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J K Reynhout

Publications and source records attributed to J K Reynhout.

11 recordsLinked to original sources
PubMed2001

Ser364 of connexin43 and the upregulation of gap junction assembly by cAMP.

The assembly of gap junctions (GJs) is a process coordinated by growth factors, kinases, and other signaling molecules. GJ assembly can be enhanced via the elevation of cAMP and subsequent stimulation of connexon trafficking to the plasma membrane. To study the positive regulation of GJ assembly, fibroblasts derived from connexin (Cx)43 knockout (KO) and wild-type (WT) mice were transfected with WT Cx43 (WTCx43) or mutant Cx43. GJ assembly between untransfected WT fibroblasts or stably transfected WTCx43/KO fibroblasts was increased two- to fivefold by 8Br-cAMP, and this increase could be blocked by inhibition of cAMP-dependent protein kinase (PKA) or truncation of the Cx43 COOH terminus (CT). Although serine 364 (S364) of the Cx43 CT was determined to be a major site of phosphorylation, the molar ratio of Cx43 phosphorylation was not increased by 8Br-cAMP. Importantly, GJ assembly between either S364ECx43/KO or S364ECx43/WT fibroblasts was stimulated by 8Br-cAMP, but that between S364ACx43/KO or S364PCx43/KO fibroblasts was not stimulated, indicating that phosphorylation or a negative charge at S364 is required for enhancement of GJ assembly by cAMP. Furthermore, GJ assembly between S364ACx43/WT fibroblasts could be stimulated by 8Br-cAMP, but could not be between S364PCx43/WT fibroblasts. Thus, S364PCx43 interferes with enhanced GJ assembly when coexpressed with WTCx43.

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PubMed1994

Membrane permeability changes during Rana oocyte maturation.

A transition from an open system to a closed one must occur during the complex process of meiotic maturation of the amphibian oocyte. Membrane permeability to urea in Rana oocytes following progesterone stimulation was determined, and the largest decrease was found to coincide with germinal vesicle breakdown. These findings suggest that the timing of the disappearance of membrane permeability correlates with developmental events that prepare the oocyte for a hostile environment.

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PubMed1994

Urea transport in frog oocytes: effect of osmotic stress and vasopressin.

The transport of water and urea across biological membranes are considered to traverse separate channels or pores. While vasopressin responsiveness correlates with increased urea/water permeability in some epithelia, oocytes provide a single cell system to determine the coupling relationship. Urea transport under isotonic and hypotonic conditions are determined in full-grown frog oocytes in follicles. We found that urea reached equilibrium distribution (ratio of 14C-urea concentrations inside and outside of the oocyte) rapidly and remained equilibrated over 20 h period, independent of external urea concentrations. Thus, urea uptake is not via an active transport system. While hypotonicity caused oocytes to swell, vasopressin did not exert additional effect. Under hypotonic conditions, distribution ratios of water and urea changed in different ways supporting the view that distinguishable channels (pathways) were involved. It appeared that no correlated changes due to vasopressin occurred under osmotic challenge. The response pattern to vasopressin was different between renal epithelia and frog oocyte.

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PubMed1992

An activator of protein kinase C inhibits gap junction communication between cultured bovine lens cells.

Currently little is known about the regulation of gap junction communication in the lens. We report here on the effects of the protein kinase C activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), on cultured bovine lens cells which appeared to be epithelial in nature. Dramatically reduced intercellular transfer of the fluorescent dye Lucifer yellow was observed when the cultured lens cells were treated with octanol, a known inhibitor of gap junction communication. TPA (4 beta isomer) was also shown to reduce intercellular permeability within these cultures. In contrast, an inactive form of TPA, 4 alpha-TPA, did not decrease dye transfer. Permeability was evaluated in terms of both the number of cells receiving dye and the rate of decrease in fluorescence intensity in the injected cell. The maximum decreases in dye transfer occurred at 2 h of TPA treatment and dye transfer gradually increased to control levels over a time course of many hours. Incubation of cultures with 32Pi and immunoprecipitation using antibodies to the N- and C-terminal regions of connexin43 demonstrated a gap junction phosphoprotein of 43,000 Da. Phosphorylation of connexin43 increased during the first 2 h of TPA treatment. These results suggest that protein kinase C has a direct or indirect effect on gap junction communication in cultured lens cells.

