Sufficiently high concentrations of cationic (n-alkyl trimethylammonium) or neutral (n-alkanols) amphipathic agents reduced the amplitude of maximum K
contractures of frog toe muscles, an effect which was antagonized by reduced temperature, by the presence of
perchlorate anions, or (to a lesser extent) by an increased concentration of
divalent cations. Enhancement of the similar effect of
tetracaine was prominent only with alkyl trimethylammonium compounds. Enhancement of the depressant effect of acidity (pH 5.0) was observed with octyl trimethylammonium and octanol but not with octanesulfonate or
butanol. Partial restoration of
potassium contractures in media lacking
divalent cations was produced by
octane- or
nonane-sulfonate and by
propanol but not by octyl trimethylammonium or octanol. The
alkyl sulfonates differed from the other agents studied in producing tonic
contractures at concentration which did not reduce maximum K-
contracture tension. The
alkyl sulfonates also differed from other amphipaths of similar size in their ability to elicit small repolarization-induced
contractures in the absence of
perchlorate, although this property also was shared by small alkanols. Sufficient concentrations of all amphipaths reduced the amplitude of repolarization-induced
contractures in the presence of
perchlorate. The intensity of the effects of these agents on contractile function usually was proportional to the size of their apolar group, and with ionic apmphipaths such effects were apparent only with compounds having
hydrocarbon chains containing eight or more
carbon atoms. These experiments indicate that hydrophobic interactions in the external lamina of the sarcolemma can influence the potential-dependent control of contractile function in skeletal muscle, presumably by effects on the conformational transitions of
integral membrane proteins.(ABSTRACT TRUNCATED AT 250 WORDS)