COMPARISON OF THE GATING BEHAVIOR OF HUMAN AND MURINE CYSTIC-FIBROSISTRANSMEMBRANE CONDUCTANCE REGULATOR CL- CHANNELS EXPRESSED IN MAMMALIAN-CELLS

1. To in investigate the function of the murine cystic fibrosis transm embrane conductance regulator (CFTR), a full-length cDNA encoding wild -type murine CFTR ras assembled and stably expressed in Chinese hamste r ovary (CHO) cells. 2. Like human CPTR, murine CFTR formed Cl- channe ls that were regulated by cAMP-dependent phosphorylation and intracell ular ATP. However, murine CFTR Cl- channels had a reduced single-chann el conductance and decreased open probability (P-o) compared with thos e of human CFTR. 3. analysis of the dwell time distributions of single channels suggested that the reduced P-o of murine CFTR was caused by both decreased residence in the open state and transitions to a new cl osed state, described by an intermediate closed time constant. 4. For both human and murine CFTR, ATP and ADP regulated the rate of exit fro m the long-lived closed state. 5. 5'-Adenylylimododiphosphate (AMP-PNP ) and pyrophosphate, two compounds that disrupt cycles of ATP hydrolys is, stabilized the open state of human CFTR. However, neither agent lo cked murine CFTR Cl- channels open, although AMP-PNP increased the P-o of murine CFTR. 6. The data indicate that although human and murine C FTR have many properties in common, some important differences in func tion are observed. These differences could be exploited in future stud ies to provide new understanding about CFTR.