Regulation of A‐currents by cell‐cell interactions and neurotrophic factors in developing chick parasympathetic neurones.

Abstract

1. The developmental regulation of ion channel expression was studied in parasympathetic neurones isolated from the chick ciliary ganglion. Whole-cell patch clamp recordings were made from ciliary ganglion neurones that were removed from the embryo on the ninth embryonic day (E9) and maintained in dissociated cell culture for an additional 4 days. Previous studies have shown that the expression of a transient voltage-activated K+ current (IA) is regulated by unidentified environmental stimuli during these developmental stages. 2. The effect of interactions between neurones and target tissue on the expression of IA was tested by co-culturing ciliary ganglion neurones with chick striated muscle cells.Neurones from the nerve-muscle co-cultures expressed normal amplitudes of IA, but the neurones did not express normal levels of IA when they were plated onto lysed muscle fibres. 3. The effect of interactions between ganglionic neurones and non-neuronal ganglionic cells was tested by culturing ganglia as explants rather than as dissociated cells. Neurones isolated from the explant cultures did not express normal levels of IA. Similarly, when dissociated ganglionic neurones were co-cultured with fibroblasts isolated from embryonic chick skin, they did not express normal amplitudes of IA. 4. Chronic depolarization caused by growing ciliary ganglion neurones in the presence of elevated K+ concentrations did not allow for the normal expression of IA, although it did promote the survival of these neurones in vitro.5. Addition of 40 ng ml-of recombinant human ciliary neurotrophic factor (CNTF) or basic fibroblast growth factor (bFGF) to the cell culture medium had no effect on IA expression in developing chick ciliary ganglion neurones. However, 40 ng ml' of acidic fibroblast growth factor (aFGF) stimulated the expression of IA. All trophic factors promoted the growth and survival of ciliary ganglion neurones in vitro. 6. Dissociated ciliary ganglion neurones were maintained in a culture medium containing an aqueous extract of the whole brain. Neurones developing under these conditions expressed normal levels of IA. The stimulatory activity of the brain extract was destroyed by heating. 7. The expression of IA in chick ciliary ganglion neurones developing in vitro can be regulated by soluble growth factors and by interactions with certain other cell types. Similar interactions may regulate the expression of IA in ciliary ganglion neurones developing in situ.

ERK/MAPK regulates the Kv4.2 potassium channel by direct phosphorylation of the pore-forming subunit

“…The present studies implicate the Kv4.2 voltage-dependent K ϩ channel as a direct target of ERK. In the context of neuronal development and differentiation as well as disease processes, direct ERK/MAPK phosphorylation of Kv4 channel subunits presents a possible mechanism for the acute regulation of K ϩ currents by growth factors, as has been previously reported (12,49).…”

Neuregulins stimulate the functional expression of Ca 2+ -activated K + channels in developing chicken parasympathetic neurons

“…Chicken CG neurons were isolated at embryonic day 9 (E9) and cultured as described previously in a medium containing 40 ng⅐ml Ϫ1 recombinant rat ciliary neurotrophic factor (CNTF) (29,30,34). Cells were maintained in vitro for 12 hr in the presence or absence of erbB ligands or other factors.…”

A-Current Expression is Regulated by Activity but not by Target Tissues in Developing Lumbar Motoneurons of the Chick Embryo

“…Similar developmental changes in I A density have been observed in other cell types (Dourado and Dryer 1992;McFarlane and Cooper 1992;Nerbonne et al 1986). A variety of mechanisms could trigger these changes, including a completely intrinsic program of channel expression (Dourado and Dryer 1992;Spitzer and Lamborghini 1976), regulation by cell-cell interactions via soluble Dourado and Dryer 1994;McFarlane and Cooper 1993;Subramony and Dryer 1997) or insoluble (Raucher and Dryer 1994;Wu and Barish 1994) regulatory factors, or regulation by activity (Baines et al 2001;Liu and Kaczmarek 1998;Martin-Caraballo and Dryer 2002a;Muller et al 1998).…”

“…The developmental expression of some types of channels proceeds according to an internal developmental program (Dourado and Dryer 1992;Spitzer and Lamborghini 1976), whereas expression of others appears to require neurotrophic interactions with other cell types, ongoing electrical activity, or both (reviewed in Dryer et al 2003). Although the precise spatiotemporal pattern of channel expression depends on the cell population being studied, the developmental expression of some channels, including Ca 2ϩ -activated K ϩ channels (I K(Ca) ) and A-type K ϩ channels (I A ), requires cell-cell interactions in several neuronal populations (Cameron et al , 1999(Cameron et al , 2001Dryer 1992, 1994;Dourado et al 1994;Martin-Caraballo and Dryer 2002a,b;Cooper 1992, 1993;Raucher andDryer 1994, 1995;Wu and Barish 1994).…”

“…An initial description of this process was carried out by McCobb et al (1990), who described the stage at which I A first appears and the trajectory of the increase in the functional expression of these channels during LMN development. Since then, a substantial body of literature has shown that trophic factors and cell-cell interactions can regulate developmental expression of I A Dourado et al 1994;McFarlane and Cooper 1993; Raucher and Dryer 1994). Therefore we have readdressed the issue of I A development in LMNs to determine cellular processes that regulate these channels.…”