Ionic basis of the membrane potential responses of rat dorsal vagal motoneurones to HEPES buffer.
The effects of 10 mM HEPES (N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid) buffered artificial cerebrospinal fluid (aCSF) on membrane potential and the action potential were studied in 93 dorsal vagal motoneurones (DVMs) using an in vitro slice preparation of the rat medulla. Changing from bicarbonate/CO2 aCSF to HEPES aCSF resulted in a depolarisation of 6.0 +/- 0.6 mV and an increase in input resistance (RIn; n = 61). In the presence of 5 mM 4-AP, HEPES either had little effect (n = 9) or hyperpolarised the membrane (n = 10). Mn2+ (3 mM) or Ni2+ (200 microM) abolished the hyperpolarisation and its associated increase in RIn. In voltage-clamp studies 5 mM 4-AP eliminated a transient outward current and Ni2+ blocked an inactivating inward current. It is concluded that HEPES buffer reduces the contribution of the A current to resting membrane potential and also reduces a Ni(2+)-sensitive transient ICa.
Cowan
A I
AI
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australia.
Martin
R L
RL
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002555:Cerebrospinal Fluid; D004594:Electrophysiology; D006531:HEPES / Q000494:pharmacology*; D017136:Ion Transport / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D014630:Vagus Nerve / Q000166:cytology* / Q000502:physiology
D001639:Bicarbonates; D015220:Calcium Channels; D015221:Potassium Channels; D009532:Nickel; D015761:4-Aminopyridine; D008274:Magnesium; D011188:Potassium; D006531:HEPES; D002118:Calcium