Mitochondria regulate inactivation of L-type Ca2+ channels in rat heart.
1. L-type Ca2+ channels play an important role in vital cell functions such as muscle contraction and hormone secretion. Both a voltage-dependent and a Ca2+-dependent process inactivate these channels. Here we present evidence that inhibition of the mitochondrial Ca2+ import mechanism in rat (Sprague-Dawley) ventricular myocytes by ruthenium red (RR), by Ru360 or by carbonyl cyanide m-chlorophenylhydrazone (CCCP) decreases the magnitude of electrically evoked transient elevations of cytosolic Ca2+ concentration ([Ca2+]c). These agents were most effective at stimulus rates greater than 1 Hz. 2. RR and CCCP also caused a significant delay in the recovery from inactivation of L-type Ca2+ currents (I(Ca)). This suggests that sequestration of cytosolic Ca2+, probably near the mouth of L-type Ca2+ channels, into mitochondria during cardiac contractile cycles, helps to remove the Ca2+-dependent inactivation of L-type Ca2+ channels. 3. We conclude that impairment of mitochondrial Ca2+ transport has no impact on either L-type Ca2+ currents or SR Ca2+ release at low stimulation frequencies (e.g. 0.1 Hz); however, it causes a depression of cytosolic Ca2+ transients attributable to an impaired recovery of L-type Ca2+ currents from inactivation at high stimulation frequencies (e.g. 3 Hz). The impairment of mitochondrial Ca2+ uptake and subsequent effects on Ca2+ transients at high frequencies at room temperature could be physiologically relevant since the normal heart rate of rat is around 5 Hz at body temperature. The role of mitochondria in clearing Ca2+ in the micro-domain near L-type Ca2+ channels could be impaired during high frequencies of heart beats such as in ventricular tachycardia, explaining, at least in part, the reduction of muscle contractility.
Sánchez
J A
JA
Department of Pharmacology, Cinvestav, AP 14-740, Mexico DF, 07300, Mexico.
García
M C
MC
Sharma
V K
VK
Young
K C
KC
Matlib
M A
MA
Sheu
S S
SS
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D007202:Indicators and Reagents / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017975:Ruthenium Compounds / Q000494:pharmacology; D012430:Ruthenium Red / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology
D020746:Calcium Channels, L-Type; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D010726:Phosphodiesterase Inhibitors; C112020:Ru 360; D017975:Ruthenium Compounds; D014475:Uncoupling Agents; D012430:Ruthenium Red; D002110:Caffeine; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002118:Calcium; D016257:Fura-2