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Biomedical subjects

S Lahiri

Publications and source records attributed to S Lahiri.

At least 91 records · Page 5Linked to original sources
PubMed1995

Some aspects of the causes of enhanced immune response of in vitro frozen ascites fibrosarcoma tumor cells in mice.

Estimation of 3 M KCl-extracted ascites fibrosarcoma (AFS) tumor cell membrane peripheral proteins in native and frozen tumor cells showed approximately a three-, four-, and fivefold increase per 1 x 10(6) cells of single-, three-, and programmed three-cycle frozen AFS tumor cells, respectively, compared to the same number of native cells, indicating an increase in surface membrane protein concentration with freezing. The 10% gel (homogeneous) electrophoretic (SDS-PAGE) study of 3 M KCl-extracted native and frozen cell membrane proteins showed (i) membrane proteins of native cells resolve into many more components compared to those of any frozen membranes, i.e., single, three, and programmed three cycle, the components decreasing in that order; (ii) the concentration of larger-molecular-weight protein fractions (> or = 75 kDa) decreases while those of smaller fractions (14 to 24 kDa) increase in frozen cells, with the maximum being in the programmed three-cycle frozen group. In contrast, the native cell membrane is rich in higher-molecular-weight proteins (> or = 75 kDa) with concentrations slowly decreasing toward lower-molecular weight fractions. Thus, the probable reasons for increased immune response of animals immunized with frozen AFS tumor cells are (i) absolute increase in cell surface protein concentrations as given by 3 M KCl extraction of cell membrane peripheral protein estimation in AFS tumor cells postfreeze; (ii) cell-surface protein pattern which is heterogeneous before freezing becomes relatively more homogeneous following freezing of AFS tumor cells; and (iii) depolymerization and breaking of higher-molecular-weight components which increase the concentration of terminal-sequence antigenic determinants and increase accessibility of determinant grouping by removing steric hindrance following freezing.

Animals↗
PubMed1995

Effect of UV-B (302 nm) irradiation on isolated rat hepatocytes.

The present study aimed to evaluate the effect of UV-B irradiation on the functional integrity, and the metabolic and detoxifying capacity of isolated rat hepatocytes. Isolated rat hepatocytes were irradiated in various doses (400 Jm-2, 600 Jm-2, 800 Jm-2 and 1000 Jm-2). The cells were assayed for total lactate dehydrogenase, Na(+)-K(+)-ATPase, ornithine carbamyltransferase activity (OCT) and urea production capacity. Lactate dehydrogenase and Na(+)-K(+)-ATPase activity were significantly decreased in all four irradiated groups (P < 0.001), whereas viability, OCT and urea production capacity showed no alterations.

Animals↗
PubMed1995

Electrochemical detection of rapid DA release kinetics during hypoxia in perfused-superfused cat CB.

The hypothesis that hypoxic excitation is coupled to dopamine (DA) secretion was tested in perfused-superfused cat carotid bodies (CB). DA was electrochemically detected by an amperometric method (constant applied potential +150 mV) with Nafion polymer-coated recessed gold microsensors (tip diameter 3-8 microns) in 10 cat CBs. Neural discharge (ND) from the whole sinus nerve was measured simultaneously with DA changes during interruption of perfusate flow and during hypoxic perfusion (5% O2). A computer-controlled instrument using a chronoamperometric technique (+550-mV pulses) with a Nafion-coated carbon fiber microelectrode (tip diameter 35 microns) was used to detect DA changes in two CBs during similar hypoxic stimuli. Rapid DA release kinetics were measured during flow interruption with an initial rate of 1.05 +/- 0.15 (SE) microM/s within the first 10-15 s. At most measurement sites, the increase in DA preceded the rise in ND. After the initial increase, DA release slowed to 0.16 +/- 0.02 microM/s, reaching a maximum DA concentration of 20.7 +/- 2.6 microM above baseline after 90 s of flow interruption. Nicotine (10-micrograms bolus) caused a large increase in ND without a proportional increase in DA release. Spatially detailed time-resolved electrochemical measurements were able to discriminate between DA release during hypoxia and chemoexcitatory responses that do not involve DA release.

