EFFECTS OF SOME STEROID AND NONSTEROID LACTONES ON POTASSIUM EXCHANGE AX!) IHYSIOLOGICAL PROPERTIES OF THE ISOLATED PERFUSED GUINEA PIG VENTRICLE’

lii a previous study (Vick and Kahnm, 1957) evio!ence was presente(! that conmtracture is re-late! to the o!irectionm of mmet movemument of potas-siumu in the isolated perfused guinea pig ventricle. AIm increasing or sustained oontracture was ac-companied by net loss of potassiunm, while dIe-creasing contracture was accomumpanied by a net uptake of potassiunu by time imeart. Ouabain, wimich can cause commtracture mmthus preparation, inihiibits the net uptake of l)otassiunuu by time heart, causinmg a loss of that ionm (Vick and! Kahn, 1957). Ouahain also inhibits time mmet uptake of potassium mm Imuman erythirocytes (Kalmn and Acheson, 1955), anol this effect is shareo! by certain non-steroio! lactonues (Kahmmi, 1957). We wished to study the effects o)f the latter on time hieart. If these lactones affect potassium exciiange of the imeart as ouabain does, they should cause the hmeart to lose potassium, and timerefore allow a test of time hypothesis that comitraeture is depenmdent upon potassiunm loss. Timey nmuigimt also prod!uce other effects of caroliac glyoosides, like the posi-tive inmotropic effect, if this is also related to the olecrease in internal Potassium (Hajdu, 1953). Jim earlier studies simple unsaturateol lactones caused contracture in time isolated frog heart (Krayer et al., 1942; Cimen et al, 1942; Giarman, 1948) preceoled by a positive inotropic effect whuenu time preparationm was inypodymmamic (Krayer ci al, 1942; Giarman, 1949). Timese effects were like timose prodluoedl by time cardhac glycosides. When studhed in certaimi mammuiahiamm preparations (Chiemm ci al., 1942; Waltomm el al., 1950) tIme lac-tonmes (lid not produce effects like timose of the earoliac glycosides. In none of tIme work citeo! was This investigation was sunppo)rted by grant