Rearrangements of the cytoskeleton and cell contacts induce process formation during differentiation of conditionally immortalized mouse podocyte cell lines.

Mature podocytes are among the most complex differentiated cells and possess a highly branched array of foot processes that are essential to glomerular filtration in the kidney. Such differentiated podocytes are unable to replicate and culturing of primary podocytes results in rapid growth arrest. Therefore, conditionally immortalized mouse podocyte clones (MPC) were established, which are highly proliferative when cultured under permissive conditions. Nonpermissive conditions render the majority of MPC cells growth arrested within 6 days and induce many characteristics of differentiated podocytes. Both proliferating and differentiating MPC cells express the WT-1 protein and an ordered array of actin fibers and microtubules extends into the forming cellular processes during differentiation, reminiscent of podocyte processes in vivo. These cytoskeletal rearrangements and process formation are accompanied by the onset of synaptopodin synthesis, an actin-associated protein marking specifically differentiated podocytes. In addition, focal contacts are rearranged into an ordered pattern in differentiating MPC cells. Most importantly, electrophysiological studies demonstrate that differentiated MPC cells respond to the vasoactive peptide bradykinin by changes in intracellular calcium concentration. These results suggest a regulatory role of podocytes in glomerular filtration. Taken together, these studies establish that conditionally immortalized MPC cells retain a differentiation potential similar to podocytes in vivo. Therefore, the determinative steps of podocyte differentiation and process formation are studied for the first time using an inducible in vitro model.

Evidence for dual adrenergic receptor regulation of ovine pineal function.

Both alpha 1- and beta-adrenergic receptors are present on ovine pineals. In the rat these two receptors interact so that activation of the alpha 1-receptor potentiates the beta-receptor-mediated changes in cyclic AMP and the correlated changes in pineal N-acetyltransferase (EC 2.3.1.87). Here we investigate possible interactions between alpha 1- and beta-receptors through changes in cyclic AMP and assess the importance of each receptor to the melatonin response in ovine pineal punches/slices in vitro. The adrenergic agonists isoproterenol (ISO), noradrenaline (NA), and phenylephrine (PHE) stimulated dose-dependent changes in cyclic AMP with the order of potency of ISO greater than NA greater than PHE, consistent with their relative binding affinities for the beta-receptor. The beta-receptor antagonist, propranolol, showed dose-dependent inhibition of the ISO effect, whereas the alpha 1-selective antagonist, prazosin, had no effect. The S-shape of the stimulation and inhibition curves for ISO reflects cyclic AMP changes mediated by the beta-receptor only without interaction through the alpha 1-receptor. Each of the adrenergic agonists stimulated indistinguishable dose-dependent increases in melatonin release. The ability of PHE to stimulate changes in melatonin release in the absence of concomitant changes in cyclic AMP indicates an important role for the alpha 1-receptor. Prazosin inhibits this response, substantiating this conclusion. However, as propranolol is also inhibitory, it seems that the alpha 1-receptor response is absolutely dependent upon a small level of beta-receptor stimulation, thus providing evidence for adrenergic receptor interaction at a step other than cyclic AMP.

Neuropeptide Y (NPY) innervation of the ovine pineal gland.

A dense network of neuropeptide Y (NPY)-like immunoreactive (NPY-LI) fibres was revealed in the ovine pineal gland at the light microscope level. The dorsal and peripheral regions of the gland contained the most dense concentration of NPY-LI fibres with relatively few fibres in the mid-region and almost none in the pineal stalk. The effect of NPY in conjunction with isoproterenol (ISO) on cyclic AMP (cAMP) accumulation and noradrenaline (NA) on melatonin synthesis was investigated using in vitro techniques. NPY had no effect on the stimulation of cAMP or melatonin synthesis by the adrenergic agonists.

Culture conflict and coping in a group of aboriginal adolescents.

Critical incidents adapted to presentation in picture form were used to investigate responses of Aboriginal adolescents from Elcho Island mission in the Northern Territory of Australia in conflict situations arising from culture contact. These Aboriginal youths are part of a complex environment where choice behaviour is mediated by specific and broader situational characteristics of the social environment. Results showed a relationship between conflict responses and orientation to traditional values and skills, but no apparent relationship between conflict responses and modern value orientation or psychopathology variables. Adolescents who attended high school in Darwin were seen as more mission and academically oriented than locally educated youth. Contary to expected patterns, males appeared to be less involved in both mission and traditional activities and more restricted by traditional social expectations than were females.