Tissue-specific granularity of gap junction cytoplasmic surfaces revealed by rapid-freeze, deep-etch replicas

RT-PCR study of the distribution of connexin 43 mRNA in the glomerulus and renal tubular segments

An RT-PCR study of the distribution of connexin 43 (Cx43) mRNA in glomeruli and along the rat tubular segments was carried out to establish the differential expression of Cx43 in the different segments of the tubule, in renal regions, in isolated glomerular preparations (IGP), and in microdissected glomeruli. The mRNA level of Cx43 in macrodissected renal regions appeared in the following order: inner papilla > outer papilla and IGP > outer medulla and cortex. Among the microdissected tubules, inner medullary collecting ducts (IMCD) expressed the highest level of Cx43 mRNA, followed by the cortical collecting ducts (CCD). The proximal convoluted tubules and proximal straight tubules expressed significantly less Cx43 than the IMCD, glomeruli, and CCD. Medullary thick ascending limb and distal convoluted tubules showed the lowest level of Cx43 mRNA. The RT-PCR results of the microdissected segments correlate well with those obtained by RT-PCR of the renal regions. The high concentration of Cx43 mRNA in the IMCD together with the observation of abundant punctate immunofluorescence for Cx43 suggests that the IMCD not only expresses Cx43 mRNA but also that the mRNA is translated to Cx43 protein.

Freeze-fracture and immunohistochemical studies of gap junctions in human gastric mucosa with special reference to their relationship to gastric ulcer and gastric carcinoma

Our aim was to determine whether the development of gap junctions in the human gastric mucosa has any relation to gastric ulcer and gastric carcinoma. Freeze-fracture replicas were prepared from the endoscopic biopsy specimens of 20 patients with gastric ulcer and 7 healthy volunteers. Large fractured areas of lateral cell membranes of surface mucous cells were examined randomly under an electron microscope. Small gap junctions were observed between gastric surface mucous cells in all healthy volunteers. Gap junctions in the patients with gastric ulcer were significantly fewer than in the healthy volunteers. In addition, gap junctions in patients with recurrent ulcer were significantly fewer than in those with first-onset ulcer. There was no obvious relationship between age and the development of gap junctions in patients with gastric ulcer or in healthy volunteers. In the areas of intestinal metaplasia, gap junctions were occasionally seen between absorptive cells of the villi, but not in the lateral membranes of goblet cells. Fresh frozen sections for indirect immunofluorescence were prepared from the endoscopic biopsy specimens of 19 patients with gastric ulcer and 5 patients with gastric cancer. Monoclonal antibody against liver gap junction protein (anti-connexin 32, 6-3G11) was used for the indirect immunofluorescence. On the border of gastric ulcer, fluorescent spots in the surface mucous cells were significantly fewer than in the surface mucous cells of the body and antrum which were distant from the ulcer area in the same patients. In gastric cancer tissue specimens, fluorescent spots were not observed at all.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine-stimulated changes of membrane potential and intracellular Ca2+ concentration recorded in endothelial cells in situ in the isolated rat aorta

The intracellular free Ca2+ concentration and membrane potential changes evoked by acetylcholine were recorded from whole-cell patch-clamped endothelial cells in situ in the isolated rat aorta. The endothelium had a resting membrane potential of -52 +/- 3 mV (SEM, range -35 mV to -76 mV n = 34) and a low input resistance (32 - 54 M omega). The membrane potential hyperpolarised by 3-30 mV on continuous application of acetylcholine at concentrations that produced endothelium-dependent relaxations in isolated rat aortic rings (range 1-500 nM). The response often comprised complex fluctuations of hyperpolarised membrane potential. Calcium concentration was measured with the fluorescent indicator furaptra, which has a wide range and minimises Ca2+ buffering. Acetylcholine evoked an initial rapid elevation of intracellular Ca2+ concentration, peaking in the range 6-35 microM, which declined with a half time of approximately 6 s, followed by repetitive [Ca2+] spikes of amplitude 2-18 microM in 23 of 34 cells. The initial [Ca2+] transient and hyperpolarisation were unaffected by removal of external Ca2+, whilst subsequent [Ca2+] spikes and maintained hyperpolarisations required the presence of external Ca2+. Both the hyperpolarisation and Ca2+ responses elicited by acetylcholine were abolished by atropine (1 microM). These results show that endothelial cells in situ exhibit large, fast repetitive [Ca2+] spikes in response to extracellular acetylcholine.

Electron microscopic study of intercellular junctions in human gastric mucosa with special reference to their relationship to gastric ulcer

The development of gap junctions in the human gastric mucosa has been examined to see if there is any relation to gastric ulcer. Freeze fracture replicas were prepared from the endoscopic biopsy specimens of 20 patients with gastric ulcer (15 men and five women, aged 49 (13) years) and seven healthy volunteers (four men and three women, aged 41 (19) years). Large fractured areas of lateral cell membranes of surface mucous cells were observed randomly at a direct magnification of 15,000 using electron microscopy. Small gap junctions were observed between gastric surface mucous cells in all healthy volunteers. Gap junctions in the patients with gastric ulcer were significantly fewer than in the healthy volunteers. In addition, gap junctions in patients with recurrent ulcer were significantly fewer than in those with first onset ulcer. There was no obvious relationship between age and the development of gap junctions in patients with gastric ulcer or in healthy volunteers. In areas of intestinal metaplasia, gap junctions were occasionally seen between absorptive cells of the villi, but not in the lateral membranes of goblet cells. These findings suggest that loss of intercellular communication via gap junctions is associated with gastric ulcer formation.

Internalized gap junctions in ciliary epithelium of rabbit and rat. A transmission electron-microscopic study

Transmission electron microscopy was used to examine internalized gap junctions (IGJ) in rabbit and rat ciliary epithelial cells. A prominent feature of all the specimens studied was the presence of different images of IGJ membrane that entrapped a portion of an adjoining cell. We documented and analyzed more than 500 gap junction (GJ) vacuoles and invaginations, the latter comprising less than 20% of all the structures examined. With ten exceptions found in non-pigmented cells, all the IGJ were unidirectionally internalized within the cytoplasm of pigmented epithelial cells. Morphological signs of autophagic degradation of GJ vacuoles were observed. An essential finding was that once a GJ membrane started to invaginate, a "lucidation" of a part of the protruding cytoplasm occurred; no planar GJ membranes exhibited such an alteration. The present finding suggest that IGJ derived from the epithelium of ciliary processes arise through an invagination-endocytosis mechanism and are degraded autophagically. This phenomenon may be relevant to aqueous humor production.