Una Smith

Exocytosis in the Adrenal Medulla Demonstrated by Freeze-Etching

Replicas of fractured chromaffin cells are indicative of a range of activities thought to characterize exocytosis, including attachment of secretory vesicles to the plasma membrane, fusion, extrusion of contents, and membrane retrieval. Exocytosis sites are abundant on stimulated cells but are infrequent when calcium is omitted from the system.

Freeze-fractured lamellar body membranes of the rat lung great alveolar cell.

Abstract Lamellar body inclusions of the rat lung great alveolar cell (=Type II alveolar cell) have been studied by conventional thin sectioning and freeze-etching. The former confirmed previous reports that lamellar bodies are released into the alveolar space, and release inter alia tubular myelin, associated with lung surfactant. Replicas of fixed or unfixed freeze-etched material reveal the intracellular lamellar bodies as highly structured, in which lamellae may be concentric or disposed in parallel planar series. Fractured lamellae bear ca. 100 A particles, and linear sculpturing similar in spacing to extracellular tubular myelin. Transverse fractures show that lamellae are ca. 60 A in width, comprising two ca. 20 A components. The appearance of freeze-fractured and etched lipoprotein and phospholipid membranes is discussed, and it is proposed that the surfaces revealed within the lamellar body are associated with the elaboration of surfactant components.

A rapid, simple method for isolating pinocytotic vesicles and plasma membrane of lung

Abstract We have found means of isolating pinocytotic vesicles and attached plasma membrane from the low speed (200 × g ) supernatant of homogenates of lung. In lung, 5′-nucleotidase is restricted to pinocytotic vesicles and areas of incipient vesicle formation along the plasma membrane. In our method, P i released from AMP is precipitated as lead phosphate at the subcellular site of 5′-nucleotidase. The resulting increase in density allows collection of pinocytotic vesicles and attached plasma membrane as a pellet after centrifugation through sucrose ( d = 1.18) at 250 × g . The final pellet contains long strands of plasma membrane, and the vesicles retain their characteristic morphology including the delicate diaphragm covering their stomata. The entire procedure can be performed in less than 90 min.

Fine structure of Methanomonas methanooxidans

SummaryThin sections of the obligate methane oxidizing bacterium, Methanomonas methanooxidans, reveal extensive intracytoplasmic membranes. These always occur in a peripheral arrangement. They appear similar to those in other bacteria which utilize specific energy sources. Their structure and function is discussed.

Aspects of fine structure and function of the subcommissural organ of the embryonic chick

The fine structure of the subcommissural organ (SCO) of the embryonic chick has been studied. No evidence of secretory release was obtained. The SCO seems not to be involved in such previously suggested roles as water regulation or response to varying light cycles. The introduction of electron dense markers into the 3rd ventricle demonstrated rapid and massive uptake into coated pits and coated vesicles of the ependymal cells and its subsequent incorporation into terminal bodies. It is suggested that the uptake of macromolecules from the cerebrospinal fluid may be an important and hitherto unsuspected function of the SCO.

An Electron Microscopic Study of the Vascular Endothelium as a Site for Bradykinin and Adenosine-5′-Triphosphate Inactivation in Rat Lung

Bradykinin is inactivated in one circulation through the intact or “blood-free rat lung (1). Inactivation of bradykinin occurs by hydrolysis of peptide bonds, yet the effluent of a blood-free lung preparation does not contain sufficient hydrolase activity to account for this extremely rapid and efficient degradation. Furthermore, there is no measurable retention of bradykinin or its peptide fragments by the lung. It seems likely, therefore, that bradykinin is inactivated by cellular enzymes at or near the endothelium of pulmonary blood vessels.