Calcium release from cardiac sarcoplasmic reticulum induced by photorelease of calcium or Ins(1,4,5)P3.
The ability of Ca2+ or inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] to release Ca2+ from cardiac sarcoplasmic reticulum (SR) was investigated using saponin-skinned ventricular trabeculae from rats. To overcome diffusion delays, rapid increases in the concentrations of Ca2+ and Ins(1,4,5)P3 were produced by laser photolysis of "caged Ca2+" (Nitr-5) and "caged Ins(1,4,5)P3". Photolysis of Nitr-5 to produce a small jump in [Ca2+] from pCa 6.8 to 6.4 induced a large and rapid force response (t1/2 = 0.89 s at 12 degrees C); the source of the Ca2+ that activated the myofibrils was judged to be the SR, since it was blocked by 0.1 mM ryanodine or 5 mM caffeine. A smaller, slower, and less consistent release of SR Ca2+ was produced by photorelease of Ins(1,4,5)P3. The results demonstrate that these caged compounds can be used to study excitation-contraction coupling in skinned multicellular preparations of cardiac muscle. The data are consistent with a major role for Ca2(+)-induced Ca2+ release in cardiac activation, whereas the role for Ins(1,4,5)P3 may be to modulate, rather than directly stimulate, SR Ca2+ release.
Kentish
J C
JC
National Institute for Medical Research, Mill Hill, London, United Kingdom.
Barsotti
R J
RJ
Lea
T J
TJ
Mulligan
I P
IP
Patel
J R
JR
Ferenczi
M A
MA
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism* / Q000494:pharmacology; D008027:Light; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013997:Time Factors
D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium