alpha(1D)-Adrenoceptors do not contribute to phosphoinositide hydrolysis in adult rat cardiac myocytes.

We have used the alpha(1D)-adrenoceptor selective antagonist, BMY 7378, to investigate the presence of alpha(1D)-adrenoceptor subtype in adult rat heart by radioligand binding assays. We also determined the role of this subtype in stimulating phosphoinositide (PI) hydrolysis in adult rat cardiac myocytes. BMY 7378 inhibited [(3)H]prazosin binding to cardiac membranes in a biphasic mode with a pK(i) of 9.19 +/- 0.26 for high affinity sites and 6.64 +/- 0.09 for low affinity sites. The inhibition of the adrenaline-induced stimulation of PI hydrolysis by BMY 7378 fitted a one-site model and the calculated pK(b) value (6.92 +/- 0.28) was consistent with the involvement of alpha(1A) and alpha(1B) adrenoceptors. In addition, BMY 7378, at concentrations up to 100 nM, did not significantly affect the concentration-response curves for the adrenaline-induced stimulation of PI hydrolysis. Taken together, these data suggest that alpha(1D)-adrenoceptors are expressed in adult rat heart but this subtype is not involved in the adrenaline-induced stimulation of PI hydrolysis.