Alterations of bile acid and bumetanide uptake during culturing of rat hepatocytes

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Abstract
Uptake by the multispecific bile acid transport system of [3H]taurocholate, [14C]cholate, and [3H]-bumetanide into primary cultures of rat hepatocytes was compared with their uptake into freshly isolated rat hepatocytes. The uptake maximum velocity (Vmax) of all compounds declined in primary culture, whereas the Michaelis constant (Km) values remained stable. Loss of uptake was not due to the reduction of driving forces as evaluated from the level of ATP and the activity of Na(+)-K(+)-ATPase. No alpha-fetoprotein was detectable in culture supernatants. Neither growth factors (glycylhistidyl-lysine, epidermal growth factor), peroxisome and cell proliferators (nafenopin, dimethyl sulfoxide), nor bile acids prevented the loss of transport in hepatocyte culture. However, addition of dibutyryl adenosine 3'5'-cyclic monophosphate protracted the transport activity significantly. When cultured rat hepatocytes with reduced transport were detached by trypsin, cells rounded up and showed the same uptake capacity for bumetanide, cholate, and taurocholate as seen in freshly isolated hepatocytes. "Cryptic" transport activity in the lower basolateral membrane facing the support was found using an incubation chamber for cultured hepatocytes, which allowed us to distinguish simultaneously between uptake via the upper and lower basolateral membrane of the cultured cells.