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Biomedical subjects

J H Li

Publications and source records attributed to J H Li.

At least 163 records · Page 9Linked to original sources
PubMed1985

Capacity of small B cell-enriched populations to stimulate mixed lymphocyte reactions: marked differences between irradiated vs. mitomycin C-treated stimulators.

To investigate whether small B cells can stimulate mixed lymphocyte reactions (MLR), highly purified populations of large vs. small B cell fractions were tested for their capacity to evoke MLR across Mls vs. H-2 barriers. Large B cell fractions stimulated high MLR to Mls and H-2 determinants, irrespective of whether the stimulators were exposed to irradiation or pretreated with mitomycin C. In accord with the findings of others, irradiated small B cell fractions proved to be very poor stimulators of MLR. Significantly, however, mitomycin C-treated small B cell fractions elicited high MLR, particularly to Mls determinants. The finding that small B cell fractions treated with irradiation are poor stimulators of T cells correlates with the known radiosensitivity of B cells. In this respect, the widely held view that small B cells do not have antigen-presenting cell (APC) function rests largely on studies with irradiated B cells. The present finding that T cells respond well to small B cells treated with mitomycin C, however, indicates that small B cell fractions do have APC function. Whether the APC function of small B cells reflects a response to resting B cells per se rather than to cells undergoing activation in vitro, however, remains to be ascertained.

Animals↗
PubMed1985

Hematoporphyrin derivative and laser photodynamical reaction in the diagnosis and treatment of malignant tumors.

This paper reports the use of hematoporphyrin derivative (HpD) with laser activation in China for the diagnosis and treatment of various kinds of malignant neoplasms. Fluorescence observation for diagnosis was performed for 170 tumors. One hundred and fifty-one (88.8%) fluoresced visably upon excitation with either argon or He-Cd laser light. One hundred and thirty-nine malignant tumors in 136 patients were treated by this method. The percentage of all tumors responding to treatment was 80.6%. Partial to complete response were obtained in 51.1% of the tumors treated. The advantages and disadvantages of this method are discussed. It was found effective in treating various kinds of neoplasms located at different anatomical sites. The penetrating depth of the laser is shallow. This limits its effect and application. A search for new photosensitizing drugs and an increase in the penetrating depth of laser irradiation are urgent goals for further development of this technique.

Antineoplastic Agents↗
PubMed1985

Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: I. Pyrazine-ring modifications.

The overall on- and off-rate constants for blocking epithelial Na channels by amiloride analogs were estimated by noise analysis of frog skin epithelium. The substituents at position-5 and -6 of the pyrazine ring of amiloride were varied in order to obtain the structure/rate constant relationship. (1) The off-rate constant increases with halo-substitutions at position-6 in the order Cl less than Br less than l less than F less than H. Substitution of Cl by H lowers the standard free energy of activation of the off-step by 2.3 kcal mol-1. The on-rate constant is not affected. Apparently the substituent at ring position-6 controls the duration of attachment in the blocking position. pKa considerations show that the duration is longer when the 6-substituent is more negatively polarized. We suggest that this substituent binds to the receptor by virtue of its electronegativity. (2) In contrast, replacement of the adjacent 5-amino group (electron donor) by H or Cl affects both the on-rate and the off-rate. The dual effect may be explained by a decrease of the electronic charge at more remote parts of the molecule (on-rate decrease), as well as at the 6-position (off-rate increase). Apparently the 5-amino group stabilizes the blocking position by increasing the electron density on the 6-ligand.

Amiloride↗
PubMed1984

Application of hematoporphyrin derivative and laser-induced photodynamical reaction in the treatment of lung cancer: a preliminary report on 21 cases.

This paper reports results of hematoporphyrin derivative based on photodynamic therapy (PDT) of 24 lung cancer lesions in 21 patients that were followed at least three months. Three of 24 lesions exhibited complete remission and 20 of 24 lesions exhibited a response to PDT. Tumors in twenty of twenty-one patients exhibited visually discernible hematoporphyrin derivative fluorescence upon irradiation with the 514-nm line from an argon ion laser. There were no severe complications due to PDT. The hematoporphyrin derivative, argon iin laser pumped dye laser (rhodamine B) system,and quartz fiber we used in this clinical series were all made in the People's Republic of China.

Adenocarcinoma↗
PubMed1983

Competitive blocking of epithelial sodium channels by organic cations: the relationship between macroscopic and microscopic inhibition constants.

Fluctuation analysis of Na current passing the apical membrane in the skin of Rana ridibunda was used to study the kinetics of Na-channel blocking by several organic cations present in the outer solution together with 60 mM Na. The ratios of the apparent off-rate and on-rate constants (the microscopic inhibition constants) thus obtained for triamterene, triaminopyrimidine (TAP), 5,6-diCl-amiloride, 5H-amiloride and amiloride itself are found to be in the mean about sevenfold smaller than the corresponding inhibition constants obtained from macroscopic dose-response curves. The apparent discrepancy is explicable by competition of the organic blocker with the channel block by Na ions (the self-inhibition effect). The type of interaction between extrinsic blockage and self-inhibition may be purely competitive or mixed. However, in case of mixed inhibition the competitive component must dominate the noncompetitive component by at least seven to one.

Amiloride↗
PubMed1983

Chemical stimulation of Na transport through amiloride-blockable channels of frog skin epithelium.

The stimulation of apical Na permeability caused by a number of reagents effective from the outer side of the membrane was investigated by fluctuation analysis. In the epidermis of R. ridibunda, parachloromercuriphenyl sulfonate (PCMPS) and benzimidazolyl guanidine (BIG) increase the number (N0) of conducting Na channels by releasing channels from Na self-inhibition. As a consequence, the apparent macroscopic affinity for amiloride is increased. 5-dimethyl amiloride and trinitrobenzene sulfonate (TNBS) also cause reversible stimulation by increasing N0; here release from self-inhibition is less clear. With each of the four stimulators investigated, the Na channel current remained unaffected or was only marginally increased. In addition to its stimulatory effect, TNBS caused irreversible blockage of Na channels. Apart from their stimulatory effects, BIG and 5-dimethyl amiloride, both of which have a side-chain terminated with an amidino group, are high rate-blocking competitors of amiloride.

4-Chloromercuribenzenesulfonate↗
PubMed1982

The role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormone.

Urinary bladders of Bufo marinus were depolarized, by raising the serosal K concentration, to facilitate voltage-clamping of the apical membrane. Passive Na transport across the apical membrane was then studied with near-instantaneous current-voltage curves obtained before and after eliciting a natriferic response with oxytocin. Fitting with the constant-field equation showed that the natriferic effect is accounted for by an increase in the apical Na permeability. It is accompanied by a small increase in cellular Na activity. Furthermore, fluctuation analysis of the amiloride-induced shot-noise component of the short-circuit current indicated that the permeability increase is not due to increased Na translocation through those Na channels which were already conducting prior to hormonal stimulation. Rather, the natriferic effects is found to be based on an increase in the population of transporting channels. It appears that, in response to the hormone, Na channels are rapidly "recruited" from a pool of electrically silent channels.

Animals↗