Ghrelin signalling in guinea-pig femoral artery smooth muscle cells

Aim: Our aim was to study the new signalling pathway of ghrelin in the guinea‐pig femoral artery using the outward I_K as a sensor. Methods: Whole‐cell patch‐clamp experiments were performed on single smooth muscle cells, freshly isolated from the guinea‐pig femoral artery. The contractile force of isometric preparations of the same artery was measured using a wire‐myograph. Results: In a Ca²⁺‐ and nicardipine‐containing external solution, 1 mmol L^?1 tetraethylammonium reduced the net I_K by 49 ± 7%. This effect was similar and not additive to the effect of the specific BK_Ca channel inhibitor iberiotoxin. Ghrelin (10^?7 mol L^?1) quickly and significantly reduced the amplitudes of tetraethylammonium‐ and iberiotoxin‐sensitive currents through BK_Ca channels. The application of 5 × 10^?6 mol L^?1 desacyl ghrelin did not affect the amplitude of the control I_K but it successfully prevented the ghrelin‐induced I_K decrease. The effect of ghrelin on I_K was insensitive to selective inhibitors of cAMP‐dependent protein kinase, soluble guanylyl cyclase, cGMP‐dependent protein kinase or a calmodulin antagonist, but was effectively antagonized by blockers of BK_Ca channels, phosphatidylinositol‐phospholipase C, phosphatidylcholine‐phospholipase C, protein kinase C, SERCA, IP₃‐induced Ca²⁺ release and by pertussis toxin. The ghrelin‐induced increase in the force of contractions was blocked when iberiotoxin (10^?7 mol L^?1) was present in the bath solution. Conclusions: Ghrelin reduces I_K(Ca) in femoral artery myocytes by a mechanism that requires activation of Gα_i/o‐proteins, phosphatidylinositol phospholipase C, phosphatidylcholine phospholipase C, protein kinase C and IP₃‐induced Ca²⁺ release.