Leucine-enkephalin increases the level of inositol (1,4,5) triphosphate and releases calcium from an intracellular pool in rat ventricular cardiac myocytes.
In rat ventricular cardiomyocytes loaded with the fluorescent Ca2+ indicator Indo-1/AM, the delta opioid receptor agonist Leu-Enk caused Cai oscillations and abolished the caffeine-induced Cai transient. During superfusion of cardiomyocytes with the specific opioid antagonist naloxone, Cai is not affected by Leu-Enk and the caffeine-triggered Cai transient is preserved. In parallel experiments with cardiac myocytes, the delta opioid agonist increased the intracellular level of Ins (1,4,5) P3 by about 4 times above the control value. Such an effect was completely antagonized by naloxone. Thus, Leu-Enk induces depletion of Ca2+ from the SR by a receptor-mediated mechanism which appears to involve an increase in the intracellular level of Ins (1,4,5) P3.
Ventura
C
C
Istituto di Chimica Biologica, Facoltà di Medicina e Chirurgia, Università di Sassari.
Lakatta
E G
EG
Sisini
A
A
Campus
M P
MP
Capogrossi
M C
MC
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis*; D007424:Intracellular Fluid / Q000737:chemistry; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects* / Q000502:physiology; D017465:Receptors, Opioid, delta; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D015290:Second Messenger Systems / Q000187:drug effects*
D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D012433:Ryanodine; D009270:Naloxone; D002110:Caffeine; D004743:Enkephalin, Leucine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium