Morphological changes of the adipose cell plasma membrane during lipolysis.

Abstract

Morphological changes of the plasma membrane in the white adipose cell associated with lipid mobilization were assessed qualitatively and quantitatively on freeze-fracture replicas of epididymal adipose tissue from fasted and from streptozotocin-diabetic rats. The number of plasma membrane invaginations and intramembranous particles were evaluated per square micrometer of membrane and per entire adipocyte. These two determinations show that the number per square micrometer (local concentration) of both structural features progressively increases with the duration of diabetes and fasting, while that at the same time their number per entire cell (total content) remains unchanged. These data thus show: (a) a reorganization of the adipose cell plasma membrane during lipolysis; and (b) that this reorganization can be detected only by determining the concentration and the total content of the structural features of the membrane involved.Previous studies of the changes induced by lipolysis in the morphology of the white adipose cell have shown an increase in the number of microvesicular invaginations (so-called "pinocytosis") of the plasma membrane during lipolysis (13,14,16,19,22,23). However, these data remained essentially qualitative since they were based on the examination of conventional thin sections which were not assessed by a morphometric approach. The application of the freeze-fracturing technique (11) to the adipose tissue has made it possible to study large areas of the cell membrane and quantitatively to assess structural features of the adipocyte plasma membrane such as membrane invaginations and intramembranous particles under various experimental conditions. For example, we have been able to demonstrate quantitative changes in the organization of the adipose cell plasma membrane induced by lipolytic and lipogenic hormones applied to the adipose tissue in vitro (3). In the present work, we have extended these studies by assessing quantitatively, in freezefracture replicas, the adipose cell membrane organization in the course of an acute lipolysis induced in vivo by fasting or streptozotocin diabetes. MATERIALS AND METHODS AnimalsYoung male Wistar rats (200-290 g) were used throughout.Fasting 20 animals were placed in individual cages containing water but no food while 6 others used as controls were fed normally with Purina Chow. Six rats of the fasting group were killed after 3 days, six after 6 days, and four after 9 days (four died at the 8th day of fasting). Diabetes18 rats were injected in the tail vein with streptozotocin (75 mg/kg) kindly supplied by Dr. W. Dulin (The 104

Morphology, histochemistry, and differentiation of the cat's epiglottic cartilage: A supporting organ composed of elastic cartilage, fibrous cartilage, myxoid tissue, and fat tissue

“…Moreover, electron microscopy proved that fat cells in the EC are true adipocytes, provided with surface vesicles and continuous basal laminae, as generally described for adipocytes (Carpentier et al, 1977;Cinti et al, 1984;Rhodin, 1974).…”

“…Physicochemical properties of the alcianophilic ground substance in myxoid and cartilage areas most likely remain constant over time. By contrast, the volume of adipocytes can change significantly according to metabolic situations (Carpentier et al, 1977). Therefore, we speculate that the rigidity of the supporting organ can be adapted by controlling the metabolic state of the fat lobules encountered.…”

Assessment of S100 protein expression in the epididymis of juvenile and adult European bison.

“…Still others, in the electron microscopic picture, observed a positive reaction for S100 protein in continuous type capillary endothelia in rat testis, while negative in fenestrated type endothelium [31]. Moreover, Carpentier [32] observed an increased amount of S100 protein positive vesicles in endothelial cells of adjacent capillaries during lipolysis. Since one of the major roles of endothelial cells is to transport bioactive substances from blood into the perivascular space, Iwanaga [28] suggested that S100 protein in the continuous type capillary endothelium may be involved in the transport of fatty acids and/or other substances.…”

Morphological studies on adipocytes from obese rats - scanning and freeze-fracturing electron microscopy.

“…This may be because of the technical difficulty of examining these cells by electron microscopy owing to their very high lipid content. Recently, Carpentier et al (8,9), and Jarett et al (26) examined the morphology of adipocytes of young rat s during lipolysis by the freeze-fracture method and scanning electron microscopy. Our previous papers desribed the morphology of isolated adipocytes examined by transmission and scanning electron microscopies (18,19).…”

“…For freeze-fracturing electron microscopy, small pieces of adipose tissue were fixed for 2 hr in 2.5% glutaraldehyde solution in phosphate buffer, pH 7.4, and then treated for at least 30 min with 20% glycerol in Krebs-Ringer phosphate buffer. They were then rapidly frozen in liquid nitrogen, fractured and shadowed in an FD-2A apparatus (Eiko Engineering Co.) as described by Carpentier et al (9). Adipocytes were difficult to freeze-fracture.…”