J Zhang1, M Lieberman. 1. Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.
Abstract
OBJECTIVE: The aim was to apply various maneuvers to perturb the volume of cultured chick cardiac myocytes and to evaluate the association between the swelling-activated chloride conductance and membrane distention. METHODS: Swelling of single chick heart cells was induced by (1) reduction of external osmolarity; (2) elevation of intracellular osmolarity; (3) isosmotic urea uptake; and (4) positive pressure injection. Changes in cell volume and whole-cell currents were recorded simultaneously and a comparison among differently activated whole-cell currents was made in terms of time course, reversal potential (Erev), whole-cell conductance, and response to a number of channel blockers. RESULTS: Although the time course of cell swelling varied between the different experimental maneuvers, the resultant whole-cell current displayed nearly identical current-voltage relationships: outward rectification and a reversal potential near the calculated chloride equilibrium potential (ECl). The induced currents were inhibited by Cl- channel blockers, diphenylamine-2-carboxylate (DPC) and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), and were almost completely suppressed by gadolinium. In addition, the Cl- conductance activated by hyposmotic swelling was largely reversed when cell volume was reduced by applying negative pressure through the whole-cell patch pipette. CONCLUSIONS: The close relationship between the degree of cell volume increase and current activation suggests that membrane distention induced by cell swelling triggers a Cl(-)-selective conductance in cardiac myocytes.
OBJECTIVE: The aim was to apply various maneuvers to perturb the volume of cultured chick cardiac myocytes and to evaluate the association between the swelling-activated chloride conductance and membrane distention. METHODS: Swelling of single chick heart cells was induced by (1) reduction of external osmolarity; (2) elevation of intracellular osmolarity; (3) isosmotic urea uptake; and (4) positive pressure injection. Changes in cell volume and whole-cell currents were recorded simultaneously and a comparison among differently activated whole-cell currents was made in terms of time course, reversal potential (Erev), whole-cell conductance, and response to a number of channel blockers. RESULTS: Although the time course of cell swelling varied between the different experimental maneuvers, the resultant whole-cell current displayed nearly identical current-voltage relationships: outward rectification and a reversal potential near the calculated chloride equilibrium potential (ECl). The induced currents were inhibited by Cl- channel blockers, diphenylamine-2-carboxylate (DPC) and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), and were almost completely suppressed by gadolinium. In addition, the Cl- conductance activated by hyposmotic swelling was largely reversed when cell volume was reduced by applying negative pressure through the whole-cell patch pipette. CONCLUSIONS: The close relationship between the degree of cell volume increase and current activation suggests that membrane distention induced by cell swelling triggers a Cl(-)-selective conductance in cardiac myocytes.