Mode of action of diethyl ether on ATP-dependent Ca2+ transport by sarcoplasmic reticulum vesicles

The mode of action of diethyl ether on the sarcoplasmic reticulum Ca2+ pump and ATPase activity was investigated in sarcoplasmic reticulum vesicles (SR). The addition of ether (5%, v/v) at 23 degrees nearly doubled the rates of ATP-dependent Ca2+ uptake and ATP hydrolysis by SR for a wide range of ATP concentrations (20 microM to 10 mM). By contrast, the Ca2+-independent ATPase activity of SR decreased with increasing ether concentrations and practically ceased at higher ether solutions (5-7%, v/v). Ether not only enhanced the forward transport of Ca2+ into vesicles but also the reversal of the Ca2+ pump, and higher rates of Ca2+ efflux coupled to ATP synthesis were observed from Ca2+-loaded vesicles. Electron micrographs of SR pellets showed that the average radius of the vesicles increased by about 20% upon exposure to ether. In the range of 5-40 degree the rate of Ca2+ transport increased with temperature; at about 4 degrees active Ca2+ transport by SR normally ceased, but with the addition of ether (5%, v/v) significant Ca2+ transport (1-2 nmoles Ca2+ per mg per sec) occurred at 0 degree. The further stimulation of SR Ca2+ transport induced by ether was particularly effective at low temperatures; ether increased the rate of Ca2+ uptake by a factor of 10 at 5 degrees but only by a factor of 1.5 at 40 degrees. The effect of ether on the (Ca2+-Mg2+)ATPase of SR could be reversed by resuspending the vesicles in ether-free media. The centrifugation and resuspension of SR in ether-free solutions did not make the vesicles leaky nor did it lyse them irreversibly unless they were also mechanically disrupted. The results indicate that, in ether, there was an increase of intravesicular volume and an increase in membrane fluidity of SR, which could account for the dramatic increase in Ca2+ capacity and rate of Ca2+ transport of ether-treated SR.