The aim of this study was to determine the expression of the endothelin receptor subtype mRNAs in human detrusor cultured smooth muscle cells using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization (ISH), First strand cDNA was made from human detrusor cultured smooth muscle cells total RNA and used for PCR with primers designed to amplify fragments of the ETA and ETB endothelin receptor subtype cDNA sequences. Subcloned fragments of the ETA and ETB endothelin receptor cDNAs were used to synthesize digoxigenin-labeled cRNA probes by in vitro transcription, COS-7 cells transfected with the ETA and ETB receptor cDNAs were used as positive control and to confirm the absence of cross-hybridization due to sequence homology, Both ETA and ETB receptor mRNAs were detected by RT-PCR analysis. By ISH, both ETA and ETB receptor subtype mRNAs were detected. However, ETA signal was much more intense than ETB signal. These results indicate that mRNAs for both ETA and ETB receptors are expressed in detrusor smooth muscle cells of human urinary bladder. The ETA receptor is the predominant detrusor ET receptor. Copyright (C) 2000 S. Karger AG, Basel.