title: Ability of the Ca2+-selective microelectrodes to measure fast and local Ca2+ transients in nerve cells.
abstract: The ability of the Ca2+-selective microelectrode to measure fast Ca2+ transients intracellularly is reviewed. In vitro, Ca microelectrodes can respond to Ca2+ injections with time to peaks as small as 40 ms. We present methods to improve the dynamic response of Ca microelectrodes and to make Ca-buffered solutions in high ionic strength. Examples of measurements of intracellular free Ca2+ [( Ca2+]i) transients in Aplysia neurons and in Limulus photoreceptors are shown. To show the validity of those measurements, simultaneous recordings of the Arsenazo III (AIII) absorbance and of the Ca-selective electrode potential were made in voltage-clamped neurons of the abdominal ganglion of Aplysia californica. Pressure injection of AIII to a concentration of 300-500 microM induced a rise in resting [Ca2+]i; injection of higher [AIII] led to buffering of [Ca2+]i transients. Both techniques responded to changes in resting [Ca2+]i in the same direction except that AIII showed an increase in absorbance in 0 [Ca2+]o. Voltage-clamp pulses transiently increased both the AIII absorbance and the Ca2+ electrode potential. Reducing or increasing the driving force for Ca2+ entry changed the magnitude of both signals in the right direction. Examples of spatial localization of [Ca2+]i increases and Ca2+ gradients within the cytoplasm were demonstrated using the Ca electrode. The use of optical techniques to measure local [Ca2+]i changes is briefly reviewed.
mesh_terms: D000818:Animals; D001150:Arsenazo III / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004563:Electrochemistry / Q000295:instrumentation*; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*
chemical_list: D007473:Ion Channels; D001150:Arsenazo III; D002118:Calcium