Increase in calcium leak channel activity by metabolic inhibition or hydrogen peroxide in rat ventricular myocytes and its inhibition by polycation.
Ca influx in cultured neonatal myocardium can be augmented by metabolic inhibition or free radical exposure. This increase cannot be prevented by blockade of L-type Ca channels or inhibition of Na-Ca exchange. It is speculated that a specific Ca leak may be involved in this process. In the present study patch clamp techniques were used to examine this hypothesis. Currents were measured in a recording configuration of cell attached or excised inside-out membrane patches in adult rat ventricular myocytes as affected by metabolic inhibition or free radical exposure. The metabolic inhibition was achieved by use of 1 mM iodoacetic acid and 10 mM 2-deoxyglucose with omission of glucose in the perfusate. Free radicals were generated by application of 100 microM hydrogen peroxide in the perfusate. Specific Ca leak channels were identified. The channels were not significantly permeable to monovalent cations. The activity of these channels was increased markedly over a period of minutes by metabolic inhibition or free radical exposure. In the presence of 100 microM hydrogen peroxide the open probability (NPo) of the channels increased from 0.0083 +/- 0.003 (mean +/- S.D.) in control to 0.09 +/- 0.024 (P < 0.01). During metabolic inhibition it was augmented from 0.0075 +/- 0.0035 to 0.062 +/- 0.018 (P < 0.01). The increase of the Ca leak channel activity under both conditions could be completely blocked by addition of polycationic protamine to the patch pipette solution. The results support the hypothesis that Ca leak channels are involved in the Ca overload induced by metabolic inhibition or free radical exposure. The inhibitory effect of polycation may have important therapeutic implications for the treatment of ischemic cardiac heart disease.
Wang
S Y
SY
Cardiovascular Research Laboratories, UCLA School of Medicine 90024-1760, USA.
Clague
J R
JR
Langer
G A
GA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004734:Energy Metabolism; D005609:Free Radicals; D006321:Heart / Q000187:drug effects; D006352:Heart Ventricles; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011479:Protamines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D015220:Calcium Channels; D005609:Free Radicals; D011479:Protamines; D006861:Hydrogen Peroxide; D002118:Calcium