Dethiophalloidin increases Ca super(2+) responsiveness of skinned cardiac muscle

• Published in: Journal of muscle research and cell motility 1998-06, Vol.19 (5), p.515-523
• Main Authors: Bukatina, A E, Kirkpatrick, R D, Campbell, K B
• Format: Article
• Language: English
• ISSN: 0142-4319

Phalloidin, an F-actin stabilizing peptide, is known to enhance Ca super(2+) responsiveness in skinned cardiac muscle. Here we studied the effects of dethiophalloidin (DTPH), a phalloidin derivative which, binding much more weakly to F-actin, has no phalloidin-specific ability to stabilize F-actin, on skinned bovine left ventricle muscle. When added to activated skinned muscle, DTPH (15-80 mu M), similarly to phalloidin, caused a rapid (within several minutes) enhancement of active force; the relative force enhancement by DTPH became greater as Ca super(2+) concentration was decreased. Unlike phalloidin, DTPH effects were reversible. Using a value of the force enhancement at 15 mu M DTPH (76% of maximum), an apparent equilibrium constant for DTPH binding to myofilaments was estimated at about 5 mu M. Force-pCa plots showed that DTPH (80 mu M) brought about a 10% increase in the maximal Ca super(2+)-activated force and a 0.34 pCa units increase in the Ca super(2+) sensitivity. Both changes are stronger than those caused by phalloidin in similar conditions (6% and 0.2 pCa units, respectively). As with phalloidin, DTPH did not change the value of the Hill coefficient in the fit to the force-pCa curve. DTPH and phalloidin interacted as follows: (1) pre-treatment with phalloidin entirely prevented the response to DTPH, indicating the absence of any non-specific DTPH action; and (2) when added after DTPH, phalloidin decreased the force enhancement due to DTPH, reflecting a stronger effect of DTPH to increase force. In conclusion, the stabilization of F-actin structure is not a major factor in the mechanism by which phalloidin modifies contraction.