AJP - Heart and Circulatory Physiology, Vol 248, Issue 5 622-H630, Copyright © 1985 by American Physiological Society
Passive membrane properties of isolated feline ventricular myocytes
S. R. Houser, A. Bahinski and L. H. Silver
Membrane properties of adult mammalian cardiac muscle are difficult to
define mainly because of experimental complications arising from complex
packing of myocytes in the tissue matrix. Isolated feline myocytes were
used in the present study to avoid these complications. The objectives of
this study were to define the functional relationship between passive
unidirectional transmembrane potassium (K+) fluxes, membrane permeability
to K+ (PK), and membrane K+ (Ko) dependency of this relationship. Passive
(ouabain-insensitive) components of unidirectional K+ fluxes were measured
with 42K, and membrane potential (Em) and membrane (slope) conductance (gm)
were measured with electrophysiological techniques. Myocytes studied in
solutions with 5 mM K+o had normal resting potentials (-81 +/- 1 mV). The
input resistance and membrane time constant were 2.72 +/- 0.47 X 10(-7)
omega and 7.01 +/- 1.0 ms, respectively. When K+o was lowered Em
hyperpolarized, input resistance (Ri) increased, and K+ fluxes decreased.
When K+o was increased Em depolarized, Ri decreased, and K+ fluxes
increased. These data were combined to determine whether K+ fluxes obey the
independence principle and to calculate PK and gK. The results obtained
support the idea that 1) unidirectional K+ fluxes do not obey the
independence principle, 2) PK is much greater than the membrane
permeability to other ions, and 3) the gK calculated from passive K+ fluxes
was similar to the gm measured electrically (at all K+o's tested).
