Tris inhibits binding and transport of calcium in microsomal fraction isolated from rat vas deferens.
The effect of Tris on Ca2+ accumulation by microsomal membrane fraction isolated from rat vas deferens was studied. Preincubation with Tris of isolated microsomal membranes caused a dose-dependent inhibition of Ca2+ binding in the absence of ATP at low Ca2+ concentration (20 microM). This inhibitory effect of Tris on Ca2+ binding was not observed at high Ca2+ concentration (1 mM). Preincubation of membranes with Tris also resulted in decreased Ca2+ accumulation in the presence of ATP. Both ionomycin-sensitive and -insensitive components of the ATP-supported Ca2+ accumulation were significantly lower in membrane fraction preincubated with Tris than these in the control membrane fraction not treated with Tris suggesting that both Ca2+ binding and active transport of Ca2+ were affected by Tris. This was further supported by the fact that oxalate-stimulated ATP-supported Ca2- accumulation by the membrane was potently inhibited by Tris. This inhibition was more prominent when the membranes were preincubated with Tris. Efflux of Ca2+ into EGTA containing medium from a preloaded membrane fraction was not significantly different whether or not the membrane fractions were preincubated with Tris indicating that the membrane permeability to Ca2+ may not be altered by Tris. Our results provided direct evidence that Tris altered the Ca2+ binding and transport at the subcellular membrane level and may provide a cellular basis for the alterations of contractile function of vas deferens in the physiological saline solution buffered with Tris.
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000378:metabolism; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010070:Oxalates / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014325:Tromethamine / Q000494:pharmacology*; D014649:Vas Deferens / Q000378:metabolism
D010070:Oxalates; D014325:Tromethamine; D000255:Adenosine Triphosphate; D002118:Calcium