TRPM3 is a poorly understood member of the transient receptor potential (TRP) cation channel family and endogenously expressed in pancreatic b cells. TRPM3 channels are pharmacologically activated by the neurosteroid pregnenolone sulfate (PS) and application of PS leads to an increased release of insulin from pancreatic b cells. To further investigate the role of TRPM3 in b cells we examined whether TRPM3 activity is subject to hormonal regulation. We foundthat the activity of TRPM3 channels in rat insulinoma cells (INS1) and primary mouse pancreatic b cells can be strongly inhibited by adrenaline and noradrenaline. In stark contrast, application of the muscarinic agonist carbachol was without effect on TRPM3 channel activity. With the help of various pharmacological tools like isoproterenol, prazosin, yohimbine and clonidin we determined that the adrenergic inhibition of TRPM3 is mediated by a₂-adrenoreceptors. Treatment of INS1 cells with pertussis toxin (PTX), an inhibitor of G-proteins of the i/o family, abolished the adrenergic inhibition of the TRPM3 response to PS. In line with this result, unspecific activation of heterotrimeric G-proteins with GTP-g-S strongly inhibited TRPM3 channel activity. Typically, a₂-adrenoreceptors activate Ga_i which then may inhibit adenylyl cyclases to reduce cellular cAMP levels. To test this pathway we treated INS1 or b cells with IBMX, a phosphodiesterase inhibitor, and forskolin, an activator of the adenylyl cyclase. However the inhibitory effect of noradrenaline was still prominent when intracellular cAMP levels were increased. Momentarily, we concentrate on the possible contribution of G-protein bg-subunits to the adrenergic inhibition of TRPM3 channels.