Modelling the Effect of Intracellular Calcium in the Rundown of L-Type Calcium Current

The L-type calcium current
$(I_{CaL})$
is a key current of the heart playing an important role in the contraction of the cardiomyocyte. Patch-clamp recordings of ionic currents can be associated with a reduction of the current magnitude with time (termed ‘rundown’), and this phenomenon is particularly pronounced for
$I_{CaL}$
recordings. Some part of rundown can be attributed to the unique sensitivity of L-type calcium channels (LCCs) to local
$[Ca^{2+}]$
. In this paper, we study the experimental conditions in which rundown due to calcium-dependent inactivation
$(CDI)$
is minimised. We use first principles to derive an analytical equation for the diffusion of a calcium-chelating buffer from a patch hole on the cell's surface to the entirety of the cell. This determines the concentration profile of the buffer with respect to time and space. We then use the equation to simulate the effects of incoming calcium via the LCCs and its chemical reaction with the buffer.