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Sodium balance, and ultimately blood pressure and extracellular fluid volume, is maintained by precise regulation of the activity of the epithelial sodium channel (ENaC). In a Xenopus kidney epithelial cell line (A6), exposure of the apical membrane to the protease inhibitor aprotinin reduces transepithelial sodium transport. Sodium-channel activity can be restored by subsequent exposure to the nonspecific protease trypsin. Using A6 cells and a functional complementation assay to detect increases in ENaC activity, we have cloned a 329-residue protein belonging to the serine protease family. We show that coexpression of this protein with ENaC in Xenopus oocytes increases the activity of the sodium channel by two- to threefold. This channel-activating protease (CAP1) is expressed in kidney, gut, lung, skin and ovary. Sequence analysis predicts that CAP1 is a secreted and/or glycosylphosphatidylinositol-anchored protein: ENaC activity would thus be regulated by the activity of a protease expressed at the surface of the same cell. This previously undiscovered mechanism for autocrine regulation may apply to other ion channels, in particular to members of the ENaC family that are present in neurons and epithelial cells.

The amiloride-sensitive epithelial sodium channel constitutes the rate-limiting step for sodium reabsorption in epithelial cells that line the distal part of the renal tubule, the distal colon, the duct of several exocrine glands, and the lung. The activity of this channel is upregulated by vasopressin and aldosterone, hormones involved in the maintenance of sodium balance, blood volume and blood pressure. We have identified the primary structure of the alpha-subunit of the rat epithelial sodium channel by expression cloning in Xenopus laevis oocytes. An identical subunit has recently been reported. Here we identify two other subunits (beta and gamma) by functional complementation of the alpha-subunit of the rat epithelial Na+ channel. The ion-selective permeability, the gating properties and the pharmacological profile of the channel formed by coexpressing the three subunits in oocytes are similar to that of the native channel.

The epithelial amiloride-sensitive sodium channel constitutes the rate limiting step for sodium reabsorbtion by the epithelial lining the distal part of the kidney tubule, the urinary bladder and the distal colon. Reabsorbtion of sodium through this channel, which is regulated by hormones such as aldosterone and vasopressin, is one of the essential mechanisms involved in the regulation of sodium balance, blood volume and blood pressure. Here we isolate a DNA from epithelial cells of rat distal colon and identify it by functional expression of an amiloride-sensitive sodium current in Xenopus oocyte. The deduced polypeptide (698 amino acids) has at least two putative transmembrane segments. Expression of this protein in Xenopus oocytes reconstitutes the functional properties of the highly selective amiloride-sensitive, epithelial sodium channel. The gene encoding this rat sodium channel subunit shares significant sequence similarity with mec-4 and deg-1, members of a family of Caenorhabditis elegans genes involved in sensory touch transduction and, when mutated, neuronal degeneration. We propose that the gene products of these three genes are members of a gene family coding for cation channels.

Measurements of the growth of aortic explants taken from rats after breeding show that arterial samples from rats with arteriosclerosis grow less than do samples taken from healthy rats. The retardation of growth due to arteriosclerosis is especially marked in samples taken from the abdominal aorta.

Increased Aortic Beta-Glucuronidase Activity with Progressively Severe Arteriosclerosis in Female Breeder Rats

MAN, in meeting his basic needs and cultural demands, often finds himself in conflict with other organisms. Throughout the world there are species of birds which create diverse problems ranging from crop damage to aircraft damage, with a consequent hazard to human life. Reports in the literature suggest several possible bird control procedures making use of digestible baits1–4. Wentworth et al.5, working with laboratory quail, suggest that spraying of eggs with mestranol may be an effective way to chemosterilize some birds.

A METHOD has been developed for measuring small rapid volume changes occurring in a muscle during a single twitch. In order to achieve the necessary sensitivity and speed of response, a capacitance transducer has been developed which uses a commercially available detector-amplifier circuit (the ‘Dynagage’, from Photocon Products). The changes are displayed on a cathode-ray oscilloscope. Single gastrocnemius and sartorius muscles from Rana pipiens are used.

AMONG the radioisotopes which are assimilated differentially in light and dark by phytoplankton or macrophytes are phosphorus-321, zinc-652, strontium-89 and 903, molybdenum-994 and caesium-1375. This communication considers this effect for strontium-85 in relation to primary productivity.

WE have obtained reliably reproducible measurements of the electric potentials developed in the eyes of euphausiid crustaceans during stimulation by light. Such measurements may provide an objective method for the laboratory study of vision and photoregulated behaviour in planktonic forms which undergo vertical migrations too extensive to be duplicated experimentally with any available equipment. Preliminary observations of two species from the San Diego Trough off California, and one from Loch Fyne in Scotland, are presented here.