Physiologic criteria for electrogenic transport in tissue-cultured heart cells.

A description of the physiologic criteria for electrogenic transport in cultured heart cells must consider the direct as well as the indirect contributions of the electrodiffusive and electroneutral transport mechanisms of the kind described in this chapter. It is important to recognize that fundamental transport processes whether active, passive, or coupled-passive, do not operate in isolation but function rather as an interrelated network represented by the example in Fig. 8. The results of our studies point to the importance of providing an accurate, quantitative description of the transmembrane movement of sodium, because this ion is intricately involved in the overall regulation of several transport mechanisms in cardiac muscle. Cultured heart cell preparations enable the rapid exchange of extracellular space essential to the study of complex transport mechanisms. These preparations have thus enhanced our understanding of the magnitude and interplay of exchange fluxes that may eventually be implicated in the repolarization phase of the cardiac action potential and genesis of pacemaker potentials.