Perinatal changes of I(h) in phrenic motoneurons.
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.
Di Pasquale
E
E
ESA CNRS 6034, Faculté des Sciences de St Jérôme, 13397 Marseille cedex 20, France. eric.di-pasquale@neurosciences.u-3mrs.fr
Tell
F
F
Ptak
K
K
Monteau
R
R
Hilaire
G
G
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
D002317:Cardiovascular Agents; D011743:Pyrimidines; C082246:ICI D2788; D002586:Cesium