Similar localisation of alpha(1)- and beta-adrenoceptors in rabbit heart in relation to sympathetic nerve endings

Electrically driven (1 Hz) rabbit papillary muscles were examined ex vivo f or the localisation of the alpha(1)- and beta-adrenoceptor populations rela tive to the sympathetic nerve endings and to each other. We determined the influence of neuronal uptake blockade by cocaine upon the horizontal positi on of the dose-response curves for the inotropic and lusitropic effects exe rted by noradrenaline in the presence of extra neuronal uptake blockade by hydrocortisone and in the presence and absence of adrenoceptor blockers. Co caine similarly shifted the dose-response curves for both alpha(1)- and bet a-adrenoceptors mediated effects to 10-30 times lower concentrations of nor adrenaline. This potentiation by cocaine indicates that also the alpha(1)-a drenoceptor population is located close to or within the sympathetic synapt ic clefts, as is known for the beta-adrenoceptor population. (C) 1999 Elsev ier Science B.V. All rights reserved.