Abstract

We constructed Chinese hamster ovary (CHO) cells stably expressing α_1A-, α_1B-, or α_1D-adrenergic receptors (CHO-α_1A, CHO-α_1B, or CHO-α_1D, respectively) and compared the Ca²⁺channels activated by noradrenaline (NA) in these cells using whole-cell recordings and monitoring of the intracellular free Ca²⁺ concentration ([Ca²⁺]_i). We also investigated the involvement of Ca²⁺ channels in the NA-induced arachidonic acid release. In all three cell types, NA at concentrations ≥10 nM induced a sustained increase in [Ca²⁺]_i attributable to extracellular Ca²⁺ influx in [Ca²⁺]_i monitoring and an inward current in whole-cell recording. The current-voltage relationships were linear, and their reversal potentials were close to 0 mV. The reversal potential of the currents was not affected by a change in the concentration of Cl⁻ in the bath solution. Moreover, a current could be induced in a bath solution containing only Ca²⁺ as the movable cation. LOE 908, a receptor-operated Ca²⁺ channel blocker, inhibited the sustained increase in [Ca²⁺]_i and inward currents in a concentration-dependent manner, and complete inhibition was observed at concentrations ≥ 3 μM. NA induced arachidonic acid release in all three cell types. This release was entirely dependent on extracellular Ca²⁺ influx. Moreover, LOE 908 at concentrations ≥ 3 μM blocked the NA-induced increase in arachidonic acid release. These results indicate that 1) NA activates LOE 908-sensitive Ca²⁺-permeable nonselective cation channels (NSCCs) in CHO-α_1A, CHO-α_1B, and CHO-α_1D, and 2) the Ca²⁺ influx through NSCCs may play an important role in the NA-induced enhancement of arachidonic acid release in these cells.