Unraveling the relationship between macula densa cell volume and luminal solute concentration/osmolality.

At the macula densa, flow-dependent changes in luminal composition lead to tubuloglomerular feedback and renin release. Apical entry of sodium chloride in both macula densa and cortical thick ascending limb (cTAL) cells occurs via furosemide-sensitive sodium-chloride-potassium cotransport. In macula densa, apical entry of sodium chloride leads to changes in cell volume, although there are conflicting data regarding the directional change in macula densa cell volume with increases in luminal sodium chloride concentration. To further assess volume changes in macula densa cells, cTAL-glomerular preparations were isolated and perfused from rabbits, and macula densa cells were loaded with fluorescent dyes calcein and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate. Cell volume was determined with wide-field and multiphoton fluorescence microscopy. Increases in luminal sodium chloride concentration from 0 to 80 mmol/l at constant osmolality led to cell swelling in macula densa and cTAL cells, an effect that was blocked by luminal application of furosemide. However, increases in luminal sodium chloride concentration from 0 to 80 mmol/l with concomitant increases in osmolality caused sustained decreases in macula densa cell volume but transient increases in cTAL cell volume. Increases in luminal osmolality with urea also resulted in macula densa cell shrinkage. These studies suggest that, under physiologically relevant conditions of concurrent increases in luminal sodium chloride concentration and osmolality, there is macula densa cell shrinkage, which may play a role in the macula densa cell signaling process.

Current mechanisms of macula densa cell signalling.

Macula densa cells couple renal haemodynamics, glomerular filtration and renin release with tubular fluid salt and water reabsorption. These cells detect changes in tubular fluid composition through a complex of intracellular signalling events that are mediated by membrane transport pathways. Increases in luminal fluid sodium chloride concentration result in alterations in cell sodium chloride concentration, cytosolic calcium, cell pH, basolateral membrane depolarization and cell volume. Macula densa signalling then involves the production and release of specific paracrine signalling molecules at their basolateral membrane. Upon moderate increases in luminal sodium chloride concentration macula densa cells release increasing amounts of ATP and decreasing amounts of prostaglandin E(2), thereby increasing afferent arteriolar tone and decreasing the release of renin from granular cells. On the other hand, further increases in luminal concentration stimulate the release of nitric oxide, which serve to prevent excessive tubuloglomerular feedback vasoconstriction. Paracrine signalling by the macula densa cells therefore controls juxtaglomerular function, renal vascular resistance and participates in the regulation of renin release.

Amanita poisoning during the second trimester of pregnancy. A case report and a review of the literature.

Amanita phalloides-type mushroom poisoning is well recognized as causing acute liver injury and often death. Less is known, however, of whether maternal Amanita poisoning is associated with fetal damage or not. In August 1991 four members of a family were hospitalized with food intoxication caused by Amanita phalloides and Amanita verna. One of them died from hepatic and renal failure. The survivors included a 26-year-old woman in the 23rd week of pregnancy. Her clinical symptoms and blood chemistry data (lowest prothrombin activity 23%) indicated intoxication of medium severity. The management consisted of i.v. hydration, forced diuresis, and administration of silibinin, high-dose penicillin, thioctic acid, hydrocortisone, vitamin K, and fresh frozen plasma. Sonographic and obstetric controls failed to show any fetal abnormalities in the acute phase of poisoning. In the 38th week of pregnancy she gave birth to a healthy baby, who has subsequently undergone an undisturbed development. This observation indicated that severe fetal damage did not occur in maternal Amanita poisoning in the second trimester of pregnancy. Thus, at least from the second trimester on, maternal Amanita poisoning is not necessarily an indication for induced abortion.