Autoradiographic demonstration of peripheral adenosine binding sites using [3H]NECA

Autoradiographic localization of 5'-N-ethylcarboxamido[3H]adenosine ([3H]NECA) binding sites revealed a heterogeneous labeling of guinea-pig intestine with heavy labeling over the enteric ganglia and in clusters over the mucosa; a low level of label was homogeneously distributed over the muscularis externa. Under the conditions employed, no binding sites were revealed using [3H]-N6-cyclohexyladenosine ([3H]CHA), although both [3H]CHA and [3H]NECA binding sites were localized over comparable areas of rat brain. The relationship of the [3H]NECA binding sites to extracellular adenosine receptors is discussed.