Alpha-adrenergic receptors regulate human lymphocyte amiloride-sensitive sodium channels

Two independent signal transduction pathways regulate lymphocyte amiloride-sensitive sodium channels (ASSCs), one utilizing cAMP as a second messenger and the other utilizing a GTP-binding protein. This implies that two plasma membrane receptors play a role in the regulation of lymphocyte ASSCs. In this study, we tested the hypothesis that alpha1- and alpha2-adrenergic receptors independently regulate lymphocyte ASSCs via the two previously identified second messengers. Direct measurements indicated that norepinephrine increased lymphocyte cAMP and activated ASSCs. The alpha2-specific inhibitor, yohimbine, blocked this activation, thereby linking alpha2-adrenergic receptors to ASSC regulation via cAMP. The alpha1-specific ligand, terazosin, acted as an agonist and activated lymphocyte ASSCs but inhibited ASSC current that had been preactivated by norepinephrine or 8-(4-chlorophenylthio) (CPT)-cAMP. Terazosin had no effect on the lymphocyte whole cell ASSC currents preactivated by treatment with pertussis toxin. This finding indirectly links alpha1-adrenergic receptors to lymphocyte ASSC regulation via GTP-binding proteins. Terazosin had no direct inhibitory or stimulatory effects on alpha,beta,gamma-endothelial sodium channels reconstituted into planar lipid bilayers and expressed in Xenopus oocytes, ruling out a direct interaction between terazosin and the channels. These findings support the hypothesis that both alpha1- and alpha2-adrenergic receptors independently regulate lymphocyte ASSCs via GTP-binding proteins and cAMP, respectively.