Concentration-related differences in the effects of the Ca2+ agonist Bay K 8644 in human bronchus in vitro.

Abstract 1. 1. In human isolated bronchial muscle Bay K 8644 (1 nM-1 μM) increased the force of contraction. In concentrations greater than 1 μM (in sensitized tissues), and 10 μM (in control), Bay K 8644 relaxed tissues to below their pretreatment baseline tension. 2. 2. In control tissues contracted with methacholine or LTD 4 , Bay K 8644 (10 μM) produced a further small contraction; Bay K 8644 (100 μM) relaxed the tissues below baseline. 3. 3. In tissues contracted with histamine, Bay K 8644 (10–100 μM) produced only relaxation. 4. 4. Bay K 8644 therefore has both Ca 2+ agonist and Ca 2+ antgonist properties, the calcium agonist activity is more pronounced in sensitized tissues.