Role of CA²⁺-activated K⁺ channels in the regulation of basilar arterial tone in spontaneously hypertensive rats

1. Ionic channels appear to play an important role in contractile responses of the cerebral arteries and, thereby, contribute to the regulation of cerebral circulation. In the present study, we investigated the role of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels in the regulation of cerebral arterial tone during chronic hypertension. 2. Ring segments of the basilar artery from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were placed in bath chambers and the isometric tension of each ring was measured. 3. Application of inhibitors of BK_Ca channels, namely tetraethylammonium (TEA;≥ 0.1 mmol/L) and charybdotoxin (CTX;≥ 0.1 nmol/L), produced spontaneous contraction with rhythmic oscillation in the basilar artery from SHR. 4. The oscillatory contraction was not induced by 5-hydroxy-tryptamine (0.01-10 μmol/L) or depolarization by external high K⁺ (20-60 mmol/L). 5. The rhythmic contraction was completely abolished by either the removal of external Ca²⁺ or the application of nicardipine (10 nmol/L). 6. The oscillation was not affected by the substitution of external Cl- by various equimolar anions (i.e. acetate, benezene-sulphonate, bromide and isethianate). 7. The amplitude of the oscillation was dose-dependently increased by the vasodilators forskolin and sodium nitro-prusside, as well as by stimulation of the endothelium with histamine and acetylcholine, whereas the frequency was decreased. 8. In contrast, the oscillation was eliminated by depletion of Ca²⁺ stores by caffeine. Neither TEA (10 mmol/L) nor CTX (10 nmol/L) produced any significant contraction of the basilar artery in WKY rats. 9. These results suggest that BK_Ca channels may play an important role in regulating the resting tone of the cerebral artery in SHR.