Intracellular potassium and sodium activities of chick ventricular muscle during embryonic development.

Abstract

1. The basis of the resting potential of chick embryo ventricular muscle was studied by use of ion‐selective micro‐electrodes. Membrane resting potential hyperpolarized from ‐65 . 4 +/‐ 1 . 1 mV (mean +/‐ S.E.) at age 4 day to ‐75 . 8 +/‐ 0 . 6 mV at age 18 day. Action potential overshoot increased from +19 . 8 +/‐ 0 . 9 at age 4 day to +33 . 1 +/‐ 0 . 6 mV at age 18 day. 2. Intracellular K+ activity measured with ion‐selective micro‐electrodes increased from 71 . 3 +/‐ 1 . 9 mM at age 4 day to 89 . 9 +/‐ 1 . 1 at age 18 day. Intracellular Na+ activity decreased from 12 . 5 +/‐ 0 . 4 to 7 . 0 +/‐ 0 . 3 mM during the same period. The difference between membrane resting potential and the calculated potassium equilibrium potential decreased with development. PNa/PK estimated from the constant field equation decreased from 0 . 012 at age 4 day to 0 . 005 at age 18 day. 3. The hyperpolarization of resting potential and the increased action potential overshoot during development could be explained by a rise in intracellular K+ activity and a fall in intracellular Na+ activity, as if the Na‐‐K exchange pump became more active. © 1980 The Physiological Society