Lymphocyte membrane adenosine receptors coupled to adenylate cyclase: properties and occurrence in various lymphocyte...

Lymphocytes possess membrane adenosine receptors through which this nucleoside or analogs activate adenylate cyclase. Several adenosine analogs - 5'-N-ethylcarboxamide adenosine (NECA), N6-(L-2-phenyl-isopropyl) adenosine (PIA), 2-chloro adenosine (Cl-Ado) - were tested on the adenylate cyclase of mouse thymocyte homogenates; the order of potencies: NECA greater than Cl-Ado greater than PIA is consistent with the order which has been assumed to be characteristic of Ra type adenosine receptors. The stimulation of thymocyte adenylate cyclase by NECA was biphasic while the responses to Cl-Ado and PIA were not, which suggests the existence of Ra sub-types of adenosine receptors. Moreover, these adenosine receptors were found to be present in several lymphocyte subclasses: mature and immature mouse thymocytes, B and T mouse splenocytes, human peripheral blood lymphocytes, and also in lymphoblastoid cell lines. No crucial differences were observed between the adenylate cyclase stimulations of the various population by NECA.