Abstract
The present study investigated the functional role of the sarcoplasmic reticulum Ca++-ATPase in contraction and relaxation, intracellular Ca++-transients, as well as on the force-frequency relationship in human myocardium. The Ca++-ATPase activity of membrane vesicles isolated from sarcoplasmic reticulum (SR) obtained from nonfailing donor hearts (n = 7) was measured in the presence of cyclopiazonic acid (CPA, 0–30 μM), a highly specific inhibitor of the Ca++-ATPase of the SR (SERCA). The effects of CPA on parameters of contraction and relaxation, force-frequency relationship and [Ca++]i transients (with fura-2) were studied on isolated left ventricular muscle strips from human nonfailing myocardium. CPA concentration-dependently inhibited SERCA activity of isolated SR vesicles. In the presence of CPA (30 μM) the former positive force-frequency relationship in human left ventricular nonfailing myocardium became negative. Especially at high frequencies of stimulation, CPA decreased developed tension, peak rate of tension rise and systolic fura-2-light emission, whereas time to peak tension, time to peak [Ca++]i, time to 95% relaxation, diastolic tension and diastolic Ca++ levels were increased. Peak rate of tension decay and time to half-relaxation and half-decay of [Ca++]i were not altered significantly after treatment with CPA. These findings provide evidence that the SERCA plays a functional role in the frequency-dependent increase in force of contraction in human myocardium. Because an impaired function of the SERCA is predominantly followed by alterations of inotropic and to a lesser degree of lusitropic function, other important factors to lower [Ca++]i and influence relaxation may be present in human myocardium to compensate for the reduced SERCA activity, e.g.,Na+-Ca++ exchanger.
Footnotes
-
Send reprint requests to: Dr.med. Robert H.G. Schwinger, Universität zu Köln, Medizinische Klinik III, Joseph-Stelzmannstr 9, D-50924 Köln, Germany.
-
↵1 Experimental work was supported by grants from the Deutsche Forschungsgemeinschaft (to R.H.G.S.) (Schw), the Zentrum für Molekulare Medizin Köln (grant from the Bundesministeriums für Bildung, Wissenschaft, Forschung und Technologie 1 KS 9501 to R.H.G.S.) and the Graduiertenkolleg für Molekulare Medizin der Universität zu Köln (to R.H.G.S.). This work contains data of the Doctoral Thesis of U.B., S.H. and B.B. (University of Cologne, in preparation). Part of the study was presented at the spring meeting of the American College of Cardiology in New Orleans, Louisiana (19–22 March 1995).
- Abbreviations:
- +T
- peak rate of tension rise
- −T
- peak rate of tension decay
- TPT
- time to peak tension
- T1/2T
- time to half relaxation
- T95T
- time to 95% relaxation
- SR
- sarcoplasmic reticulum
- SERCA
- SR-Ca++-ATPase
- CPA
- cyclopiazonic acid
- FFR
- force-frequency relationship
- I1/2I
- time at half decay of Ca++
- Isyst
- systolic light emission
- IPI
- time to peak Ca++
- Na2EDTA
- ethylenedinitrilotetraacetic acid disodium salt dihydrate
- AM
- acetoxymethyl
- EGTA
- ethyleneglycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- Received July 8, 1996.
- Accepted June 2, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
