Abstract 15866: Size and Ionic Currents of Unexcitable Cells Coupled to Cardiomyocytes Distinctly Modulate Cardiac Action Potential Shape and Pacemaking Activity
Potential electrical coupling between cardiomyocytes (CMs) and endogenous or exogenously added unexcitable cells can profoundly alter cardiac action potential (AP) initiation, shape, and conduction. To dissect how size and ionic currents of unexcitable cells modulate cardiac AP shape and pacemaking, we micropatterned cell pairs consisting of a CM coupled to a monoclonally derived HEK-293 cell of varying size (Fig A) engineered to express RFP and either connexin-43 (Cx43 HEK) or Kir2.1 and connexin-43 (Kir2.1+Cx43 HEK). By fixing micropatterned cell-cell contact length at 19.6±1.3 µm, the coupling strength was set to 68.9±9.7 nS. Independent of cell size, the resting potentials of Cx43 HEKs and Kir2.1+Cx43 HEKs were -26.5±1.9 and -72.7±0.8 mV, respectively. With increase of Cx43 HEK size, CM resting potential increased from -71.7±0.6 mV in single CMs to -35.1±1.3 mV in pairs with HEK:CM area ratio of 1.7±0.1 (Fig B), while (dVm/dt)max decreased to 1.6±0.7% (Fig C) and APD increased to 177±32% (Fig D) of the single CM values, respectively. Pacemaking activity was found in all Cx43 HEK-CM pairs with area ratios 1.08-1.94 (n=25) with a biphasic dependence of beating rate on HEK size (Fig E). In contrast, CMs coupled with Kir2.1+Cx43 HEKs of increasing size had similar resting potentials of -70.7±1.0 mV, exhibited no spontaneous activity, and showed gradual decrease in APD (to 74±8.7% of single CM value at HEK:CM area ratio of 1.9±0.1). Furthermore, APs were also recorded in single CMs connected via dynamic clamp to a software model of either unexcitable cell capacitance alone or capacitance with corresponding experimentally derived membrane ionic current (Fig B-E). From these experimental and modeling studies, we conclude that increase in unexcitable cell size strongly decreases (dVm/dt)max and increases duration of the cardiac AP, while unexcitable cell ionic currents further modulate (dVm/dt)max and APD and determine CM resting potential and pacemaking activity.
- © 2011 by American Heart Association, Inc.