We examined the properties and regulation of Ca channels resulting from the expression of human ␣ 1B and ␣ 1E subunits stably expressed in HEK293 cells. The ancillary subunits ␤ 1B and ␣ 2 /␦ were also stably expressed in these cell lines. Ca currents in ␣ 1B -expressing cells had the properties of N-type currents. Ca currents in cells expressing ␣ 1E exhibited a novel profile that was similar to the properties of the "R type" Ca current. Introduction of GTP-␥-S into ␣ 1B cells greatly enhanced the extent of prepulse facilitation of the Ca current, whereas it had only a very small effect in ␣ 1E -expressing cells. Activation of somatostatin receptors endogenous to HEK293 cells or opioid receptors, expressed in the cells after transfection, inhibited Ca currents in ␣ 1B -expressing cells. This inhibition was blocked by pertussis toxin and was partially relieved by a depolarizing prepulse. In contrast, no inhibitory effects were noted in cells expressing ␣ 1E channels under the same circumstances. HEK293 cells normally contained G-proteins from all of the four major families. Inhibition of Ca currents by agonists in ␣ 1B -expressing cells was enhanced slightly by the cotransfection of several G-protein ␣ subunits. agonists, however, had no effect in ␣ 1E -containing cells, even after overexpression of different G-protein ␣-subunits. In summary, these results demonstrate that there is a large difference in the susceptibility of ␣ 1B -and ␣ 1E -based Ca channels to regulation by G-proteins. This is so despite the fact that the two types of Ca channels show substantial similarities in their primary sequences.