Heterogenic contractile response of rat left ventricular myocytes to β1-adrenoceptor stimulation

We measured the contractile response of left ventricular cardiac myocytes from female rats to selective β1-adrenoceptor stimulation (isoprenaline, 10−8 M and 10−7 M in the presence of 10−7 M ICI 118,551 a β2-adrenoceptor inverse agonist). A heterogenic response to stimulation, inversely related to the extent of cell shortening prior to adrenergic stimulation, was observed. Challenge of cardiac myocytes with a selective β1-antagonist, atenolol (10−7 M), suggests the heterogenic response is not caused by basal β1-adrenoceptor activity. Thus, basal myocyte contractility determines the response to β1-adrenoceptor stimulation, this should be taken into account when experimental conditions are designed.