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Unexpected contractile response from the G-protein activator mastoparan in cardiac myocytes
1Department of Biochemistry, Dr Karl Thomae GmbH, Biberach an der Riss, Germany.
Abstract:
Mastoparan preferentially activates the G protein Gi in transmembrane signalling pathways. In heart tissue Gi couples receptors to negative inotropy so we have examined the effect of mastoparan on contractility in cardiac myocytes electrically stimulated at 0.5 Hz. Mastoparan (10(-5) mol/l) caused a time-dependent increase in cell shortening to a maximum of 83.7 +/- 18.0% (n = 7) of the resting cell length at between 4 and 7 min. This could be the result of either stimulation of other G proteins or the release of beta gamma subunits from Gi which activate phospholipase C.
Insights
Mastoparan, a G protein-activating peptide, was studied for its effects on cardiac myocyte contractility. Results showed mastoparan increased cell shortening, suggesting potential roles in cardiac signaling pathways.
Area of Science:
- Pharmacology
- Cellular Biology
- Cardiovascular Physiology
Background:
- Mastoparan is known to activate the inhibitory G protein Gi in transmembrane signaling.
- In cardiac tissue, Gi-coupled receptors typically mediate negative inotropic effects.
Purpose of the Study:
- To investigate the effect of mastoparan on the contractility of cardiac myocytes.
- To explore the potential mechanisms underlying mastoparan's action in the heart.
Main Methods:
- Primary cardiac myocytes were electrically stimulated at 0.5 Hz.
- The effect of mastoparan (10^-5 mol/L) on cell shortening was measured over time.
Main Results:
- Mastoparan induced a time-dependent increase in cardiac myocyte cell shortening.
- Maximum cell shortening reached 83.7 +/- 18.0% of resting length between 4 and 7 minutes.
- This effect suggests a complex interaction with G protein signaling pathways.
Conclusions:
- Mastoparan enhances cardiac myocyte contractility, contrary to the typical Gi-coupled receptor effect.
- The observed increase in contractility may involve alternative G protein activation or Gi beta-gamma subunit release leading to phospholipase C activation.