Ecdysteroid control of ionic current development in Manduca sexta motoneurons.
The steroid hormone 20-hydroxyecdysone (20-HE) regulates several processes during insect metamorphosis. We studied the effects of 20-HE on the development of voltage-sensitive ionic currents of thoracic leg motoneurons of Manduca sexta. The larval leg motoneurons persist throughout metamorphosis but undergo substantial morphological reorganization, which is under the control of 20-HE and accompanied by changes in Ca2+ and K+ current densities. To determine whether 20-HE controls the changes in Ca2+ and K+ current levels during postembryonic development, identified thoracic leg motoneurons isolated from late larval and early pupal stages were taken into primary cell culture. Whole-cell Ca2+ and K+ currents were measured after 1-4 days of steroid hormone incubation. In the presence of 20-HE, peak Ca2+ currents of pupal leg motoneurons increased from day 1 to day 4 in vitro. Thus, at culture day 4 the pupal Ca2+ current levels were larger in 20-HE-treated than in untreated cells. By contrast, 20-HE did not affect the Ca2+ current amplitudes of larval leg motoneurons. Whole-cell K+ currents, measured at 4 days in pupal motoneurons, consisted of a fast-activating transient current and a sustained, slowly inactivating current. 20-HE did not affect the amplitude of the transient or sustained currents after 4 days in vitro. Thus, a direct steroid hormone effect may control the proper maturation of voltage-sensitive Ca2+ currents in leg motoneurons.
Grünewald
B
B
Institut für Neurobiologie, FU-Berlin, Germany.
Levine
R B
RB
D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D026461:Ecdysteroids; D005121:Extremities; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000502:physiology; D007301:Insect Hormones / Q000502:physiology; D018402:Manduca / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D008675:Metamorphosis, Biological; D009046:Motor Neurons / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D013256:Steroids / Q000502:physiology; D013909:Thorax
D015220:Calcium Channels; D026461:Ecdysteroids; D007301:Insect Hormones; D015221:Potassium Channels; D013256:Steroids