[Effect of caffeine and theophylline on Ca2+ sensitivity of troponin and Ca2+ release from SR in saponin-skinned rat cardiac muscle].
Cell membrane of cardiac muscle fiber (rat right ventricular papillary muscle) was chemically skinned (permeability of membrane increased) by treatment with saponin at low concentration (50 micrograms/ml), while the function of sarcoplasmic reticulum (SR) was preserved. The strength of rigor contraction of the skinned fiber was used as a semi-quantitative index of the ability of SR to release Ca2+. When treated with saponin at high concentration (500 micrograms/ml), both sarcolemma and membrane of SR were skinned. Tension-pCa relationship and the Ca2+ concentration required for producing 50% of maximum Ca(2+)-activated tension (pCa50) were respectively taken as qualitative and quantitative index of Ca2+ sensitivity of troponin (TN). The results showed: (1) In low saponin skinned fiber, 5 and 10 mmol/L caffeine respectively produced 89.2 +/- 12.7 and 142.5 +/- 17 mg (n = 4) rigor contraction, 5 mmol/L theophylline did not have this effect. (2) In high saponin skinned fiber 5 mmol/L theophylline, 5 and 10 mmol/L caffeine shifted the tension-pCa relationship curve to the left, pCa50 respectively increased by 0.212, 0.261 and 0.274 pCa units. These results suggest that caffeine and theophylline increase the Ca2+ sensitivity of TN and caffeine can also induce Ca2+ release from SR.
Huang
Y
Y
Laboratory of Cardiovascular Physiology, Hunan Medical University, Changsha.
He
Z H
ZH
Li
Y X
YX
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002317:Cardiovascular Agents / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D012503:Saponins; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013268:Stimulation, Chemical; D013806:Theophylline / Q000494:pharmacology*; D014336:Troponin / Q000378:metabolism*
D002317:Cardiovascular Agents; D012503:Saponins; D014336:Troponin; D002110:Caffeine; D013806:Theophylline; D002118:Calcium