title: Changes in the intracellular free calcium concentration of Aplysia and leech neurones measured with calcium-sensitive microelectrodes.
abstract: The intracellular free Ca concentration was measured in invertebrate neurones using single-barrelled and double-barrelled neutral-carrier microelectrodes. The electrodes were calibrated in solutions containing different Ca concentrations between 1 mM and 0.01 microM. The electrode responses were also tested at different ionic strengths and at varying Na concentrations. The electrodes responded with 25-30 mV per 10-fold change in Ca concentration between 1 mM and 1 microM and with 10-25 mV between 1 and 0.1 microM Ca. The intracellular free Ca concentration was measured to be between 0.1 and 0.7 microM in the neurones. The changes of intracellular Ca in identified voltage-clamped neurones of Aplysia californica were recorded during iontophoretic injections of Ca2+ or EGTA. The decrease of intracellular Ca following EGTA injection was correlated with the suppression of the Ca-dependent K current and with the reduction of Ca-induced inactivation of voltage-dependent Ca current. In identified neurones of the leech Hirudo medicinalis a reversible increase of intracellular Ca2+ was recorded after inhibition of the Na-K pump, either by addition of ouabain (0.5 mM) or by lowering the external K concentration (0.2 mM). This rise in intracellular Ca2+ did not occur, and was even reversed, in the absence of external Na, suggesting the existence of Na-Ca exchange across the leech neuronal membrane.
mesh_terms: D000818:Animals; D001048:Aplysia; D001826:Body Fluids / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism*; D007865:Leeches; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009474:Neurons / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology
chemical_list: D004533:Egtazic Acid; D010042:Ouabain; D002118:Calcium