title: Perinatal changes of I(h) in phrenic motoneurons.
abstract: The hyperpolarization-activated cationic current (I(h)) was characterized and its maturation studied on phrenic motoneurons (PMNs), from reduced preparations of foetal (E18 and E21) and newborn (P0-P3) rats, using the whole-cell patch-clamp technique. In voltage-clamp mode, 2-s hyperpolarizing steps (5-mV, -50 to -110 mV) elicited a noninactivating inward current, blocked by external application of Cs+ or ZD 7288. At -110 mV, Ih current density averaged 0.67 +/- 0.41 pA/pF at E18, reached a transient peak at E21 (1.38 +/- 0.11 pA/pF) and decreased at P0-P3 (0.77 +/- 0.22 pA/pF). V1/2 was similar at E18 and E21 (-79 mV) but was significantly hyperpolarized at P0-P3 (-90 mV). The time constant of activation was voltage-dependent, and significantly faster at E21. Reversal potential was similar at all ages when estimated by extrapolation or tail current procedures. It was positively shifted by 25 +/- 6 mV when external potassium was raised from 3 to 10 m M, suggesting a similar sensitivity to K+ from E18 to P0-3. Cs(+) or ZD 7288 applications on PMNs at rest in current-clamp mode, in a partitioned chamber, induced a 10 +/- 2 mV hyperpolarization at E18 and E21, and an 8 +/- 2 mV hyperpolarization at P0-3. The area of the central respiratory drive potential or current was increased by 33 and 31%, respectively, at E21, but was not significantly modified at E18 and P0-3. Our data suggest a critical period during the perinatal maturation of Ih during which it is transiently upregulated and attenuates the influence of the central respiratory drive on PMNs just prior to birth.
authors: ESA CNRS 6034, Faculté des Sciences de St Jérôme, 13397 Marseille cedex 20, France. eric.di-pasquale@neurosciences.u-3mrs.fr
authors: E
authors: E
authors: Di Pasquale
authors: F
authors: F
authors: Tell
authors: K
authors: K
authors: Ptak
authors: R
authors: R
authors: Monteau
authors: G
authors: G
authors: Hilaire
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002317:Cardiovascular Agents / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D005333:Fetus / Q000166:cytology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010791:Phrenic Nerve / Q000166:cytology / Q000254:growth & development / Q000502:physiology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012125:Respiratory Center / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000294:innervation
chemical_list: D002317:Cardiovascular Agents; D011743:Pyrimidines; C082246:ICI D2788; D002586:Cesium