Maintenance of quantal size and immediately releasable granules in rat chromaffin cells by glucocorticoid

Protective effect of arachidonic acid and linoleic acid on 1-methyl-4-phenylpyridinium-induced toxicity in PC12 cells

Background

Parkinson’s disease is a neurodegenerative disorder that is being characterized by the progressive loss of dopaminergic neurons of the nigrostriatal pathway in the brain. The protective effect of omega-6 fatty acids is unclear. There are lots of contradictions in the literature with regard to the cytoprotective role of arachidonic acid. To date, there is no solid evidence that shows the protective role of omega-6 fatty acids in Parkinson’s disease. In the current study, the potential of two omega-6 fatty acids (i.e. arachidonic acid and linoleic acid) in alleviating 1-methyl-4-phenylpyridinium (MPP⁺)-induced cytotoxicity in PC12 cells was examined.

Methods

Cultured PC12 cells were either treated with MPP⁺ alone or co-treated with one of the omega-6 fatty acids for 1 day. Cell viability was then assessed by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

Results

Cells treated with 500 μM MPP⁺ for a day reduced cell viability to ~70% as compared to control group. Linoleic acid (50 and 100 μM) significantly reduced MPP⁺-induced cell death back to ~85-90% of the control value. The protective effect could be mimicked by arachidonic acid, but not by ciglitazone.

Conclusions

Both linoleic acid and arachidonic acid are able to inhibit MPP⁺-induced toxicity in PC12 cells. The protection is not mediated via peroxisome proliferator-activated receptor gamma (PPAR-γ). Overall, the results suggest the potential role of omega-6 fatty acids in the treatment of Parkinson’s disease.

Increased catecholamine secretion from single adrenal chromaffin cells in DOCA-salt hypertension is associated with potassium channel dysfunction

The mechanism of catecholamine release from single adrenal chromaffin cells isolated from normotensive and DOCA-salt hypertensive rats was investigated. These cells were used as a model for sympathetic nerves to better understand how exocytotic release of catecholamines is altered in this model of hypertension. Catecholamine secretion was evoked by local application of acetylcholine (1 mM) or high K+ (70 mM), and continuous amperometry was used to monitor catecholamine secretion as an oxidative current. The total number of catecholamine molecules secreted from a vesicle, the total number of vesicles fusing and secreting, and the duration of secretion in response to a stimulus were all significantly greater for chromaffin cells from hypertensive rats as compared to normotensive controls. The greater catecholamine secretion from DOCA-salt cells results, at least in part, from functionally impaired large conductance, Ca2+-activated (BK) and ATP-sensitive K+ channels. This work reveals that there is altered vesicular release of catecholamines from these cells (and possibly from perivascular sympathetic nerves) and this may contribute to increased vasomotor tone in DOCA-salt hypertension.

Influence of cholesterol on catecholamine release from the fusion pore of large dense core chromaffin granules

Changes in cellular cholesterol can affect exocytosis, but the influence of cholesterol in fusion pore kinetics is unclear. Using carbon fiber amperometry, we monitored quantal catecholamine release from rat chromaffin cells. To bypass any possible effect of cholesterol perturbation on ion channels or the colocalization of voltage-gated Ca(2+) channels with sites of exocytosis, exocytosis was stimulated via uniform elevation of cytosolic [Ca(2+)] (with whole-cell dialysis of a Ca(2+)-buffered solution). Under this condition, alterations of cellular cholesterol affected neither the mean number of amperometric events triggered per cell nor their quantal size and the kinetics of their main spike (which reflects the rapid release during and after rapid fusion pore dilation). In contrast, the reduction of cellular cholesterol shortened the "prespike foot" signals (which reflect the leakage of catecholamine via a semi-stable fusion pore) and reduced the proportion of "stand-alone foot" signals (which reflect the release via a flickering fusion pore that may close before it dilates significantly), whereas an oversupply of cholesterol had opposite effects. Acute extraction of cholesterol from the cytosol (via whole-cell dialysis of a cholesterol extractor) also shortened the prespike foot signals and reduced the proportion of stand-alone foot signals, but acute extracellular application of cholesterol extractor or "soluble" cholesterol had no effect. Our data raise the possibility that cholesterol molecules, particularly those in the cytoplasmic leaflet, helps to constrain the narrow waistline of a semi-stable fusion pore while it is flickering or before it starts to dilate rapidly.

Measuring secretion in chromaffin cells using electrophysiological and electrochemical methods

Our present understanding of exocytosis of catecholamines has benefited tremendously from the arrival of single-cell electrochemical methods (amperometry and voltammetry), electrophysiological techniques (whole-cell and patch capacitance) and from the combination of both techniques (patch amperometry). In this brief review, we will outline the strengths and limitations of amperometric and electrophysiological methods and highlight the major contribution obtained with the use of these techniques in chromaffin cells.