and these differences were significant in patients older than 65 years. The trend for time to death was the same as for time to recurrence in all groups. Multivariate analysis of time to death identified treatment regimen (FA, FAI, and CAT), cytogenetic status (-5/-7), increasing age, and PS greater than 2 as significant independent unfavorable prognostic factors. After prognostic variables were accounted for, survival with IA treatment remained superior to that of FA and FAI but comparable to TA, and CR duration was only marginally shorter with FA. Landmark analysis showed the overall survival of responders to be superior to that of nonresponders, the difference remaining significant after adjustment for prognostic covariates.

CONCLUSIONS

Although the newer regimens did not improve outcome, TA and CAT produced results comparable to those of IA and may be considered treatment alternatives. The TA regimen was particularly effective in RAEB patients and could be delivered safely, with low induction mortality. Our results indicated that although CR seemed associated with survival advantage, innovative post-remission managements represent a challenge because improvement in outcome is not likely to come from intensified therapy.

Synovial sarcoma in children and adolescents: thirty three years of experience with multimodal therapy

BACKGROUND

Synovial sarcoma (SS) is the most common type of non-rhabdomyosarcoma soft tissue sarcoma in childhood, with controversies about its prognosis and treatment.

PROCEDURE

We reviewed medical records of 42 children and adolescents with SS treated at our institution between 1966 and 1999 to determine treatment results and assess prognostic factors.

RESULTS

With a median follow-up duration of 7.8 years (range 0.2-22.4 years), 5-year progression free survival (PFS) and overall survival (OS) rates were 75.6% (95% Confidence Interval [CI] 62-89.2%) and 87.7% (95% CI 77.3-98.1%) respectively. Eleven patients were dead and four others had progressed but were alive without evidence of disease after further therapy. IRS grouping and tumor invasiveness were found to be significant prognostic indicators (P < 0.01 and = 0.02, respectively). Patients with initial gross total resection (IRS I and II) and non-invasive tumors (T1) were most likely to have prolonged PFS and OS. Patients with small tumors (< 5 cm) (P = 0.09) or with monophasic histology (P = 0.14) had better PFS and OS.

CONCLUSIONS

Achieving a complete resection or gross total resection with microscopic residual disease is vital for survival of patients with localized SS. Patients with localized disease who received radiotherapy had improved local control. Chemotherapy did not seem to impact PFS or OS. Future large multi-institutional trials are needed to address whether post-operative chemotherapy is necessary for patients with localized, surgically removed tumors, whether radiotherapy is necessary for patients with completely resected tumors, and to ascertain the order of importance of all the candidate prognostic markers. Med Pediatr Oncol 2001;37:90-96.

Synovial sarcoma in children: surgical lessons from a single institution and review of the literature

BACKGROUND

Synovial sarcomas are malignant high-grade, soft-tissue neoplasms that account for 7% to 8% of all malignant soft-tissue tumors and are the most common nonrhabdomyosarcoma soft-tissue sarcomas in pediatric patients.

STUDY DESIGN

A retrospective review of the records of children younger than 17 years with synovial sarcoma treated at the University of Texas MD Anderson Cancer Center from 1966 until 1999 was undertaken. Primary site, tumor size, tumor margins, surgical treatment, adjuvant therapy, local and distant recurrence, and survival were recorded for 42 patients. Overall survival (OS) and progression-free survival (PFS) rates were calculated by the Kaplan-Meier method. The PFS and OS comparisons were performed using the log-rank test.

RESULTS

Forty-four patients were identified, but two patients were excluded because of incomplete records. The median followup duration for the 42 patients was 8.8 years (range 0.2 to 22.4 years). The 5-year progression-free survival and overall survival rates were 75.6% and 87.7%, respectively. Eleven patients were dead and four others had progressed but were alive without evidence of disease after further therapy. Intergroup Rhabdomyosarcoma Study (IRS) grouping and tumor invasiveness were found to be significant prognostic indicators (p < 0.01 and p = 0.02, respectively). Patients with initial gross total resection (IRS Groups I and II) and noninvasive tumors (T1) were most likely to have prolonged PFS and OS. Patients with small tumors (<5 cm) (p = 0.09) had better PFS and OS. Adjuvant radiation therapy appeared to be of benefit, and chemotherapy did not seem to impact PFS or OS. Tumors > or = 5 cm are associated with increased risk of local recurrence and distant metastases.

CONCLUSIONS

Complete resection with clear, yet not necessarily large, margins remains the treatment of choice for synovial sarcoma in children. Adjuvant radiation therapy should possibly be considered in patients with clear margins (IRS Group I) and in patients with microscopic residual tumor (IRS Group II). Chemotherapy did not seem to impact PFS or OS. Lymph nodes should be evaluated for local regional disease.

