Transepithelial transport in cell culture: Bioenergetics of Na‐, D‐glucose‐coupled transport

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Abstract
The renal cell line LLC‐PK1 contransports Na and D‐glucose from the apical to the basolateral side of the cell monolayer, and the short‐circuit current (Isc) measures the net amount of Na transported. Under conditions of maximal cotransport, the addition of phlorizin or removal of Na rreversibly decreased oxygen consumption by one‐hal. In the absence of glycolytic substrates, α‐methyl‐D‐glucoside stimulated Isc and oxygen consumption, although the Isc came to a steady state 50% less than when glycolytic substrates were present. The addition of other aerobic substrates did not increase Isc; however, when non‐contransported glycolytic substrates were introduced the Isc returned to a maximum with an associated fall in oxygen consumption and increased lactate production. Thus, in the absence of glycolytic substrates aerobic ATP formation may be rate‐limiting for Na, D‐glucose contansport. For this epithelium glycolysis makes an impotant contribution to the provision of energy or transport. Oxygen consumption does not correlate well with Isc and is not a good measured off the energy used in transport.