RAPID EXPRESSION OF THE NA-CA-2+ EXCHANGER IN RESPONSE TO CARDIAC PRESSURE-OVERLOAD()

This report identifies a rapid increase in the expression of cardiac N a+-Ca2+ exchanger mRNA in response to an acute pressure overload. This enhanced exchanger expression appeared within 1 h after the onset of right ventricular pressure overload in the cat and was sustained durin g cardiac overloading for at least 4 h. Maintenance of this right vent ricular pressure overload for 48 h evoked an increase in the productio n of exchanger protein. Because of our previous finding that load impo sition on the heart initiates cell growth and our hypothesis that this is in response to the enhanced entry of cellular cations, we then exa mined the effect of Na+ influx into cultured adult cardiac myocytes, o r cardiocytes, in terms of early anabolic responses. Pressure overload of the heart and cardiocyte Na+ influx were found to produce a common , rapid result in terms of both enhanced Na+-Ca2+ exchanger expression and accelerated synthesis of general and contractile proteins, the ha llmarks of cardiac hypertrophy.