Fluorescence lifetime microscopy of the Na+ indicator Sodium Green in HeLa cells

This study investigates the usefulness of lifetime measurements of Sodium Green for evaluating intracellular Na+ concentration ([Na+]i) in HeLa cells. Frequency-domain lifetime measurements are performed in HeLa cells and in different buffer solutions (with and without K+ and bovine serum albumin). In all cases, the fluorescence decays of Sodium Green are multiexponential, with decay times independent of [Na+]. Three relaxation times are found in the various buffer solutions. Binding of the indicator to albumin results in an increase in the long and intermediate decay times. For Sodium Green inside HeLa cells, the intensity decay can be approximated by a biexponential. The ratio of the fractional intensity of the long decay time (tau2 = 2.4 +/- 0.2 ns) to that of the short component (tau1 = 0.4 +/- 0.1 ns) increases with [Na+]i. The changes in fluorescence decay with [Na+] are significantly less pronounced in cells as compared with the buffer solutions. Similar values for the resting [Na+]i were estimated from lifetime measurements of Sodium Green and from ratiometric measurements using SBFI. Alternatively, [Na+]i can be monitored by measuring only the phase angle at the modulation frequency of 160 MHz. The usefulness of this latter approach is demonstrated by following the changes in [Na+]i induced by reversible inhibition of the Na+/K+ pump.

Fluorescence lifetime microscopy of the sodium indicator sodium-binding benzofuran isophthalate in HeLa cells

The behavior of the sodium indicator sodium-binding benzofuran isophthalate (SBFI) is investigated in HeLa cells by time-resolved fluorescence microscopy. The fluorescence relaxation of SBFI in HeLa cells can be described by a triexponential for intracellular sodium concentration ([Na(+)](i)) between 0 and 90 mM. Changes in [Na(+)](i) affect neither the fluorescence relaxation times (0.21, 0. 60, and 2.7 ns) nor the average decay time (2.2 ns). The preexponential factor of the shortest decay time is negative. However, the ratio of the fluorescence excitation signal at 340 nm to that at 380 nm increases with [Na(+)](i). To elucidate the behavior of SBFI in cells, experiments are performed on SBFI in buffer at various concentrations of sodium, potassium, and bovine serum albumin (BSA) and at various viscosities. The fluorescence decay is triexponential only in the presence of BSA. The relaxation times are independent of [Na(+)] and [BSA]. The preexponential factor of the shortest decay time is negative from a certain [BSA] on, which depends on [Na(+)]. The data indicate that interactions with intracellular components rather than microviscosity influence the SBFI behavior in cells. A model is suggested in which the fluorescence intensities are mainly determined by the signals from the Na(+) subsetSBFI and SBFI subsetprotein complexes.

Membrane potential changes associated with calcium signals in human lymphocytes and rat mast cells

Human lymphocytes and rat mast cells, two non-excitable cellular models, were used to investigate membrane potential changes accompanying Ca2+ signals. Cells were stimulated with agents known to induce both Ca2+ release from internal stores and influx of extracellular Ca2+, namely thapsigargin, ionomycin and compound 48/80. Thapsigargin and ionomycin were used to activate lymphocytes, while compound 48/80 was used to stimulate mast cells. Membrane potential changes and Ca2+ concentration were monitored with the fluorescent dyes bis-oxonol and fura-2, respectively. In lymphocytes, thapsigargin induced a hyperpolarization temporally correlated with the increase in intracellular Ca2+ concentration. This hyperpolarization is due to activation of a K+ conductance which consists of two phases, a first phase independent on external Ca2+ and a second one blocked in a Ca2+-free medium. Ionomycin induced a Ca2+-dependent depolarization attributed to a massive influx of external Ca2+. On the other hand, stimulation of mast cells with compound 48/80 produced a fast hyperpolarization and an increase in intracellular Ca2+ levels. Besides different time-courses, this hyperpolarization differs from that induced by thapsigargin in lymphocytes in two aspects, it is mainly due to a Cl(-)-entry current and exit of K+ and it is completely inhibited in the absence of extracellular Ca2+. Compound 48/80-induced histamine release is not related to membrane potential changes.

The influence of membrane permeability for ions on cell behaviour in an electric alternating field

The behaviour of a cell in an electric alternating field has been investigated, taking into account the field-induced diffusion flows of ions through the membrane. We computed the difference in ion concentration between the internal and external sides of the membrane and the transmembrane diffusion potential induced by the external field. We also studied the effects of these flows on dielectric properties of a tissue in the radio frequency range. The value of the electric permittivity at low frequencies decreases gradually with the increase of membrane permeability for ions, while the electric permittivity at high frequencies is unchanged. These effects are especially important for analysis of the dielectric spectrum of a tissue or cell suspension which has undergone the influence of various physical or chemical agents, e.g. ionizing radiation or detergents.