A tubulo-cisternal endoplasmic reticulum system in the potassium transporting marginal cells of the stria vascularis and effects of the ototoxic diuretic ethacrynic acid

Summary Sections of metal impregnated tissue and freeze-fracture have been used to examine intracellular membrane systems in marginal cells of the stria vascularis in mammalian cochleae. A continuous network of elements of the smooth endoplasmic reticulum was revealed. Notable features of this system were a series of flattened cisternae just inside and parallel with the lateral plasma membrane in continuity with an apical network of tubules, cisternae and sheets oriented in parallel with the luminal membrane. The whole system was closely associated with mitochondria. These characteristics suggest that the potassium transporting marginal cells possess a tubulo-cisternal endoplasmic reticulum (TER) like that found in many sodium transporting epithelial cells. The lateral elements of the TER dilated, appearing like vacuoles, and opened to the lateral extracellular space in response to the effects of ethacrynic acid. This diuretic impairs ion transport in the stria vascularis. It is suggested that the TER in marginal cells is involved in the transport of ions and fluid from the cell to the intercellular space when ion balance is disturbed and may play a role in cell volume regulation.This work was supported by the Medical Research CouncilPart of this work was presented at the 18th Workshop on Inner Ear Biology, Montpellier, September, 1981     

Potentiation of arginine-induced glucagon secretion by adenosine

Adenosine and the synthetic adenosine agonists 2-chloroadenosine and N⁶-(L-2-phenylisopropyl)-adenosine were tested for effects on hormone secretion from the rat isolated perfused pancreas. These nucleosides, at concentrations of 5 μM, markedly potentiated both phases of arginine-induced glucagon release; the two synthetic agonists were more effective than adenosine. In the absence of arginine, each of the nucleosides induced a transient burst of glucagon. In contrast, adenosine and both synthetic agonists inhibited arginine-induced insulin secretion to varying degrees and caused only negligible insulin release when perfused without arginine. The adenosine antagonist 8-($\text{p}$-sulfophenyl)-theophylline prevented the actions of adenosine on hormone release from the pancreas. Our data suggest that adenosine potentiation of arginine-induced glucagon release may be mediated via adenosine receptors on alpha cell membranes; such a mechanism could provide an important endogenous control over glucagon secretion.     

Comparative properties of ferredoxins from a marine and freshwater species of Porphyridium

Ferredoxins were isolated from the freshwater red alga Porphyridium aerugineut, and from Porphyridium cruentum, a related marine species. A sin     

Arterial imaging with computerized fluoroscopy

Computerized fluoroscopy (CF) allows visualization of any segment of the arterial vascular system with intravenous injection of small volumes of standard iodinated contrast media. Because it avoids the risk of arterial puncture and the need for hospitalization, this technique is safer and more economical than standard arteriography. Because of these advantages, CF is likely to expand the role of arteriography in the clinical management of vascular disease. Computerized arteriographic imaging requires an intravenous power injection of 40 to 60 cc of iodinated contrast media. Immediately after injection, six to ten fluoroscopic images (1/15 sec duration) are obtained at 1.5-sec intervals. The first image serves as a mask from which subsequent images are serially subtracted by means of a digital video image processor. The sequence of different images is contrast enhanced and stored on a video disk. Video images are converted to hard copy arteriography with a standard multiformat camera. Technical failures (<5%) may result from patient motion, inadequate peripheral venous access, or extravasation of contrast media. Nearly 600 computerized intravenous arteriograms have been performed in 240 patients with peripheral vascular disease. Qualitative com-parisons with standard arteriograms suggest a close correlation between these two imaging techniques. Computerized fluoroscopy allows the identification of atheromatous plaque ulceration, stenoses, occlusions, and aneurysms. This method has been used to visualize the aortic arch and its branches, the cervical and intracranial vessels, the abdominal aorta, and arteries of the extremities. Computerized fluoroscopy has great potential as a method for safe, simple diagnostic screening and assessment of the postoperative patient.     

Fast atom bombardment: A new mass spectrometric method for peptide sequence analysis

We have studied a selection of peptides using a new mass spectrometric ionisation technique - fast atom bombardment (FAB). We define the fragmentation pathways observed and comment on the utility in sequence analysis. A simple acetylation experiment is shown to aid rapid sequence assignment.     

Vascular smooth muscle mitochondria: Magnesium content and transport

Endogenous magnesium content and magnesium transport of isolated bovine vascular smooth muscle mitochondria were studied. Mitochondria isolated from atherosclerotic bovine arteries contained two to three times as much magnesium (178 nmol/mg of mitochondrial protein) as those isolated from normal arteries (67 nmol/mg of mitochondrial protein). Electron-opaque granules were visible in the unstained unfixed mitochondria and could be shown with electron probe analysis to consist of magnesium, calcium, and phosphorus. At concentrations of external Mg²⁺ from 0 to 6 mm, the vascular smooth muscle mitochondria exhibited respiratory substrate-supported release of Mg²⁺ as studied with metallochromic indicator, eriochrome blue, using dual-wavelength spectrophotometry. The maximal velocity of energized release (3 nmol of Mg²⁺/s/mg of mitochondrial protein) was observed at 4 mm external Mg²⁺ and the half-maximal transport occurred at 0.5 mm.