Developmental changes in hyperpolarization-activated currents I(h) and I(K(IR)) in isolated rat intracardiac neurons.
The hyperpolarization-activated nonselective cation current, I(h), was investigated in neonatal and adult rat intracardiac neurons. I(h) was observed in all neurons studied and displayed slow time-dependent rectification. I(h) was isolated by blockade with external Cs(+) (2 mM) and was inhibited irreversibly by the bradycardic agent, ZD 7288. Current density of I(h) was approximately twofold greater in neurons from neonatal (-4.1 pA/pF at -130 mV) as compared with adult (-2.3 pA/pF) rats; however, the reversal potential and activation parameters were unchanged. The reversal potential and amplitude of I(h) was sensitive to changes in external Na(+) and K(+) concentrations. An inwardly rectifying K(+) current, I(K(IR)), was also present in intracardiac neurons from adult but not neonatal rats and was blocked by extracellular Ba(2+). I(K(IR)) was present in approximately one-third of the adult intracardiac neurons studied, with a current density of -0.6 pA/pF at -130 mV. I(K(IR)) displayed rapid activation kinetics and no time-dependent rectification consistent with the rapidly activating, inward K(+) rectifier described in other mammalian autonomic neurons. I(K(IR)) was sensitive to changes in external K(+), whereby raising the external K(+) concentration from 3 to 15 mM shifted the reversal potential by approximately +36 mV. Substitution of external Na(+) had no effect on the reversal potential or amplitude of I(K(IR)). I(K(IR)) density increases as a function of postnatal development in a population of rat intracardiac neurons, which together with a concomitant decrease in I(h) may contribute to changes in the modulation of neuronal excitability in adult versus neonatal rat intracardiac ganglia.
Hogg
R C
RC
School of Biomedical Sciences, Department of Physiology and Pharmacology, University of Queensland, Brisbane, Queensland 4072, Australia.
Harper
A A
AA
Adams
D J
DJ
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002316:Cardiotonic Agents / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity; D005726:Ganglia, Parasympathetic / Q000166:cytology* / Q000254:growth & development*; D006321:Heart / Q000294:innervation*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000493:pharmacokinetics; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D013696:Temperature
D002316:Cardiotonic Agents; D011743:Pyrimidines; C082246:ICI D2788; D002586:Cesium; D011188:Potassium