Cannabinoids activate an inwardly rectifying potassium conductance and inhibit Q-type calcium currents in AtT20 cells transfected with rat brain cannabinoid receptor

TLDR

The study stably transfected rat CB‑1 into AtT‑20 cells to examine its coupling to inwardly rectifying K⁺ currents and high‑voltage‑activated Ca²⁺ currents. Cannabinoid agonists potently activated Kir via a pertussis‑toxin‑sensitive G protein and selectively inhibited the omega‑CTX MVIIC‑sensitive Q‑type Ca²⁺ current in CB‑1–expressing AtT‑20 cells, with inhibition being voltage‑dependent and PTX‑sensitive, while anandamide produced comparable effects.

Abstract

Rat brain cannabinoid receptor (CB-1) was stably transfected into the murine tumor line AtT-20 to study its coupling to inwardly rectifying potassium currents (Kir) and high voltage-activated calcium currents (ICa). In cells expressing CB-1 (“A-2” cells), cannabinoid agonist potently and stereospecifically activated Kir via a pertussis toxin- sensitive G protein. ICa in A-2 cells was sensitive to dihydropyridines and omega CTX MVIIC, less so to omega CgTX GVIA and insensitive to omega Aga IVa. In CB-1 expressing cells, cannabinoid agonist inhibited only the omega CTX MVIIC-sensitive component of ICa. Inhibition of Q- type ICa was voltage dependent and PTX sensitive, thus similar in character to the well-studied modulation of N-type ICa. An endogenous cannabinoid, anandamide, activated Kir and inhibited ICa as efficaciously as potent cannabinoid agonist. Immunocytochemical studies with antibodies specific for class A, B, C, D, and E voltage-dependent calcium channel alpha 1 subunits revealed that AtT-20 cells express each of these major classes of alpha 1 subunit.