The changes in CiNa of sheep cardiac Purkinje fibres in hyperosmotic solutions.

1. The changes in intracellular sodium ion concentration (CiNa) of sheep cardiac Purkinje fibres in hyperosmotic solutions were studied using Na-sensitive liquid ion-exchanger microelectrodes. 2. CiNa was increased in hyperosmotic solutions containing different concentrations of sucrose from 0 to 300 mM. 3. The changes in resting membrane potential (RMP) in hyperosmotic solutions had no regularity. In most of the experiments there was hyperpolarization of the membrane but in a few cases a depolarization or no change of RMP were also observed. 4. The N-shape of I-V relations of the fibres became more pronounced in hyperosomotic solutions.