Sodium tracer kinetics and transmembrane flux in tissue-cultured chick heart cells

Abstract

Considerable difficulty has been encountered in defining the physiological significance of sodium tracer kinetic measurements in cardiac muscle. In this study, 24Na+ efflux experiments were performed by directly monitoring tissue radioactivity during the superfusion of growth-oriented embryonic chick heart cells in tissue cultured. The cellular 24Na+ efflux from contractile preparations exhibited at least two exponential components whereas noncontractile, fibroblastlike preparations had a single efflux component similar in rate to the slower component of the contractile preparations. We concluded that the slow component represents efflux from nonmuscle cells, whereas the faster component reflects the muscle cell compartment. The mean Na+ efflux rate constants for contractile preparations (beating 150 min-1) were 3.1 and 0.35 min-1. Intracellular Na+ concentrations, as determined by isotope uptake and by flame photometry, were 18 and 16 mM for contractile and nonmuscle preparations, respectively. The steady-state, transmembrane fluxes are 98 and 5 pmol . cm-2 . s-1 for muscle and nonmuscle cells, respectively. The Na+ efflux kinetics in 10(-4) M ouabain were reduced by approximately 16% from the control value. These findings indicate that the greater part of the steady-state Na+ efflux in cultured heart cells is due to mechanisms other than the Na+-K+ pump.

Kinetics of thallium exchange in cultured rat myocardial cells.

“…Several explanations could account for the difference, (1) the present experiments were carried out at 37°C compared to 21-23°C for the others (2) much lower concentrations of Tl + were used in the present studies (3) the preparation, having a single, rapidly exchangeable extracellular compartment, allows accurate flux determinations without contamination from trapped inhibitors such as K + , and, finally, (4) the active transport properties of the preparation itself could be unique. The last factor is least likely since it has been shown (McCall, 1979;Wheeler et al, 1982) that cation transport by cultured myocardial cells is similar to that in other myocardial preparations. This is further supported by the observation in this study that the K m of K + on the active K + influx is 1.8 irtM, identical to that for both Na pump activity and ATPase activity (Glynn, 1968;Glitsch et al, 1978, Gadsby, 1980 in a wide variety of tissues.…”

“…The preparation used was chosen because of the presence of a single, rapidly exchangeable, extracellular compartment, which greatly facilitates flux determination, and because many of the cell's membranexharacteristics (McCall, 1979;Wheeler et al, 1982) are similar to those of other myocardial preparations.…”

Sodium/calcium exchange in mammalian ventricular muscle: a study with sodium‐sensitive micro‐electrodes.

“…for frog ventricle (Keenan & Niedergerke, 1967). In growth-orientated embryonic chick Wheeler, Horres & Lieberman (1982) find a Na efflux of 98 pmol/cm2 . s but only around 16 pmol/cm2 .…”

Refined Evaluation of the Exponential Curve Parameters and Initial Exchange Rate Constant for 22Na+ Washout in Cultured Human Skin Fibroblasts

“…A value of 0.42 min-' was documented for 22Na+ exchange rate constant of cultured chick heart nonmuscle cells primarily consisting of fibroblasts (6). In cultured rat fibroblasts, a 22Na+ efflux rate constant of 0.32 m i d was found (28).…”