Abstract
Ca 2+ efflux, Ca 2+-ATPase, and membrane permeability measurements were used to investigate the biochemical mechanisms of Ca 2+ release induced by mastoparan (MP) and the chimeric hormone-MP constructs incorporating galanin (galparan) or vasopressin antagonist (M375 and M391) moieties. Comparative studies utilised preparations of porcine cerebellar microsomes and rabbit skeletal muscle sarcoplasmic reticulum (SR). MP and chimeric peptides galparan, M375 and M391 induce Ca 2+ release over a range of concentrations from 0.3–10 μM. Comparison of MP and three chimeric, N-terminal extended, constructs indicates that N-terminal extension modifies the biological properties of MP, producing changes in efficacy which are enzyme-isoform-specific. Biochemical studies indicate that the chimeric analogues and MP inhibit Ca 2+-ATPases and directly activate the ryanodine receptor (RyR) to release Ca 2+ from both heavy SR (HSR) and microsomes. The same peptides have no effect on the InsP 3 receptor (InsP 3R). Other actions that include modest changes in membrane permeability may also contribute to the Ca 2+-mobilising action of MP and chimeric constructs.
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