Potassium currents in cultured rabbit retinal pigment epithelial cells

Membrane potential and ionic currents were studied in cultured rabbit retinal pigment epithelial (RPE) cells using whole-cell patch clamp and perforated-patch recording techniques. RPE cells exhibited both outward and inward voltage-dependent currents and had a mean membrane capacitance of 26 +/- 12 pF (SD, n = 92). The resting membrane potential averaged -31 +/- 15 mV (n = 37), but it was as high as -60 mV in some cells. When K+ was the principal cation in the recording electrode, depolarization-activated outward currents were apparent in 91% of cells studied. Tail current analysis revealed that the outward currents were primarily K+ selective. The most frequently observed outward K+ current was a voltage- and time-dependent outward current (IK) which resembled the delayed rectifier K+ current described in other cells. IK was blocked by tetraethylammonium ions (TEA) and barium (Ba2+) and reduced by 4-aminopyridine (4-AP). In a few cells (3-4%), depolarization to -50 mV or more negative potentials evoked an outwardly rectifying K+ current (IKt) which showed more rapid inactivation at depolarized potentials. Inwardly rectifying K+ current (IKI) was also present in 41% of cells. IKI was blocked by extracellular Ba2+ or Cs+ and exhibited time-dependent decay, due to Na+ blockade, at negative potentials. We conclude that cultured rabbit RPE cells exhibit at least three voltage-dependent K+ currents. The K+ conductances reported here may provide conductive pathways important in maintaining ion and fluid homeostasis in the subretinal space.

Improved double immunohistochemical staining method for cryostat and paraffin wax sections, combining alkaline phosphatase anti-alkaline phosphatase and indirect immunofluorescence

AIMS

To develop and immunohistochemical staining method for cryostat and paraffin wax sections so that two different antigens in the same section of tissues could be detected by combining immunoenzyme and immunofluorescence techniques.

METHODS

This double immunohistochemical staining method combines alkaline phosphatase-anti-alkaline phosphatase (APAAP) using New Fuchsin as a chromogen and indirect immunofluorescence.

RESULTS

APAAP staining for one antigen of this double immunohistochemical staining method was observed under bright field conditions alternating with immunofluorescence for another antigen under ultraviolet light. The double exposed photograph of both easily identified the two signals within the same cell.

CONCLUSIONS

This double immunohistochemical staining method can overcome the disadvantages of any masking effect of the double immunoenzymatic methods and the background problems of double immunofluorescence method especially when applied to paraffin wax sections. It also permits good morphological identification of the doubly stained cells which may be of crucial importance in studies on pathology specimens.

Epstein-Barr virus (EBV)-related lymphoproliferative disorder with subsequent EBV-negative T-cell lymphoma

A 58-year-old Chinese man presented initially with generalized lymphadenopathy, and lymph-node biopsy showed disturbed architecture with preponderance of large B-blasts mixed with numerous CD8+ T lymphocytes, consistent with an acute Epstein-Barr virus (EBV) infection. Immunohistological and gene rearrangement studies confirmed the absence of clonal T or B cells. Polyclonal EBV with lytic infection was detected by Southern blot hybridization (SoBH). Expression of EBV proteins (EBNA2, LMP and ZEBRA) was detected in a proportion of cells by immunostaining. EBV-lytic proteins EA-D, VCA, MA were also detected in rare scattered cells. Double immunostaining showed that the LMP-positive cells were of B and of T phenotype: 73% CD19+, 26% CD2+, 23% CD3+, 8% CD4+, 17% CD8+. After biopsy, there was spontaneous regression of lymph-node enlargement, but lymphadenopathy recurred 8 months later, and the second lymph-node biopsy showed T-cell lymphoma, confirmed by detection of clonally rearranged T-cell-receptor beta-chain gene. However, EBV genome could not be detected in the second biopsy by SoBH, in situ hybridization for EBV-encoded EBER RNA, and immunostaining for EBNA2, LMP and ZEBRA was also negative. This case is of special interest because an EBV-negative T-cell lymphoma developed shortly after an acute episode of EBV-related lymphoproliferation, even though many EBV-positive T cells were detected during the acute episode. EBV was apparently not a direct cause of the lymphoma, but the close temporal association of the 2 lesions supports the hypothesis that EBV can act as a co-factor in lymphomagenesis.

