The origin of MAP has not yet been explained sufficiently. Former ideas were based on ‘discharging’ of the membrane potassium battery by an increase of potassium permeability during the introduction of positive or negative pressure . This view accounted only for electrical changes and did not take into account mechanical changes such as stretching of tissue and of the cell membrane in particular .
Undoubtedly, pressure or suction of the tip electrode against the myocardium depolarizes the region beneath the electrode and, according to current opinion, renders it inex-citable for as long as the pressure is maintained. The depolarized region should serve as a reference of normally unavailable, constant electrical potential . However, this concept does not agree with our observation that the typical cardiac action potential under the suction electrode can be recorded with an intracellular microelectrode in partially and reversibly depolarized myocytes during the first 5 to 6 mins of suction at-40 kPa . Rather, the application of suction resembles the ‘loose patch recording’ used for the study of large excitable cells, such as muscle fibres , or recordings by the contact electrode method. Cheapest drugs online – buy ventolin inhalers for you to spend less money every time.