Animals↗
PubMed1995

Effect of hypoxia on intracellular pH of glomus cells cultured from cat and rat carotid bodies.

To test the hypothesis that hypoxia may induce cellular acidification during chemotransduction in the carotid body, we compared the effects of hypoxia and of extracellular acidosis on intracellular pH (pHi) of glomus cells cultured from rat and cat carotid bodies. The cells were prepared and cultured for 2-7 days. The plated cells were loaded with a pH-sensitive fluorescent probe, SNARF-1-acetoxymethyl ester, and were placed in a closed chamber and superfused. The effects of lowering PO2 and pH in the superfusion medium containing CO2-HCO3- buffer on the glomus cell pHi were measured at 37 degrees C. The pHi was measured in a single or a few isolated cells with single excitation at 540 nm and dual emission at 590 and 640 nm, after the exposure to different PO2 levels from 132 to 43, 14, and 1-2 Torr for 10-12 min in the closed chamber. The resting pHi values were 7.263 +/- 0.008 for rat and 7.175 +/- 0.004 for cat carotid body glomus cells. For a decrease of PO2 from 132 Torr to 14 Torr, the change in pHi values, on average, for cat and rat glomus cells was 0.034 lower, and with PO2 decrease to 1-2 Torr for the cat glomus cells, the change in pHi values was 0.051 lower. On the other hand, when the perfusate pH values were decreased from 7.4 to 6.9 during normoxia, the reduction of change in pHi values were 0.327 for the rat and 0.397 for the cat. Thus glomus cell pHi change due to low PO2 exposure was not significant and was not commensurate with the large increases in the chemosensory activity.

Acidosis, Lactic↗
PubMed1995

Survivability and leucocyte migration inhibition in mice immunized with cryotreated ascites fibrosarcoma cells using different freeze-thaw cycles.

Attempts have been made to assess as to what extent in vitro assay of cellular immunity, e.g. leucocyte migration inhibition (LMI) in mice immunized with different freeze-thaw cycles could reflect host resistance in vivo. While survivability of animals improved significantly by immunization with single cycle (P < 0.05) to three cycle (P < 0.001) and programmed three cycle (P < 0.001) cryo-treated tumor cells compared to controls, the percentage LMI in the same groups of animals decreased progressively. The KCl(3M) extracted tumor cell protein (antigen) of both viable and cryo-treated cells showed a progressively increased protein concentrations per 1 x 10(6) tumor cells with viable cells being least and programmed three cycle cryo-treated cells highest. The apparent discrepancy observed between percentage migration inhibition and survivability may be due to the fact that (1) survivability is a function of body's total immune response while LMI represents the response of one effector limb only; (2) immuno-regulatory mechanisms depend on a balance between activation and suppression and suppressor cells being more sensitive and of shorter life span, affect migration inhibition but not the survivability; (3) cryo-treatment alters tumor cell surface antigen affecting immunological balance; and (4) suppressor and antitumor activities against antigenic stimulation develop simultaneously in different organs and LMI performed with sensitized splenic cells, where, perhaps, suppressor cell activity dominates.

Animals↗
PubMed1994

The primary oxygen sensor of the cat carotid body is cytochrome a3 of the mitochondrial respiratory chain.

Carbon monoxide was shown to be competitive with O2 in oxygen sensing by perfused carotid bodies isolated from cats, afferent electrical activity increasing with either decreasing O2 or increasing CO. The CO-induced increase in afferent activity was fully reversed by bright light. At submaximal light intensities the extent of reversal, after correcting to equal light intensity of light quanta at each wavelength, was maximal for light of 432 +/- 2 and 590 +/- 2 nm, with a ratio (432/590) of approximately 6. This spectrum is characteristic of the CO compound of mitochondrial cytochrome a3. The photo-reversible inhibition of oxygen sensing activity by CO accounts for at least 80% of the oxygen chemosensory activity of the carotid body.

Animals↗
PubMed1994

TSH receptor gene expression in retroocular fibroblasts.

