Toward an understanding of the complete NCX1 lifetime in the cardiac sarcolemma.

The density of Na/Ca exchangers (NCX1) in the cardiac sarcolemma, like all plasma membrane proteins, will be influenced by (and ultimately determined by) the function of membrane insertion and retrieval processes (i.e., exo- and endocytic mechanisms). Progress in understanding these processes in cardiac muscle faces many biological and methodological complexities and hurdles. As described here, we are attempting to overcome these hurdles to study more adequately the assembly and disassembly of the cardiac sarcolemma, in general, and the control of NCX1 by membrane trafficking processes in particular. First, we have developed improved noninvasive methods to monitor the cellular capacitance of cardiac tissue (NIC) over periods of hours. Thus, we can study long-term changes of total membrane area. Second, we have developed mice that express fusion proteins of NCX1 with the pHluorin green protein. Thus, we can determine the membrane disposition of NCX1, and changes thereof, on-line in intact cardiac muscle.