Silver ions induce Ca2+ release from the SR in vitro by acting on the Ca2+ release channel and the Ca2+ pump.
Silver nitrate (AgNO3) is a sulfhydryl oxidizing agent that induces a biphasic Ca2+ release from isolated sarcoplasmic reticulum (SR) vesicles by presumably oxidizing critical sulfhydryl groups in the Ca2+ release channel (CRC), causing the channel to open. To further examine the effects of AgNO3 on the CRC and the Ca2+-ATPase, Ca2+ release was measured in muscle homogenates prepared from rat hindlimb muscle using indo 1. Cyclopiazonic acid (CPA) and ruthenium red (RR) were used to inhibit the Ca2+-ATPase and block the CRC, respectively, before inducing Ca2+ release with both AgNO3 and 4-chloro-m-cresol (4-CMC), a releasing agent specific for the CRC. With AgNO3 and CPA, the early rapid rate of release (phase 1) was increased (P < 0.05) by 42% (314 +/- 5 vs. 446 +/- 39 micromol x g protein(-1) x min(-1)), whereas the slower, more prolonged rate of release (phase 2) was decreased (P < 0.05) by 72% (267 +/- 39 vs. 74 +/- 7.7 micromol x g protein(-1) x min(-1)). RR, in combination with AgNO3, had no effect on phase 1 (P > 0.05) (314 +/- 51 vs. 334 +/- 43 micromol x g protein(-1) x min(-1)) and decreased phase 2 (P < 0.05) by 65% (245 +/- 34 vs. 105 +/- 8.2 micromol x g protein(-1) x min(-1)). With 4-CMC, CPA had no effect (P > 0.05) on either phase 1 or 2. With addition of RR, phase 1 was reduced (P < 0.05) by 59% (2,468 +/- 279 vs. 1,004 +/- 87 micromol x g protein(-1) x min(-1)), and RR completely blocked phase 2. Both AgNO3 and 4-CMC fully inhibited Ca2+-ATPase activity measured in homogenates. These findings indicate that AgNO3, but not 4-CMC, induces Ca2+ release by acting on both the CRC and the Ca2+-ATPase.
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Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004396:Coloring Agents / Q000494:pharmacology; D003408:Cresols / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D018482:Muscle, Skeletal / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012430:Ruthenium Red / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D012835:Silver Nitrate / Q000494:pharmacology*
D015220:Calcium Channels; D004396:Coloring Agents; D003408:Cresols; D012430:Ruthenium Red; C006984:chlorocresol; D012835:Silver Nitrate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium