Photomodification of cardiac membrane: chaotic currents and high conductance states in isolated patches.
We have demonstrated previously that photomodification permeabilizes cardiac cells as evidenced by activation of a whole-cell leak current. In this paper we report that photomodification induces in cell-attached and inside-out cardiac membrane patches a chaotic current. Unlike current recordings from many protein ion channels that show stepwise amplitude changes associated with open and closed states of the channel, the chaotic current consists of variable amplitude spike-like transitions. The amplitudes of these spikes can vary from tenths to tens of picoamperes at a constant transmembrane potential. We provide evidence that the chaotic current is transmembrane rather than trans-seal and has a voltage dependency expected for current flow through nonspecific conductance pathways. Photomodification can also induce high conductance states (greater than 500 pS) in cell-attached and inside-out patches. We present evidence that the high conductance state is also not related to seal breakdown. Our results suggest that both the chaotic current activity in and high conductance state of photomodified cardiac membrane patches result from the opening of many small conductance, nonspecific pathways through the membrane.
Tarr
M
M
Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City 66160-7401, USA. mtarr@kumc.edu
Valenzeno
D P
DP
D000818:Animals; D002462:Cell Membrane / Q000502:physiology / Q000528:radiation effects*; D004553:Electric Conductivity; D006321:Heart / Q000502:physiology*; D006325:Heart Atria; D008027:Light; D008564:Membrane Potentials / Q000528:radiation effects; D017711:Nonlinear Dynamics; D018408:Patch-Clamp Techniques; D011898:Ranidae