Evidence against a role of (Na++K+-ATPase in the alpha-adrenoceptor mediated positive inotropic effect of phenylephrine

Phenylephrine (0.1–100 μM) in the presence of 1 μM propranolol increased the force of contraction in electrically driven papillary muscles from cats. This presumably alpha-adrenoceptor mediated positive inotropic effect of phenylephrine occurred without any influence on (Na++K+-ATPase activity.