Lack of correlation between expression of Epstein-Barr virus (EBV) latent membrane protein and bcl-2 oncoprotein in vivo

AIMS

To evaluate whether there is any correlation between the expression of Epstein-Barr virus (EBV) latent membrane protein (LMP) and oncoprotein bcl-2 in the lymph node biopsy specimens of a Chinese patient with EBV-related reactive lymphoproliferation who later developed T cell lymphoma after a short period of time.

METHODS

Immunohistochemistry, with a standard alkaline phosphatase antialkaline phosphatase (APAAP) method and New Fuchsin as a chromogen, was used for single staining of bcl-2 or LMP. Double immunostaining combining APAAP and indirect immunofluorescence was performed for dual labelling of LMP and bcl-2.

RESULTS

bcl-2 was expressed in 10-30% of cells in the first lymph node biopsy specimen (EBV-associated lymphoproliferative disorder) and 30-50% of cells in the second lymph node biopsy specimen (T cell lymphoma). LMP was expressed in the first biopsy specimen but not in the second. Double immunostaining results showed that around 78% of LMP positive cells were bcl-2 negative and 94% bcl-2 positive cells were LMP negative. Among the very small fraction of LMP and bcl-2 double positive cells, the intensity of bcl-2 staining was heterogeneous and was not always stronger than that observed in LMP negative bcl-2 positive cells.

CONCLUSIONS

The expression of bcl-2 protein is independent of LMP protein status in vivo. Several mechanisms may be involved in EBV associated lymphomagenesis, and bcl-2 induction may occur independently of LMP expression.

Molecular cloning and expression of a delta-opioid receptor from rat brain

We have isolated and characterized a rat delta-opioid receptor. The deduced amino acid sequence (372 aa) closely resembles the murine delta-opioid receptor, DOR-1. In fact, 97% of the amino acid residues are conserved between the two species, while 93% of the nucleic acid residues are identical. A 6 kb mRNA was detected in rat cortex using rat DOR-1 as a probe. When expressed in COS cells, the clone shows high-affinity opioid binding with selectivity for delta-opioids. The rat delta-opioid receptor cDNA clone will be a useful tool for studying the function of delta-opioid receptor in rats.

[Homology of Chinese, Japanese, and American strains of hepatitis C virus]

As we know, the main HCV strain in Japan (HCV-J 4) is highly diverse in sequence from the original American strain (HCV-US). By comparing the sequences of these two strains, a region, located in the 3'-terminus of the putative E gene in HCV genome, was selected for PCR amplification. In this region, the Japanese strain showed high diversity from the American strain. From 4 patients, 8 isolates with the length of 277 bp, were cloned and sequenced. The homology of these 8 clones was high, indicating that these clones were in the same strain. This strain might be the major strain in China, named HCV-CHN1 in this paper. Since there were still many varieties in these 8 clones, HCV CHN1 could be possibly divided into 3 substrains. HCV-CHN1 was also found to be similar to HCV-J 4, with nucleotide homology of 83.4-86.3%, and amino acid homology of 78.3-88.0%, but remote from HCV-US, with homologies of only 68.6-72.6% and 69.6-73.9%, respectively. These results might be of paramount significance in developing the detection method for HCV infection and in preparing HCV vaccine.

[Function of direct repeat sequences in DNA replication of hepatitis B virus]

In order to investigate the function of the direct repeat sequences (DR 1 and DR 2) in DNA replication of hepatitis B virus (HBV), the nucleotides in DR 1 and/or DR 2 were substituted by oligonucleotide site-directed mutagenesis. HepG 2 cells were transfected with tandem dimers of the mutants. The results indicate that (1) DR 1 is responsible for the synthesis of pregenome RNA or minus strand DNA. (2) The relative homogeneity between DR 2 and DR 2 is very important in the formation of long cohesive end region and the circulization of HBV DNA. (3) It is first reported that in natural infection HBV DNA has a defective replication route. It gives a 3.2 Kb linear form double strand DNA with uniform structure.