Binding of __SP__ __NODE__ protein in cellular_fraction from 18 day old __SP__ atrium and 260 kd protein in cellular_fraction from 18 day old __SP__ atrium is greater than binding of __SP__ __NODE__ protein in cellular_fraction from 18 day old __SP__ heart ventricle and 260 kd protein in cellular_fraction from 18 day old __SP__ heart ventricle .