High sensitivity of chicken's skeletal muscle sarcoplasmatic reticulum to effects of diltiazem or verapamil on calcium uptake and release.
In this study, the effects of two different calcium channel blockers, diltiazem and verapamil on calcium uptake and release from the membrane of heavy sarcoplasmic reticulum (SR) of chicken skeletal muscle were investigated. A fluorescent chelate probe technique was employed to determine calcium movement through the SR. Chlortetracycline was used as a fluorescent indicator which is able to penetrate the membrane, bind to the calcium on the inner face of the membrane and show an increase in fluorescence intensity when calcium uptake occurs. Addition of tris-ATP to the microsomes caused ATP-induced calcium uptake in a concentration dependent manner with half-maximal calcium uptake around 0.126 mM. Pretreatment of the medium containing sarcoplasmic reticulum with different concentrations of diltiazem or verapamil followed by added tris-ATP resulted a significant decrease in the fluorescence intensity of chlortetracycline, showing that these calcium channel blockers can diminish ATP-induced calcium uptake in a concentration-dependent manner. The maximum fluorescence intensity of tris-ATP falls to 50% in the presence of 1.75 microM diltiazem and 25 nM verapamil. In addition, diltiazem and verapamil can significantly induce rapid calcium release from the membrane of sarcoplasmic reticulum in a concentration-dependent manner. Therefore, membrane-bound or sequestered calcium in the sarcoplasmic reticulum may be targeted by these two calcium channel blockers in chicken skeletal muscle. Chicken SR is about 1000 times more sensitive to the effects of diltiazem on Ca2+ uptake and release than rabbit SR as shown previously.
Mirazi
N
N
Department of Biology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. mirazi@basu.ac.ir
Paydar
M J
MJ
Vali
L
L
Dehpour
A R
AR
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002645:Chickens / Q000378:metabolism*; D002751:Chlortetracycline / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology*; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008856:Microscopy, Fluorescence; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D000255:Adenosine Triphosphate; D014700:Verapamil; D004110:Diltiazem; D002118:Calcium; D002751:Chlortetracycline