Ca2+ loading reduces the tensile strength of sarcolemmal vesicles shed from rabbit muscle.
1. Sarcolemmal vesicles shed by rabbit muscle were loaded with Ca2+ by means of A23187 or ionomycin. [Ca2+]0 was buffered between 0.8 and 20 microM. Membrane strength was measured by pipette aspiration. 2. At 20 microM Ca2+ many vesicles underwent autolysis, or were so weak that they burst instantly on aspiration. Between 10 and 2 microM Ca2+ a graded decrease in membrane strength was demonstrable. At 0.8 microM Ca2+ the mechanical properties of the sarcolemma remained unaltered. 3. Mg2+ carried by A23187 does not mimic the effect of Ca2+. The ionophore itself similarly did not cause a decrease in membrane tensile strength. 4. Pre-treatment with BAPTA-AM, so as to buffer internal Ca2+, partly protected vesicles against the decrease in membrane strength produced by Ca2+ loading. 5. Membrane strength was not restored by adding excess BAPTA to the bathing solution, so as to reverse the Ca2+ gradient. An irreversible degradation of the membrane consequent upon raised [Ca2+]1 seems indicated. 6. These findings are discussed in relation to the mechanisms which have been advanced to account for the role of elevated [Ca2+]1 in cell death. 7. An attempt to use staphylococcal alpha-toxin as an alternative means to permeabilize the sarcolemma led to the incidental finding that this pore-forming protein itself greatly weakens the membrane in doses lower than required for effective permeabilization.
Nichol
J A
JA
Institute of Physiology, University of Glasgow, UK.
Hutter
O F
OF
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D016658:Psoas Muscles / Q000502:physiology*; D011817:Rabbits; D012508:Sarcolemma / Q000378:metabolism / Q000502:physiology*; D013718:Tensile Strength / Q000187:drug effects; D010738:Type C Phospholipases / Q000494:pharmacology
D002614:Chelating Agents; D007476:Ionophores; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D000001:Calcimycin; D004533:Egtazic Acid; D015759:Ionomycin; D010738:Type C Phospholipases; D002118:Calcium