Maintenance of fast Na-channels during primary culture of embryonic chick heart cells

Abstract

Cells isolated from 6-day-old chick embryonic heart were cultured for periods up to 5 days. Their electrical activity was recorded and resting membrane potential or maximal diastolic potential, threshold potential and maximal upstroke velocity were analyzed after 4, 24 and 48 h and 4 or 5 days of culture. The spontaneously beating cells have a low maximal diastolic potential at 4 and 24 h after the dissociation treatment. Spontaneous activity may be supported by fast Na-channels and/or by slow channels. After 48 h of culture, very few cells remain spontaneously active. The resting membrane potential and maximal upstroke velocity of quiescent cells recover values close to that of the cells in vivo. Later, myocardial cells are gathered in mono or multilayers with many fibroblasts. Although their maximal diastolic potential remains highly negative they contract spontaneously. These cells have a low maximal upstroke velocity and show no or very little tetrodotoxin sensitivity. When a spontaneously active cell is stimulated at a higher rate, the rate and the amplitude of the diastolic depolarization decrease while the maximal upstroke velocity increases. In “pure culture”, myocardial cells form isolated clumps which are generally quiescent and which, when stimulated, develop fast rising, tetrodotoxin-sensitive action potentials. Appearance of automaticity, low maximal upstroke velocity and tetrodotoxin insensitivity have been proposed as criteria for “dedifferentiation” of cultured myoblasts. It is suggested, here, that these changes result from the dissociation process and later from the proliferation of fibroblasts and that the membrane of myocardial cells keeps its excitability properties unchanged.