Reduced climbing and increased slipping adaptation in cochlear hair cells of mice with Myo7a mutations.

Mutations in Myo7a cause hereditary deafness in mice and humans. We describe the effects of two mutations, Myo7a(6J) and Myo7a(4626SB), on mechano-electrical transduction in cochlear hair cells. Both mutations result in two major functional abnormalities that would interfere with sound transduction. The hair bundles need to be displaced beyond their physiological operating range for mechanotransducer channels to open. Transducer currents also adapt more strongly than normal to excitatory stimuli. We conclude that myosin VIIA participates in anchoring and holding membrane-bound elements to the actin core of the stereocilium. Myosin VIIA is therefore required for the normal gating of transducer channels.

Gut morphology and morphometry in the epauletted Wahlberg's fruit bat (Epomophorus wahlbergi, Sundevall, 1846).

The morphological adaptations of the fruit bat small intestine to which the high functional efficiency could be related and the possible landmarks delineating the various parts of the gut were examined. The stomach was the carnivorous type with large rugae spanning the entire luminal aspect down to the pyloric sphincter, which was reflected internally as a prominent fold. Externally, the intestine was a continuous tube uninterrupted by any structures. The cranial fifth of the small gut had long, branching and anastomosing villi, which caudally turned to finger-like discrete structures that became rather short and stumpy and diminished at the beginning of the colon. The colon had longitudinal folds that were macroscopically discernible from the mucosal aspect of the opened intestine and that continued into the rectum. The small gut formed 94% of the whole intestinal length, the colon and the rectum taking 4 and 2%, respectively. Ultrastructurally, the enterocyte showed a prominent brush border and the lateral membranes were modified into numerous tortuous interdigitating processes. Adjacent enterocytes were joined by these processes through desmosomes. The processes also participated in pinocytotic fluid uptake from the intercellular spaces with resultant numerous intracellular vacuoles of varied sizes. Solutes absorbed into the cells were probably first passed into the intercellular compartment to create a concentration gradient thus enhancing further absorption into the cell. We conclude that the uniquely elaborate ultrastructure of the enteric epithelium coupled with the vast microvillous surface areas reported elsewhere are partly responsible for the very high absorption rates reported in the fruit bat small intestine.

Stereological studies on red corpuscle size produce values different from those obtained using haematocrit- and model-based methods.

The routine methods for estimating erythrocyte size (volume and surface area) are not generally unbiased. Using geometric models introduces a bias determined by the ways in which real red blood corpuscles depart in size and shape from the simplistic ideal. Employing haematocrit and red corpuscle count to estimate mean corpuscular volume relies on an implicit assumption that erythrocytes fill three-dimensional space. However, a biconcave circular disc cannot be space-filling. The bias is positive and its magnitude depends on erythrocyte geometry and packing density within the centrifuge pellet. We have estimated the volumes, surface areas and shape factors of red blood corpuscles in normal adults (three males, three females) using transmission electron microscopy and stereology. We confirm the lack of sexual dimorphism and find that the mean corpuscular volume is 44 fl (between-subject coefficient of variation 5%), mean membrane surface area is 87 microns2 (6%) and the shape factor is 18.4 fl/fl (11%). The surface is 44% greater than that of a sphere of equal volume. The possible reasons for discrepancies with standard haematological values are discussed. On the basis of observed volumes, we predict that red blood corpuscles account for only 51% of the volume of the red column in standard haematocrit pellets.

Epithelial restitution in the large intestine of the rat following insult with bile salts.

In situ loops of large bowel of anaesthetised rats were used to observe epithelial restitution following surface desquamation using solutions of bile salts. The treatment induced complete surface desquamation but no disruption of the basal lamina. There was evidence of, cell migration at 30 min, and a complete surface epithelium two h post treatment. Neither a continuous contact between migrating cells and the basal lamina, nor a complete covering of secreted mucus, appeared necessary for epithelial restitution to occur.