title: Intracellular calcium ions and calcium currents in perfused neurones of the snail, Lymnaea stagnalis.
abstract: Neuronal somata of Lymnaea stagnalis were internally perfused and voltage clamped using the suction pipette method. The cells were exposed to internal solutions buffered to various concentrations of Ca2+ while the cytoplasmic Ca2+ activity [( Ca2+]i) was monitored with a Ca2+ -sensitive micro-electrode. [Ca2+]i was usually about 10(-7) M when the cell was perfused with a solution buffered to any level of Ca2+ from 9 X 10(-7) to below 10(-8) M. With internal solutions buffered to 10(-6) M-Ca2+ or greater, [Ca2+]i increased rapidly and overshot the perfusate Ca2+ activity by up to two orders of magnitude. It was thus virtually impossible to hold [Ca2+]i steady at any levels other than about 10(-7) M or 10(-4) M using internal perfusion of simple ionic internal solutions. The excess Ca2+ which caused the overshoot of [Ca2+]i entered the cell from the external solution through Cd2+ -sensitive channels. Cd2+ in the external solution prevented or reversed the overshoot of [Ca2+]i and brought [Ca2+]i to near the perfusate level. ATP added to the internal solution also prevented [Ca2+]i from overshooting the perfusate level during perfusion with high-Ca2+ buffers. By monitoring [Ca2+]i with a Ca2+ -sensitive micro-electrode, we were able to estimate the relationship between [Ca2+]i and the Ca2+ current (ICa) measured under voltage clamp. ICa was completely blocked as [Ca2+]i was raised to 10(-6) M. We believe that the discrepancy between our data and other estimates of the ICa vs. [Ca2+]i relationship using internal perfusion of molluscan nerve cells results from the incorrect assumption that [Ca2+]i is controlled adequately during internal perfusion.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005724:Ganglia / Q000166:cytology; D066298:In Vitro Techniques; D008195:Lymnaea; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors
chemical_list: D002614:Chelating Agents; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D004492:Edetic Acid; C026060:N-(hydroxyethyl)ethylenediaminetriacetic acid; D002118:Calcium