5-Hydroxytryptamine₁-like receptors linked to increases in intracellular calcium concentration and inhibition of cyclic AMP accumulation in cultured vascular smooth muscle cells derived from bovine basilar artery

Vascular smooth muscle cells derived from bovine basilar artery by the explant method were grown in culture. In the presence of 1 μM forskolin and the phosphodiesterase inhibitor rolipram, 5-hydroxytryptamine (5-HT) agonists inhibited by 90 to 100% the accumulation of intracellular cyclic AMP (cAMP) with a rank order of potency 5-carboxamidotryptamine (5-CT) ≥ 5-HT > 5- benzyloxytryptamine = sumatriptan > RU24969 [5-methoxy-3(1,2,3,6-tetrahydro- 4-pyridinyl)-1H indole succinate] > (±)-8-hydroxydipropylaminotetralin. In suspensions of cells loaded with the calcium-sensitive probe fura-2, 5-CT and 5-HT caused a biphasic increase in the concentration of intracellular free calcium ([Ca⁺⁺](i)) that consisted of both transient and sustained phases. The transient phase was reduced and the sustained phase abolished in the absence of extracellular calcium. The EC₅₀ for 5-CT-induced increase in [Ca⁺⁺](i) (6 nM) was similar to that for inhibition of cAMP accumulation (1.3 nM). Both the inhibition of cAMP accumulation and increase in [Ca⁺⁺](i) were inhibited by the antagonist methiothepin (pA₂ = 8.9), but not by the antagonists ketanserin, spiperone and pindolol. Both the inhibition of cAMP accumulation and increase in [Ca⁺⁺](i) were attenuated by greater than 85% in cells that were pretreated with pertussis toxin. PI turnover was not stimulated by 5-CT. The rank order of agonist potency, as well as the antagonist sensitivity, indicates responses mediated by one or more 5-HT₁-like-type receptors. Bovine basilar artery cells that naturally express 5-HT₁-like receptors may serve as a useful model for the study of 5- HT₁-like receptor-mediated signal transduction mechanisms in vascular smooth muscle.