The extracellular ß-1,3-endoglucanase EngA is involved in autolysis of Aspergillus nidulans.

AIMS: To elucidate the roles of the ß-1,3-endoglucanase EngA in autolysis of the filamentous fungus Aspergillus nidulans and to identify the common regulatory elements of autolytic hydrolases. METHODS AND RESULTS: A ß-1,3-endoglucanase was purified from carbon-starving cultures of A. nidulans. This enzyme is found to be encoded by the engA gene (locus ID: AN0472.3). Functional and gene-expression studies demonstrated that EngA is involved in the autolytic cell wall degradation resulting from carbon starvation of the fungus. Moreover, regulation of engA is found to be dependent on the FluG/BrlA asexual sporulation signalling pathway in submerged culture. The deletion of either engA or chiB (encoding an endochitinase) caused highly reduced production of hydrolases in general. CONCLUSIONS: The ß-1,3-endoglucanase EngA plays a pivotal role in fungal autolysis, and activities of both EngA and ChiB are necessary to orchestrate the expression of autolytic hydrolases. The production of cell wall-degrading enzymes was coordinately controlled in a highly sophisticated and complex manner. SIGNIFICANCE AND IMPACT OF THE STUDY: No information was available on the autolytic glucanase(s) of the euascomycete A. nidulans. This study demonstrates that EngA is a key element in fungal autolysis, and normal activities of both EngA and ChiB are crucial for balanced production of hydrolases.

Asexual sporulation signalling regulates autolysis of Aspergillus nidulans via modulating the chitinase ChiB production.

AIMS: Elucidation of the regulation of ChiB production in Aspergillus nidulans. METHODS AND RESULTS: Mutational inactivation of the A. nidulans chiB gene resulted in a nonautolytic phenotype. To better understand the mechanisms controlling both developmental progression and fungal autolysis, we examined a range of autolysis-associated parameters in A. nidulans developmental and/or autolytic mutants. Investigation of disorganization of mycelial pellets, loss of biomass, extra-/intracellular chitinase activities, ChiB production and chiB mRNA levels in various cultures revealed that, in submerged cultures, initialization of autolysis and stationary phase-induced ChiB production are intimately coupled, and that both processes are controlled by the FluG-BrlA asexual sporulation regulatory pathway. ChiB production does not affect the progression of apoptotic cell death in the aging A. nidulans cultures. CONCLUSIONS: The endochitinase ChiB plays an important role in autolysis of A. nidulans, and its production is initiated by FluG-BrlA signalling. Despite the fact that apoptosis is an inseparable part of fungal autolysis, its regulation is independent to FluG-initiated sporulation signalling. SIGNIFICANCE AND IMPACT OF THE STUDY: Deletion of chiB and fluG homologues in industrial filamentous fungal strains may stabilize the hyphal structures in the autolytic phase of growth and limit the release of autolytic hydrolases into the culture medium.

Hypokalemia in rats produces resistance to dysrhythmias under halothane anesthesia.

The arrhythmogenic threshold was investigated during acute and chronic hypokalemia under halothane anesthesia with an epinephrine challenge in the rat model. It was hypothesized that in the setting of severe hypokalemia, general anesthesia would be arrhythmogenic and would be exaggerated with increased levels of catecholamines. Rats were divided into four groups as follows: normokalemic control (group I, n = 10), acute hypokalemia with furosemide (group II, n = 16), acute hypokalemia with hyperventilation (group III, n = 18), and chronic hypokalemia induced by a low potassium (K+) diet (group IV, n = 22). There were no significant differences (P less than .05) in baseline K+ and arterial blood gases among the four groups. There was a significant difference between groups I and II and groups I and IV (P less than 0.05) in serum K+ values after the low K+ diet, but no differences were observed between groups II and IV or groups I and III in serum K+ levels. There was no significant difference in myocardial tissue K+ among the four groups. There was a significant difference in the arrhythmic dose of epinephrine among the four groups (P less than 0.05). Acute hypokalemia was more prone to dysrhythmias than chronic hypokalemia. However, compared with control, acute and chronic hypokalemia groups were resistant to dysrhythmias is probably based on compensatory mechanisms. The heart seems more resistant to K+ changes than skeletal muscle. This resistance is associated with compensation by the cardiac muscle sodium pump in the face of K+ depletion. Hypokalemia per se did not increase the incidence of dysrhythmias under halothane anesthesia in rats.

Shivering following retrobulbar block.

A case of a severe but brief period of shivering following a retrobulbar block (RBB) is presented. The shivering occurred within two minutes after completion of the RBB and subsided gradually within five minutes, without specific treatment. The patient remained conscious during the episode of shivering. The shivering was so abrupt and severe as to be misjudged as a seizure, but its onset appeared to be slower than a seizure. The mechanism of shivering appeared to be the central spread of local anaesthetic solution into the brain stem, along the optic nerve. Shivering may be a warning sign of brain stem anaesthesia and demands special care to anticipate life-threatening complications.