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PubMed1984

Regional water changes during oocyte meiotic maturation: evidence of ooplasmic segregation.

Cryomicrodissection was used to measure the intraoocytic distribution of water before and during meiotic maturation in Rana pipiens oocytes. Animal ooplasm contained about 10% more water in matured than in ovarian oocytes. The increase was not dependent on the uptake of extracellular water, occurring even when oocytes were matured in a paraffin oil medium. Rather, animal ooplasm hydration appeared to be due to an increase in the volume fraction occupied by cytoplasm (reduced yolk density) through: (1) migration of cytoplasm from the vegetal to animal hemisphere and (2) mixing of ooplasm with nuclear sap during germinal vesicle breakdown (GVBD). Cytoplasmic migration (or ooplasmic segregation) began prior to GVBD, probably within an hour of exposure to progesterone and appeared to continue through the period of GVBD. The volume of cytoplasm that moved significantly reduced water concentrations in vegetal ooplasm at 6 hr postprogesterone and offset any subsequent water gain due to the mixing of nuclear sap and vegetal ooplasm at GVBD. The findings suggest that segregational movements are among the early maturational changes entrained by progesterone. Ooplasmic segregation is considered in the context of theories of cytomatrix movement in which control resides in regional Ca2+ activity gradients. We address the problem of the vegetal----animal directionality of movement and suggest that the annulate lamellae play a role.

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PubMed1979

Reference phase analysis of free and bound intracellular solutes. I. Sodium and potassium in amphibian oocytes.

A method is described for the quantitative determination of free and bound solute concentrations in the cytoplasm of intact cells. The method includes (a) introduction of a gelatin gel reference phase (RP) into the cytoplasm; (b) diffusion of dissolved substances between cytoplasm and RP, (c) cell quenching to - 196 degrees C to prevent subsequent solute redistributions, (d) ultra-low temperature microdissection to isolate RP and cytoplasm samples, and (e) analysis of isolates for solute and water content. In normal oocytes of the salamander, Desmognathus ochrophaeus, free or RP Na+ and K+ are 21.0 +/- 1.1 and 128.8 +/- 2.4 mu eq/ml, respectively, and vary stoichiometrically in altered oocytes. Overall cytoplasmic concentrations are 75.2 +/- 2.7 mu eq Na+/ml and 88.6 +/- 1.5 mu eq K+/ml. Cytoplasmic chemical activities are 16.2 mu eq Na+/ml and 99.2 mu eq K+/ml, corresponding to activity coefficients of 0.22 and 1.12, respectively. The results demonstrate unambiguously that (a) oocytes actively transport Na+ and K+, and (b) cytoplasm has important binding properties which differentiate it from an ordinary aqueous solution. These cytoplasmic properties are investigated in the following paper.

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PubMedDate not supplied

Identification of interstitial cells of Cajal in the digestive tract of turkeys (Meleagris gallopavo).

Interstitial cells of Cajal (ICCs) were identified in the digestive tract of turkeys by electron microscopy. ICCs have been implicated as sources of pacemaking slow wave potentials that initiate peristalsis in the stomach and intestines in mammals. The gastroduodenal contraction cycle in turkeys, however, is uniquely coordinated by a neurogenic pacemaker in the isthmus area between the glandular stomach and the gizzard, and this controls the coordinated phasic contractions of the muscles of the gizzard, duodenum and glandular stomach. Thus, it becomes important to look for the presence and distribution of ICCs in the avian digestive tract, especially in the gizzard and duodenum. This investigation has identified that cells are present which contain the typical characteristics of ICCs including: numerous mitochondria, caveolae, thin processes, basement membrane, filaments, rough ER, Golgi, and occasional gap junctions. They were mostly located in the region of the myenteric plexus between the longitudinal and circular muscle layers and occasionally within the longitudinal muscle layer. They were frequently near nerve axon bundles and were usually surrounded by collagen, elastin fibers, and occasional fibroblasts or blood vessels. ICCs were easily found in the ileum, but were also present in the duodenum, cecum, and rectum. None were found in the serosal region of the thick muscle of the gizzard. The presence of ICCs in the turkey duodenum, which like the gizzard is under neurogenic control, suggests that ICCs may play a role(s) in addition to initiating peristalsis.

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