Bathmotropic
Bathmotropic often refers to modifying the degree of
While bathmotropic, as used herein, has been defined as pertaining to modification of the excitability of the heart, it can also refer to modification of the irritability of heart muscle, and the two terms are frequently used interchangeably.[3]
Etymology
The term "bathmotropic" is derived from the Ancient Greek word βαθμός (bathmós), meaning "step" or "threshold".[citation needed]
History
In 1897
Physiological explanation
The bathmotropic effect modifies the heart muscle membrane excitability, and thus the ease of generating an
During stage 4 of an action potential, the inside of a cardiac muscle cell rests at −90 mV. As the inner muscle cell potential rises towards −60 mV, electrochemical changes begin to take place in the voltage-gated rapid sodium channels, which permit the rapid influx of sodium ions. When enough sodium channels are opened, so that the rapid influx of sodium ions is greater than the tonic efflux of potassium ions, then the resting potential becomes progressively less negative, more and more sodium channels are opened, and an action potential is generated. The electrical potential at which this occurs is called the threshold potential.[citation needed]
As various drugs and other factors act on the resting potential and bring it closer to the threshold potential, an action potential is more easily and rapidly obtained. Likewise, when the sodium channels are in a state of greater activation, then the influx of sodium ions that allows the membrane to reach threshold potential occurs more readily. In both instances, the excitability of the
Drugs, ions and conditions
Increasing bathmotropy
- sodium channels which prevents depolarization, so decreases in calcium allow increased sodiumpassage and which lowers the threshold for depolarization.
- Mild to moderate hyperkalemia[9] - causes a partial depolarization of the resting membrane potential
- Norepinephrine[10] and sympathetic stimulation in general - raises the resting membrane potential
- Digitalis - Converts the normal Purkinje action potential of heart muscle to the automaticity type, which increases myocardial irritability
- Epinephrine- Also known as adrenaline, effects are similar to sympathetic stimulation
- Mild hypoxia - causes a partial depolarization of the muscle membrane
- Ischaemia - causes a partial depolarization of the muscle membrane
Decreasing bathmotropy
- Hypercalcemia[8]- decreases permeability to sodium, hyperpolarizes membrane.
- Propranolol[11]
- Antiarrhythmic agents- block the voltage gated sodium channels
- Calcium channel blockers - in general have negative bathmotropic effects
- Parasympatheticstimulation - decreases excitability only of atrial muscle cells
- Hyponatremia - decreases external sodium concentration
- Hypokalemia[12] - hyper polarization of the resting membrane potential
- Acetylcholine - same as parasympathetic stimulation
- Marked hypoxia- causes a marked depolarization of the resting membrane potential
See also
References
- ^ Miriam Webster's Medical Dictionary and Online Medical Dictionary
- ^ "The Kanji Foundry Press - b". Archived from the original on 2008-03-12. Retrieved 2008-05-14.
- ^ "Bathmotropy".
- S2CID 31891993.
- PMID 6220901.
- ^ The American Journal of the Medical Sciences. J.B. Lippincott, Company. 1908. pp. 46–.
- ^ Scientific American Medical; Dale and Federman Vol 1; 2003 Edition p. 1907 chapter 160; Disorders of Acid-Base and Potassium Balance
- ^ PMID 10097179.
- PMID 16243117.
- PMID 11428819.
- S2CID 26706163.
- ^ Hypokalemia
