Perinatal changes of I(h) in phrenic motoneurons

• Published in: The European journal of neuroscience Vol. 13; no. 7; pp. 1403 - 1410
• Main Authors: Di Pasquale, E, Tell, F, Ptak, K, Monteau, R, Hilaire, G
• Format: Journal Article
• Language: English
• Published: France Wiley 01.04.2001
• Subjects: Animals; Animals, Newborn; Biochemistry; Biochemistry, Molecular Biology; Cardiovascular Agents; Cardiovascular Agents - pharmacology; Cesium; Cesium - pharmacology; Fetus; Fetus - cytology; Life Sciences; Membrane Potentials; Membrane Potentials - drug effects; Membrane Potentials - physiology; Motor Neurons; Motor Neurons - physiology; Patch-Clamp Techniques; Phrenic Nerve; Phrenic Nerve - cytology; Phrenic Nerve - growth & development; Phrenic Nerve - physiology; Pyrimidines; Pyrimidines - pharmacology; Rats; Rats, Sprague-Dawley; Respiratory Center; Respiratory Center - cytology; Respiratory Center - drug effects; Respiratory Center - growth & development; Respiratory Mechanics; Respiratory Mechanics - physiology; Respiratory Muscles; Respiratory Muscles - innervation
• ISSN: 0953-816X; 1460-9568

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.