S. Raucher et Se. Dryer, FUNCTIONAL EXPRESSION OF A-CURRENTS IN EMBRYONIC CHICK SYMPATHETIC NEURONS DURING DEVELOPMENT IN-SITU AND IN-VITRO, Journal of physiology, 479(1), 1994, pp. 77-93
1. The functional expression of transient voltage-activated K+ current
s (I-A) was examined using whole-cell recording techniques in embryoni
c chick sympathetic ganglion neurones that developed in situ and under
various growth conditions in vitro. 2. The density of I-A increased d
ramatically during development in sympathetic neurones isolated acutel
y between embryonic days 7 and 20 (E7-E20). The time course of I-A ina
ctivation became significantly faster between E7 and E13, With these p
rotocols, neuronal differentiation and development occurred entirely i
n situ. 3. Sympathetic neurones isolated at E9 and maintained in vitro
for 4 days did not express a normal I-A compared to neurones isolated
acutely at E13. Those neurones that were in physical contact with oth
er neurones expressed normal densities of I-A, but the resulting inact
ivation kinetics were abnormally slow. Sympathetic neurones that were
cultured on the membrane fragments of lysed neurones expressed normal
densities of I-A even when they failed to make visible connections wit
h other viable neurones, but the resulting inactivation kinetics were
abnormally slow. Those cultured neurones that were not in physical con
tact with other cells or their membranes had markedly reduced densitie
s of I-A with abnormally slow inactivation kinetics. 4. Application of
5-100 ng m1(-1) 2.5 S nerve growth factor by itself did not promote n
ormal I-A density or kinetics in E9 sympathetic neurones cultured for
4 days. 5. Sympathetic neurones that developed in vitro in physical co
ntact with ventral spinal cord explants, cardiac myocytes or aortic sm
ooth muscle cells expressed normal densities of I-A, but the inactivat
ion kinetics were abnormally slow. Cell culture media conditioned by t
hese tissues failed to promote normal I-A expression. Sympathetic neur
ones cultured as explants or maintained under depolarizing conditions
did not express a normal I-A. 6. Embryonic chick sympathetic neurones
exhibit developmental changes in the density and kinetics of I-A that
can be regulated independently by extrinsic environmental factors incl
uding interactions with insoluble components of the plasma membranes o
f some cells.