Abstract
The intracellular pH (pHi) of squid giant axons has been measured using glass pH microelectrodes. Resting pHi in artificial seawater (ASW) (pH 7.6-7.8) at 23 degrees C was 7.32 +/- 0.02 (7.28 if corrected for liquid junction potential). Exposure of the axon to 5% CO2 at constant external pH caused a sharp decrease in pHi, while the subsequent removal of the gas caused pHi to overshoot its initial value. If the exposure to CO2 was prolonged, two additional effects were noted: (a) during the exposure, the rapid initial fall in pHi was followed by a slow rise, and (b) after the exposure, the overshoot was greatly exaggerated. Application of external NH4Cl caused pHi to rise sharply; return to normal ASW caused pHi to return to a value below its initial one. If the exposure to NH4Cl was prolonged, two additional effects were noted: (a) during the exposure, the rapid initial rise in pHi was followed by a slow fall, and (b) after the exposure, the undershoot was greatly exaggerated. Exposure to several weak acid metabolic inhibitors caused a fall in pHi whose reversibility depended upon length of exposure. Inverting the electrochemical gradient for H+ with 100 mM K- ASW had no effect on pHi changes resulting from short-term exposure to azide. A mathematical model explains the pHi changes caused by NH4Cl on the basis of passive movements of both NH3 and NH4+. The simultaneous passive movements of CO2 and HCO3-cannot explain the results of the CO2 experiments; these data require the postulation of an active proton extrusion and/or sequestration mechanism.
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Selected References
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- Bicher H. I., Oki S. Intracellular pH electrode. Experiments on the giant squid axon. Biochim Biophys Acta. 1972 Mar 17;255(3):900–904. doi: 10.1016/0005-2736(72)90401-4. [DOI] [PubMed] [Google Scholar]
- Brinley F. J., Jr, Mullins L. J. Sodium extrusion by internally dialyzed squid axons. J Gen Physiol. 1967 Nov;50(10):2303–2331. doi: 10.1085/jgp.50.10.2303. [DOI] [PMC free article] [PubMed] [Google Scholar]
- CALDWELL P. C. An investigation of the intracellular pH of crab muscle fibres by means of micro-glass and micro-tungsten electrodes. J Physiol. 1954 Oct 28;126(1):169–180. doi: 10.1113/jphysiol.1954.sp005201. [DOI] [PMC free article] [PubMed] [Google Scholar]
- CALDWELL P. C., KEYNES R. D. The permeability of the squid giant axon to radioactive potassium and chloride ions. J Physiol. 1960 Nov;154:177–189. doi: 10.1113/jphysiol.1960.sp006572. [DOI] [PMC free article] [PubMed] [Google Scholar]
- COLE K. S., MOORE J. W. Liquid junction and membrane potentials of the squid giant axon. J Gen Physiol. 1960 May;43:971–980. doi: 10.1085/jgp.43.5.971. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Carter N. W., Rector F. C., Jr, Campion D. S., Seldin D. W. Measurement of intracellular pH of skeletal muscle with pH-sensitive glass microelectrodes. J Clin Invest. 1967 Jun;46(6):920–933. doi: 10.1172/JCI105598. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Howell B. J., Baumgardner F. W., Bondi K., Rahn H. Acid-base balance in cold-blooded vertebrates as a function of body temperature. Am J Physiol. 1970 Feb;218(2):600–606. doi: 10.1152/ajplegacy.1970.218.2.600. [DOI] [PubMed] [Google Scholar]
- McLaughlin S. G., Hinke J. A. Optical density changes of single muscle fibres in sodium-free solutions. Can J Physiol Pharmacol. 1968 Mar;46(2):247–260. doi: 10.1139/y68-041. [DOI] [PubMed] [Google Scholar]
- ORLOFF J., BERLINER R. W. The mechanism of the excretion of ammonia in the dog. J Clin Invest. 1956 Feb;35(2):223–235. doi: 10.1172/JCI103267. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Reeves R. B. An imidazole alphastat hypothesis for vertebrate acid-base regulation: tissue carbon dioxide content and body temperature in bullfrogs. Respir Physiol. 1972 Mar;14(1):219–236. doi: 10.1016/0034-5687(72)90030-8. [DOI] [PubMed] [Google Scholar]
- Roos A. Intracellular pH and buffering power of rat muscle. Am J Physiol. 1971 Jul;221(1):182–188. doi: 10.1152/ajplegacy.1971.221.1.182. [DOI] [PubMed] [Google Scholar]
- Roos A. Intracellular pH and intracellular buffering power of the cat brain. Am J Physiol. 1965 Dec;209(6):1233–1246. doi: 10.1152/ajplegacy.1965.209.6.1233. [DOI] [PubMed] [Google Scholar]
- SPYROPOULOS C. S. Cytoplasmic pH of nerve fibres. J Neurochem. 1960 Feb;5:185–194. doi: 10.1111/j.1471-4159.1960.tb13352.x. [DOI] [PubMed] [Google Scholar]
- Thomas R. C. Intracellular pH of snail neurones measured with a new pH-sensitive glass mirco-electrode. J Physiol. 1974 Apr;238(1):159–180. doi: 10.1113/jphysiol.1974.sp010516. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Thomas R. C. Proceedings: The effect of bicarbonate on the intracellular buffering power of snail neurones. J Physiol. 1974 Sep;241(2):103P–104P. [PubMed] [Google Scholar]