Comparison of the Effects of Calcium and the Calcium Channel Stimulant Bay k 8644 on Neomycin‐Induced Neuromuscular Blockade

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Abstract
The effects of calcium and the calcium channel stimulant Bay k 8644 on neomycin‐induced neuromuscular blockade were evaluated using rat phrenic nerve‐hemidiaphragm preparationsin vitro.Neomycin showed maximum potency in inducing neuromuscular blockade when the calcium concentration in the bath was 1 mM. Higher calcium concentrations (1.5, 2 and 4 mM) produced a gradual decrease in neomycin potency, manifested as a progressive shift to the right of neomycin concentration‐response curves. Bay k 8644 (0.1 and 1 μM) did not significantly modify indirectly elicited diaphragm contractionsper se, nor did it antagonize neomycin‐induced neuromuscular blockade. A higher concentration of Bay k 8644 (10 μM) antagonized indirectly elicited contractions. In conclusion, our results show that Bay k 8644, at concentrations causing calcium channel stimulation at the cardiac and vascular level, did not exert stimulant effects in a nerve‐skeletal muscle preparation, suggesting that its action may be tissue‐selective to a certain degree.