Mechanisms by which BKCa(large-conductance calcium-sensitive potassium) channels are involved in vascular remodeling in hypertension are not fully understood. Vascular smooth muscle cell (VSMC) proliferation and vascular morphology were compared between hypertensive and normotensive rats. BKCachannel activity, protein expression, and interaction with IP3R (inositol 1,4,5-trisphosphate receptor) were examined using patch clamp, Western blot analysis, and coimmunoprecipitation. On inside-out patches of VSMCs, the Ca2+-sensitivity and voltage-dependence of BKCachannels were similar between hypertensive and normotensive rats. In whole-cell patch clamp configuration, treatment of cells with the IP3R agonist, Adenophostin A (AdA), significantly increased BKCachannel currents in VSMCs of both strains of rats, suggesting IP3R-BKCacoupling; however, the AdA-induced increases in BKCacurrents were attenuated in VSMCs of hypertensive rats, indicating possible IP3R-BKCadecoupling, causing BKCadysfunction. Co-immunoprecipitation and Western blot analysis demonstrated that BKCaand IP3R proteins were associated together in VSMCs; however, the association of BKCaand IP3R proteins was dramatically reduced in VSMCs of hypertensive rats. Genetic disruption of IP3R-BKCacoupling using junctophilin-2 shRNA dramatically augmented Ang II-induced proliferation in VSMCs of normotensive rats. Subcutaneous infusion of NS1619, a BKCaopener, to reverse BKCadysfunction caused by IP3R-BKCadecoupling significantly attenuated vascular hypertrophy in hypertensive rats. In summary, the data from this study demonstrate that loss of IP3R-BKCacoupling in VSMCs induces BKCachannel dysfunction, enhances VSMC proliferation, and thus, may contribute to vascular hypertrophy in hypertension.