Properties of cardiac I(leak) induced by photosensitizer-generated reactive oxygen.
We reported previously that photomodification of single frog cardiac cells by Rose Bengal induces a time-independent current, designated I(leak)++, having a linear current-voltage (I/V) relationship. The purpose of the present study is to better characterize the properties of I(leak)++. Initially, I(leak)++ has a reversal potential (ER) near -70 mV, but with time, ER shifts toward a final value near 0 mV. This shift in ER is accompanied by a marked increase in conductance (slope of I/V relationship). Evidence is presented that the depolarizing shift in ER with time during photomodification results from a loss of membrane selectivity allowing sodium to make an increasing contribution to I(leak)++. Potassium also contributes to I(leak)++, as indicated by marked depolarizing shifts in ER following replacement of intracellular potassium with either cesium or tetraethylammonium. Since these results occur in calcium-free external media, the depolarizing shifts in ER and increased conductance are not related to activation of a calcium-dependent nonselective cation channel. However, I(leak) does have some properties similar to nonselective cation currents recently reported to be activated by membrane breakdown products such as arachidonic acid and lysophosphoglycerides.
Tarr
M
M
Department of Physiology, University of Kansas Medical Center, Kansas City 66160-7401.
Arriaga
E
E
Goertz
K K
KK
Valenzeno
D P
DP
D000818:Animals; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity / Q000187:drug effects; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D011898:Ranidae; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D012395:Rose Bengal / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors
D007473:Ion Channels; D017382:Reactive Oxygen Species; D013757:Tetraethylammonium Compounds; D002586:Cesium; D012395:Rose Bengal; D019789:Tetraethylammonium; D011188:Potassium