Hepatocytes from α1B‐adrenoceptor knockout mice reveal compensatory adrenoceptor subtype substitution

• Published in: British journal of pharmacology 2004-07, Vol.142 (6), p.1031-1037
• Main Authors: Deighan, Clare, Woollhead, Alison M, Colston, Janet F, McGrath, John C
• Format: Article
• Language: English
• Subjects: Confocal laser‐scanning microscopy; hepatocyte and adrenergic; QAPB; radioligand binding
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0705872

α1‐Adrenoceptors (ARs) play an important functional role in the liver; yet little is known about their cellular location. We identified the subtypes present in wild‐type (WT) and α1B‐AR knockout (KO) mice livers at 3 and 4 months of age, and investigated their distribution in hepatocytes. The fluorescent α1‐AR antagonist quinazolinyl piperazine borate‐dipyrromethene (QAPB) was used to visualise hepatic α1‐ARs and radioligand binding with [3H]‐prazosin was used to quantify the α1‐AR population. QAPB and [3H]‐prazosin bound specifically to hepatic α1‐ARs with nanomolar affinity. The cellular distribution of α1‐ARs was similar in WT and α1B‐AR KO hepatocytes; QAPB binding was distributed diffusely throughout the cell with no binding evident on the plasma membrane. Radioligand binding produced Bmax values as follows: 3‐month WT – 76±3.3 fmol mg−1; 4‐month WT – 50±3.1 fmol mg−1; 3‐month α1B‐AR KO – 7.4±0.73 fmol mg−1; 4‐month α1B‐AR KO – 30±2.0 fmol mg−1. In 3‐ and 4‐month WT liver, all antagonists acted competitively. RS100329 (α1A‐selective) and BMY7378 (α1D‐selective) bound with low affinities, indicating the presence of α1B‐ARs. In 4‐month α1B‐AR KO liver prazosin produced a biphasic curve, whereas RS100329 and BMY7378 produced monophasic curves of high and low affinity, respectively, indicating the presence of α1A‐ARs. In conclusion, we have made the novel observation that α1‐ARs can compensate for one another in the absence of the endogenously expressed receptor; yet there appears to be no subtype‐specific subcellular location of α1‐ARs; the WT livers express α1B‐ARs, while α1B‐AR KO livers express α1A‐ARs. This study provides new insights into both hepatocyte and α1‐AR biology. British Journal of Pharmacology (2004) 142, 1031–1037. doi:10.1038/sj.bjp.0705872