2006 GEP-ISFG collaborative exercise on mtDNA: reflections about interpretation, artefacts, and DNA mixtures

We report the results of the seventh edition of the GEP-ISFG mitochondrial DNA (mtDNA) collaborative exercise. The samples submitted to the participant laboratories were blood stains from a maternity case and simulated forensic samples, including a case of mixture. The success rate for the blood stains was moderate ( approximately 77%); even though four inexperienced laboratories concentrated about one-third of the total errors. A similar success was obtained for the analysis of mixed samples (78.8% for a hair-saliva mixture and 69.2% for a saliva-saliva mixture). Two laboratories also dissected the haplotypes contributing to the saliva-saliva mixture. Most of the errors were due to reading problems and misinterpretation of electropherograms, demonstrating once more that the lack of a solid devised experimental approach is the main cause of error in mtDNA testing.

Secretory responses of intact glomus cells in thin slices of rat carotid body to hypoxia and tetraethylammonium

We have developed a thin-slice preparation of whole rat carotid body that allows us to perform patch-clamp recording of membrane ionic currents and to monitor catecholamine secretion by amperometry in single glomus cells under direct visual control. In normoxic conditions (P(O(2)) approximately 140 mmHg; 1 mmHg = 133 Pa), most glomus cells did not have measurable secretory activity, but exposure to hypoxia (P(O(2)) approximately 20 mmHg) elicited the appearance of a large number of spike-like exocytotic events. This neurosecretory response to hypoxia was fully reversible and required extracellular Ca(2+) influx. The average charge of single quantal events was 46 +/- 25 fC (n = 218), which yields an estimate of approximately 140,000 catecholamine molecules per vesicle. Addition of tetraethylammonium (TEA; 2-5 mM) to the extracellular solution induced in most (>95%) cells tested (n = 32) a secretory response similar to that elicited by low P(O(2)). Cells nonresponsive to hypoxia but activated by exposure to high external K(+) were also stimulated by TEA. A secretory response similar to the responses to hypoxia and TEA was also observed after treatment of the cells with iberiotoxin to block selectively Ca(2+)- and voltage-activated maxi-K(+) channels. Our data further show that membrane ion channels are critically involved in sensory transduction in the carotid body. We also show that in intact glomus cells inhibition of voltage-dependent K(+) channels can contribute to initiation of the secretory response to low P(O(2)).

Neurotrophic influences on corneal epithelial cells

Innervation plays an important role in the maintenance of corneal structure and function. Neuropeptides contained in corneal nerves may be involved in these effects. This study was aimed to determine the influence of trigeminal and sympathetic neurons and of neuropeptides on proliferative activity of corneal epithelial cells in vitro. Corneal epithelial cells from adult rabbits were cultured alone or cocultured either with sensory neurons from the trigeminal ganglion or sympathetic cells from the superior cervical ganglion of newborn rabbits. Neurons and corneal epithelial cells shared the culture medium but lacked physical contact. After 2 or 7 days of coculture, or after treatment with substance P (SP) and/or calcitonin gene-related peptide (CGRP), the number of corneal cells was determined with a haemocytometer, and the incorporation of 3H-thymidine into corneal epithelial cells analysed by scintillation counting. Cell number and 3H-thymidine incorporation increased 3 and 2.5 times respectively (P < 0.01; P < 0.05), after 2 days of coculture of corneal epithelial cells with trigeminal neurons but this increase was reversed after 7 days of coculture. Sympathetic neurons had a stimulating effect on corneal epithelial cell proliferation that was apparent after 7 days of coculture (P < 0.01). A single administration of SP (10 microM) produced an increase in 3H-thymidine incorporation after 1 hr and an enhanced number of corneal epithelial cells 24 hr later. The same effect could be obtained by repeated administration of lower concentrations of SP (0.1 microM, six times over a 24 hr period). CGRP (1 microM) inhibited mitotic activity of corneal cells 12 hr after treatment. The effect could be reversed by simultaneous administration of SP (0.1 microM). These results indicate that trigeminal and sympathetic neurons modulate proliferation and perhaps differentiation of corneal epithelium cells in vitro. A stimulating effect was also obtained with SP while mitotic activity was inhibited by CGRP, thus suggesting that peptides contained in sensory nerve terminals may contribute to neural influences on epithelial cell proliferation.