title: Extracellular acidification at the surface of depolarized voltage-clamped snail neurones detected with eccentric combination pH microelectrodes.
abstract: A new design of double micropipette was used to measure intracellular pH, membrane potential, and surface pH of superfused snail neurones. A third double micropipette was used to control the membrane potential via a CsCl-filled barrel and inject HCl iontophoretically. In one series of experiments the surface pH fell by up to one-third of a pH unit when the membrane potential was clamped to 20 mV, pHi was initially 6.7, and extracellular pH was about 7.4 in a medium buffered either with 2 mM HEPES or 2.7% CO2 and 20 mM bicarbonate. In a second series in which surface pH was observed during brief depolarizations to different potentials with different pHi, the potential at which the surface began to acidify varied with pHi with a slope of 32 mV per pH unit. The results confirm that H+ ions leave depolarized snail neurones if the electrochemical gradient is favourable and show that CO2-bicarbonate buffered solutions have a low effective extracellular buffering power for rapid additions of acid.
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D005110:Extracellular Space / Q000378:metabolism / Q000502:physiology*; D006531:HEPES / Q000494:pharmacology; D006372:Helix, Snails; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*
chemical_list: D006531:HEPES