Intracellular chloride activity in rabbit papillary muscle: effect of serum

The intracellular chloride activity (aiCl), measured with Cl-selective microelectrodes on stimulated rabbit papillary muscles (1 Hz) incubated in serum, was 7.2 +/- 2.2 mM (48 measurements). Under the same condition, on the quiescent muscle, aiCl was 7.5 +/- 2.8 mM (45 measurements). The membrane potential of quiescent papillary muscles and diastolic potential of stimulated papillary muscles were -79.0 +/- 0.7 (50 measurements) and -83.5 +/- 0.5 mV (50 measurements), respectively. The experimental conditions were chosen to reproduce the in vivo conditions where the Cl equilibrium potential is close to the membrane potential or to the diastolic potential. After correcting for cytoplasmic interference (4 mM) on the aiCl measurements, the Cl equilibrium potential (ECl) was -84 mV. In conclusion, the Cl distribution in cardiac cells bathed in serum is passive as for in vivo cardiac cells.