Rocking promotes differentiated properties in LLC-PK cells by improved oxygenation

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Abstract
Previous studies from our laboratory indicated that in contrast to cells cultured under still conditions, LLC-PK cells cultured under conditions of continuous rocking exhibit pH-modulated ammonia production and also manifest lower levels of lactate dehydrogenase activity. In the present studies, we assessed whether other metabolic features and parameters of differentiation are modified by rocking. Rocked, as contrasted with still, cultures exhibited decreased medium lactate production and increased cellular ATP content consistent with heightened oxidative metabolism. Still cultures did not exhibit either dome formation or sodium-dependent alpha-methylglucoside uptake until the cultures reached full confluency. By contrast, rocked cultures underwent dome formation as well as enhanced alpha-methylglucoside uptake during the growth phase, and these parameters were quantitatively greater than in still culture even after full confluency was achieved. Thus rocking promotes several functions, which can reflect differentiation in LLC-PK cells. To determine whether provision of adequate oxygen accounts for the enhancement of cellular metabolism and differentiated functions by rocking, still cultures grown in a high oxygen concentration of 36% were compared with standard cultures grown in 18% oxygen. The high oxygen environment resulted in the development of pH-modulated ammonia production, a decrease in lactate dehydrogenase activity, lower medium lactate formation, increased ATP levels, more copious dome formation, and increased alpha-methylglucoside uptake. Thus rocking promotes cellular metabolism and differentiated functions by the provision of adequate oxygenation.