RNA was isolated from fibroblasts from the retroocular area, from endomysial fibroblasts obtained from orbital lateral rectus muscle, and from abdominal skin fibroblasts. The RNA was reverse transcribed into cDNA which was then used as a template for PCR with primers encompassing a portion (nucleotides 989-1235) of the extra-cellular domain of the human TSH receptor (hTSH-R). A definite 247 BP product was detected from fibroblast RNA by ethidium bromide staining, and was confirmed by hybridization with labelled hTSH-R cDNA. The product had homology with the known TSH-R cDNA. These studies indicate that human fibroblasts can express hTSH-R, and they suggest that a cross reactive immunologic response between anti-hTSH-R and these fibroblast TSH receptors may play a role in the genesis of Graves' ophthalmopathy.

Base Sequence↗
PubMed1994

Chronic hyperoxic effects on cat carotid body catecholamines and structure.

To account for the loss of O2 chemoreception in the cat carotid body during chronic hyperoxia, we studied the putative neurotransmitter correlates. Also, we studied the structural aspect of the carotid body tissues. We found that catecholamine concentrations increased and that the densecored vesicles in the glomus cells were not depleted, indicating that a lack of transmitters was not the cause for the loss of O2 chemoreception.

Animals↗
PubMed1994

Nitric oxide-related inhibition of carotid chemosensory nerve activity in the cat.

The hypothesis that endogenous nitric oxide may play a physiological role in the regulation of carotid chemosensory activity was tested in this study. The nitric oxide synthase (NOS) inhibitors, L-nitro-arginine-methyl ester (L-NAME, 25-200 microM) and NG-monomethyl-L-arginine acetate (L-NMMA, 50 and 100 microM) were used to study its effects on the chemosensory activity of perfused and superfused cat carotid bodies (n = 21) in vitro at 37-37 degrees C. L-NAME elicited slow excitation of the sensory activity as did L-NMMA. The peak-response was dose-dependent, and approached saturation around 200 microM. The excitation by L-NAME showed the following characteristics (mean +/- SEM): latency of response, 2.2 min +/- 0.3 min; time to peak response, 5.5 min +/- 1.0 min and the peak response increased to 407 +/- 42 imp/sec from 88 +/- 13 imp/sec. The peak response was significantly different (P < 0.05) from the baseline activity. L-arginine (50-500 microM) only briefly reversed the stimulation. Hypoxia enhanced the excitation by L-NAME. On the other hand, sodium nitroprusside (SNP, 0.5-10 microM) which supplies NO, terminated the excitatory effect of L-NAME. The results provide evidence in favor of an inhibitory role of endogenous NO in the carotid body, and exogenous application of NO confirms the inhibitory effect.

Amino Acid Oxidoreductases↗
PubMed1994

Testing the metabolic hypothesis of O2 chemoreception in the cat carotid body in vitro.

It is known that oligomycin reduces the oxidative phosphorylation high-energy state or high-energy intermediates by inhibiting the formation of ATP without directly inhibiting electron transport, whereas metabolic uncouplers dissipate the high-energy state without net production of ATP. The metabolic hypothesis for O2 chemoreception in the carotid body (CB) predicts that 1) oligomycin should diminish O2 consumption and attenuate O2 chemoreception and 2) uncouplers should reverse the effect of oligomycin by increasing O2 consumption without restoring O2 chemoreception. These predictions were tested by simultaneously measuring CB chemosensory discharge from the sinus nerve and the rate of tissue O2 disappearance (dPO2/dt) during interruption of perfusate flow in perfused-superfused cat CB preparations (n = 9). O2 consumption was calculated from dPO2/dt. Flow-interruption responses were measured before and after oligomycin (1-microgram bolus) and subsequently after dinitrophenol (50 microM). Chemosensory responses to bolus injections of hypercapnic Tyrode solution, cyanide, or nicotine were also tested periodically. Oligomycin diminished dPO2/dt from -2.67 +/- 0.30 to -2.02 +/- 0.19 (SE) Torr/s (P < 0.004, paired t test) and reduced the maximal sensory response from 196 +/- 43 to 124 +/- 12 impulses/s (P < 0.002, paired t test) while augmenting the initial response to CO2. Dinitrophenol reversed the metabolic depressant effect of oligomycin but further suppressed the chemosensory response. These results confirm the above predictions and strengthen the metabolic hypothesis for O2 chemoreception in the CB.

2,4-Dinitrophenol↗