title: Influence of changes in external potassium and chloride ions on membrane potential and intracellular potassium ion activity in rabbit ventricular muscle.
abstract: 1. The membrane responses of rabbit papillary muscles to rapid changes in [K](o) and [Cl](o) were measured with open-tipped micropipettes and with closed micropipettes made from K-selective glass.2. The muscle cells behaved primarily as a K electrode, and responses to changes in [K](o) with constant [Cl](o) or with constant [K](o) x [Cl](o) were substantially the same.3. When [Cl](o) was changed at a constant [K](o) the membrane potentials changed rapidly and symmetrically by a small value and remained constant for 30 min.4. Measurement of potential with K(+)-selective micro-electrodes in these experiments showed no change in intracellular K activity. In addition to permitting calculation of K permeability, these measurements reassured us that the K(+)-selective electrodes were well insulated and not influenced by electrical shunts at the impalement site.5. Although the membrane response to changes in [Cl](o) was small, it was possible to calculate that the permeability ratio (P(Cl)/P(K)), was 0.11. The Cl and K conductances were about 0.015 mmho/cm(2) and 0.09 mmho/cm(2) respectively, resulting in a conductance ratio (g(Cl)/g(K)) of about 0.17.6. The time course of depolarization by increase in [K](o) was rapid (half-time 5 sec), but repolarization on return to lower [K](o) was much slower (half-time 50 sec). The depolarization time course was easily fitted by the potential change calculated by assuming the need for K diffusion into the extracellular spaces and taking account of the logarithmic relation between membrane potential and [K](o). These calculations did not fit the time course of repolarization, which was slowed in the fashion expected from an inward-rectifying membrane.7. The influence of [K](i) on membrane potential was investigated by changes in tonicity of the external solution. Hypotonic solution produced a change in intracellular K activity close to that produced by ideal water movement. However, in hypertonic solution, intracellular K activity did not rise as much as predicted, suggesting a change in intracellular activity coefficient.
mesh_terms: D000818:Animals; D002712:Chlorides / Q000494:pharmacology*; D004058:Diffusion; D004553:Electric Conductivity; D007424:Intracellular Fluid / Q000032:analysis; D008564:Membrane Potentials / Q000187:drug effects*; D008839:Microelectrodes; D009132:Muscles / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism; D010539:Permeability; D011188:Potassium / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D011817:Rabbits
chemical_list: D002712:Chlorides; D011188:Potassium