Intracellular Potassium Activity in Guinea Pig Papillary Muscle during Prolonged Hypoxia

Thomas Guarnieri; Harold C. Strauss

doi:10.1172/JCI110467

Intracellular Potassium Activity in Guinea Pig Papillary Muscle during Prolonged Hypoxia

Thomas Guarnieri and Harold C. Strauss

Published February 1, 1982 - More info

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Abstract

During prolonged hypoxia, intracellular potassium concentration, [K]_i has been reported to fall by 70% with a concomitant decrease in the calculated potassium equilibrium potential, E_K. Nevertheless, resting membrane potential, V_m, declined only slightly. Because V_m depolarized very little in relation to the calculated E_K, it was hypothesized that electrogenic Na-K pumping contributed up to 40 mV to V_m during prolonged hypoxia. To further test this hypothesis we studied what changes prolonged hypoxia makes in the thermodynamically active fraction of cellular potassium, intracellular potassium activity, α_Kⁱ, and how change in α_Kⁱ affects the relationship between V_m, E_K and, by inference, the Na-K pump. Using double-barrel K-selective electrodes, V_m and α_Kⁱ were measured in quiescent guinea pig right ventricular papillary muscles superfused for 8 h with hypoxic Tyrode's solution. Over the 8-h period both V_m and α_Kⁱ decreased. However, the decline in V_m was paralleled by a decrease in the E_K calculated from α_Kⁱ. At no time was there hyperpolarization of V_m beyond E_K.

After 8 h the Na-K pump was inhibited by exposing the muscles to 0.1 mM ouabain. The onset of an increase in extracellular potassium activity, measured with a double-barrel electrode, was used to mark the amount of depolarization of V_m due solely to pump inhibition. After hypoxia, V_m depolarized 8.4±4.4 mV before extracellular potassium activity (α_K^e) increased. Thus, the decrease in α_Kⁱ during hypoxia is much less than that reported for [K]_i. The parallel decline in V_m and E_K and the small depolarization of V_m with ouabain suggest that after prolonged hypoxia the Na-K pump continues to contribute to V_m, but the amount of this contribution is substantially less than previously reported.