Neonatal chromaffin cells

Developmentally, the best characterized cell lineage within the neural crest is probably the sympathoadrenal lineage. There are three cell types in this lineage, the sympathetic neuron, the adrenal chromaffin cell and a third cell of an intermediate phenotype, the so called small, intensely fluorescent cell (SIF cell) (see Anderson, 1989 Patterson, 1990). Although progenitors of this lineage have not been isolated from neural crest cultures, they have have been isolated from embryonic adrenal medulla as well as from both embryonic and neonatal sympathetic ganglia. 

A number of reports suggest that FGF-2 not only affects developmental differentiation of neurons but also stabilizes the mature neuronal phenotype. Examples are the ability of FGF-2 to maintain neurotransmitter stores in cultured neonatal chromaffin cells without inducing transmitter-synthesizing enzymes (Unsicker and Westermann,... 

Thompson RJ, Nurse CA. Anoxia differentially modulates multiple K" " currents and depolarizes neonatal rat adrenal chromaffin cells. J Physiol 1998 512 421—434. 

Oxygen Sensing by Neonatal Adrenal Chromaffin Cells... 

Figure 1 Effects of hypoxia on whole-cell K+ current in neonatal rat chromaffin cells, (a) Ramp I-V relation showing suppression of outward K+ current by hypoxia (h PO2 10 torr) at positive potentials normoxic I-V relation is indicated by control (c) trace. In (b) the hypoxia-sensitive component is shown as a difference current (trace c-trace h). In (b) note reversal of this hypoxia-sensitive current near the K equilibrium potential (Ek — 83 mV). Voltage-dependent Na currents were blocked with tetrodotoxin in this experiment.

III. Does Mitochondrial Inhibition Mimic Hypoxic Regulation of 02-Sensitive Voltage-Dependent Currents in Neonatal Chromaffin Cells ... 

Figure 2 Effects of inhibitors of the mitochondrial electron transport chain on outward K" " current in neonatal rat chromaffin cells. Representative traces for a voltage step to +30 mV are shown on the left, for a variety of inhibitor concentrations as indicated in (a) cyanide, (b) 2,4-dinitrophenol (DNP), and (c) rotenone. The corresponding I-V relation for each cell is shown on the right. Note that both cyanide and DNP had no effect, whereas rotenone caused a dose-dependent inhibition of outward K+ current.

Figure 4 Properties of single versus clustered neonatal rat chromaffin cells, (a) T3Tosine hydroxylase (TH)-positive immunofluorescence of chromaffin cells in culture note the presence of small clusters and occasional single isolated cells. Perforated-patch recordings of membrane potential revealed that single cells tended to he quiescent (h), whereas cells in clusters tended to fire spontaneous action potentials at room temperatine (c).

VI. Role of 02-Sensltlve BK Channels in Catecholamine Secretion from Neonatal Chromaffin Cells... 

K" " does not mimic the same secretory pattern induced by hypoxia, whereas inhibition of BK charmels does. They further caution against a total reliance on generalized amine secretion as a measure of the true hypoxic response, and emphasize that the pattern of stimulation (phasic vs. tonic) may be an important determinant of the proportion of the individual CA secreted. Taken together, these data strongly support an important role for the inhibition of BK channels in the hypoxic chemosensitivity of neonatal rat chromaffin cells. 

The mechanisms by which hypoxia regulates BK and other 02-sensitive K channels in neonatal chromaffin cells are not completely imderstood. These mechanisms are also relevant to neonatal rat CB type 1 cells (42) and neocortical neurons (43) where hypoxic regulation of BK channels did not occiu in excised patches, presumably owing to loss of cytoplasmic factors. This view was recently challenged in adult rat type 1 cells, where hypoxic regulation of BK channels was observed in inside-out patches and was proposed to occur by a membrane-delimited mechanism (44). While the reason for this discrepancy is imknown and may be age-related, the possibility that intracellular organelles (e.g., mitochondria) might remain attached to membrane patches after excision cannot be excluded (45). 

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