- Catecholamines
- Ca influx via phosphorylation of Ca channels
- Ischaemia
- when intracellular Ca can't release more Ca from sarcolemma
- Hypocalcaemia (huh)
- Temperature
- ↓ myocardial sensitivity to calcium, and ↓ activity of actin-activated myosin ATPase
Treppe effect: ↑ contractility with ↑ HR
- Myocyte contraction is the consequence of significant calcium influx into the myocytes
- Relaxation is mainly due to this calcium being ejected back out of the cell, or re-sequestered into the sarcolemma
- This expulsion of calcium is a chemical process with a finite reaction time
- Ergo, with increased heart rate, the time left for the removal of calcium is decreased
- Ergo, the residual calcium will increase the contractility of the myocytes wherever a high heart rate is sustained.
- Not unique to cardiac myocytes