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 h eart by radioligand binding assays. We also determined the role of this sub type in stimulating phosphoinositide (PI) hydrolysis in adult rat cardiac m yocytes. BMY 7378 inhibited [H-3]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-induce d 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 conce ntrations up to 100 nM, did not significantly affect the concentration-resp onse 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. (C) 2001 Academic Press.