Action of heptaminol hydrochloride on contractile properties in frog isolated twitch muscle fibre.

1 Heptaminol stopped or delayed the progressive decline in tension which characterizes the phenomenon of fatigue in frog isolated twitch muscle fibre. 2 Heptaminol had no action on the sodium, potassium and calcium voltage-dependent ionic conductances. 3 The hypothesis of an action via an internal alkalinization was tested by comparison with the action of NH4Cl. Both substances increased the tension. 4 The action of heptaminol was suppressed in sodium-free (TRIS) solution or in the presence of amiloride while the action of NH4Cl was always observed. 5 These results could be explained by a stimulation of the Na/H antiport by heptaminol.