Biomedical subjects

Tim J C Jacob

Publications and source records attributed to Tim J C Jacob.

4 recordsLinked to original sources

PubMed2002

pH-Dependent channel activity of heterologously-expressed main intrinsic protein (MIP) from rat lens.

Wild-type rat lens main intrinsic protein (MIP) was heterologously expressed in the membrane of Spodoptera frugiperda (Sf21) cells using the baculovirus expression system and in mouse erythroid leukaemia cells (MEL C88). Both MEL and Sf21 cell lines expressing wild-type MIP were investigated for the conductance of ions using a whole cell patch clamp technique. An increase in conductance was seen in both expression systems, particularly on lowering the pH to 6.3. In Sf21 cells, addition of antibodies to the NPA1 box resulted in a reduction of current flow. These results suggest that MIP has pH-dependent ion channel activity, which involves the NPA1 box domain.

Animals↗

PubMed2002

Regulatory volume decrease is actively modulated during the cell cycle.

Nasopharyngeal carcinoma cells, CNE-2Z, when swollen by 47% hypotonic solution, exhibited a regulatory volume decrease (RVD). The RVD was inhibited by extracellular applications of the chloride channel blockers tamoxifen (30 microM; 61% inhibition), 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 100 microM; 60% inhibition), and ATP (10 mM; 91% inhibition). The level and time constant of RVD varied greatly between cells. Most cells conducted an incomplete RVD, but a few had the ability to recover their volume completely. There was no obvious correlation between cell volume and RVD capacity. Flow cytometric analysis showed that highly synchronous cells were obtained by the mitotic shake-off technique and that the cells progressed through the cell cycle synchronously when incubated in culture medium. Combined application of DNA synthesis inhibitors, thymidine and hydroxyurea arrested cells at the G1/S boundary and 87% of the cells reached S phase 4 h after being released. RVD capacity changed significantly during the cell cycle progression in cells synchronized by shake-off technique. RVD capacity being at its highest in G1 phase and lowest in S phase. The RVD capacity in G1 (shake-off cells sampled after 4 h of incubation), S (obtained by chemical arrest), and M cells (selected under microscope) was 73, 33, and 58%, respectively, and the time constants were 435, 769, and 2,000 sec, respectively. We conclude that RVD capacity is actively modulated in the cell cycle and RVD may play an important role in cell cycle progress.

Adenosine Triphosphate↗

PubMed2002

The correlation between physiological and psychological responses to odour stimulation in human subjects.

OBJECTIVES: To correlate physiological and psychological responses to odour stimulation. METHODS: Olfactory event-related potentials (OERP) were recorded from human subjects in response to different odour pulse protocols. Pulse duration and interstimulus interval (ISI) were varied while the subjects recorded pulse detection by a button press. RESULTS: There was a correlation between odour strength and OERP. The amplitude of the OERP (peak positive-peak negative) declined by 48% with repetitive stimulation for all stimulus strengths. The time constant for this decline (adaptation) was concentration dependent and varied from 10 to 4 s for increasing odorant strength (from 35 to 200 ms pulse of saturated amyl acetate vapour diluted 1:3 at 3 l min(-1) at 24 degrees C). The psychometric test score (cognitive odour perception) was also concentration dependent and increased with increasing stimulus strength at all ISIs except the lowest value; 2.5 s. At this ISI adaptation/habituation interfered with the dose-response. The decline of the psychometric test score with increasing stimulus frequency (decreasing ISI) was more rapid (tau approximately 2.5 s) than that of the OERP. The psychometric test score declined to zero at a constant rate and was not dependent upon stimulus strength. CONCLUSIONS: Continuous olfactory stimulation results in a shut-down of cognitive perception with a time constant of around 2.5 s while the response of the physiological system (receptors, transduction and relay system) declines by about 50% with a slower time course (> or = 4 s). This former process defines habituation in the olfactory system while the latter describes adaptation. Since the adaptation process is concentration dependent the rate of adaptation contains information about odour strength, thus both the amplitude of the OERP and the rate of adaptation could encode stimulus strength.

Adaptation, Physiological↗

PubMed2002

Cell cycle-dependent expression of volume-activated chloride currents in nasopharyngeal carcinoma cells.

Patch-clamping and cell image analysis techniques were used to study the expression of the volume-activated Cl(-) current, I(Cl(vol)), and regulatory volume decrease (RVD) capacity in the cell cycle in nasopharyngeal carcinoma cells (CNE-2Z). Hypotonic challenge caused CNE-2Z cells to swell and activated a Cl(-) current with a linear conductance, negligible time-dependent inactivation, and a reversal potential close to the Cl(-) equilibrium potential. The sequence of anion permeability was I(-) > Br(-) > Cl(-) > gluconate. The Cl(-) channel blockers tamoxifen, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), and ATP inhibited I(Cl(vol)). Synchronous cultures of cells were obtained by the mitotic shake-off technique and by a double chemical-block (thymidine and hydroxyurea) technique. The expression of I(Cl(vol)) was cell cycle dependent, being high in G(1) phase, downregulated in S phase, but increasing again in M phase. Hypotonic solution activated RVD, which was cell cycle dependent and inhibited by the Cl(-) channel blockers NPPB, tamoxifen, and ATP. The expression of I(Cl(vol)) was closely correlated with the RVD capacity in the cell cycle, suggesting a functional relationship. Inhibition of I(Cl(vol)) by NPPB (100 microM) arrested cells in G(0)/G(1). The data also suggest that expression of I(Cl(vol)) and RVD capacity are actively modulated during the cell cycle. The volume-activated Cl(-) current associated with RVD may therefore play an important role during the cell cycle progress.

Adenosine Triphosphate↗