| Abstract
| - Objective: The aim was to demonstrate that removal of extracellular sodium (Na+o), a manoeuvre known to increase intracellular calcium (Ca2+i), can activate a chloride ion conductance in cultured embryonic chick heart cells. Methods: Intracellular chloride activity (aiCl) and membrane potentials (Em) were simultaneously measured using chloride selective and 3 M KCl filled microelectrodes. Results: In Na+o-free and K+o-free solutions, a frusemide (0.3 mM) resistant decrease in a of 10 mM was recorded within 10 min, along with a 5 mV hyperpolarisation, and the calculated chloride equilibrium potential (ECl) followed the change of Em, suggesting a possibly enhanced chloride conductance. When cells were exposed to Na+o-free solution, the decrease of aiCl by ∼10 mM was associated with an initial depolarisation, followed by a hyperpolarisation to ∼−60 mV (more negative than ECl). Subsequent removal of K+o depolarised Em to −39 mV (≈ECl), and no further loss of aiCl, occurred. Restoration of K+o caused a hyperpolarisation of Em (more negative than ECl) and a continuing decline of aciCl. Prevention of K+o induced hyperpolarisation by addition of 1 mM Ba2+ stopped the decline of aiCl (Em ≈ECl), suggesting that following Na removal, alteration of the driving force for chloride led to a chloride efflux via an enhanced chloride conductance. When Em depolarised to −50 mV after 3 min exposure to 0.1 mM ouabain, removal of [Cl−]o caused a further depolarisation and readdition of [Cl−]o induced an 18 mV hyperpolarisation. This chloride induced hyperpolarisation was blocked by removal of [Ca2+]0 (+1 mM EGTA). Conclusions: The increase in chloride conductance observed under conditions that are known to raise Ca2+i supports the presence of a Ca2+i activated chloride conductance in cultured chick heart cells. Cardiovascular Research 1994;28:1629-1634
|
