Verapamil-resistant contractile activation of isolated coronary artery produced by hyperosmolar solutions

Pig coronary strips were exposed to sucrose-, mannitol- or NaCl-hyperosmolar Tyrode solution and to a solution containing varying concentrations of calcium or potassium ions. In the hyperosmolar solutions obtained by addition of sucrose, mannitol and NaCl to 540, 556 and 308 mM, respectively, the resting tension was increased, while isometric tension development upon electrical stimulation was decreased. Increase in the Ca2+ and K+ concentrations augmented the phasic contraction upon electrical stimulation and produced a rise in the resting tension. The contractions produced by hyperosmolarity, high Ca2+ and K+ were susceptible to metabolic blockades, hypoxia, low temperature and glucose deprivation. The increase in the resting tension produced by hyperosmolarity was resistant to verapamil and persisted in Ca2+-free hyperosmolar solution, while the effects of additional Ca2+ and K+ on the phasic and tonic contractions were inhibited by verapamil. The results suggest that tension development in coronary artery produced by hyperosmolarity does not require verapamil-sensitive entry of Ca2+, but Ca2+ presumably supplied from intracellular stores.