Effects of intracellular calcium elevation on action potential and L-type calcium current of normal and chronically infarcted rat ventricles.
The present work investigated the effects of raising [Ca+2]i levels on action potential (AP) and L-type calcium current (I(Ca.L)) of normal and chronically infarcted rat ventricles. Experiments were performed by conventional electrophysiology and whole-cell patch-clamp techniques. In the former, APs were recorded in ventricular strips subjected to different pacing rates or elevation of [Ca+2]o levels. In the latter, I(Ca.L) was studied in isolated myocytes in the absence of an intracellular Ca+2 chelator. The acceleration of heart rate (6 to 240 beats/min) reduced AP duration measured at 20%, 50%, and 90% repolarization (APD20, APD50, and APD90) in the infarcted group, and increased APD20 and APD50 in the control group. Rising [Ca+]o (1.25 to 5.0 mmol/L) induced a decrease of APD20 and APD50 in both groups. Voltage clamp revealed a smaller I(Ca.L) density at approximately -17 mV in myocytes from infarcted ventricles (-1.86 +/- 0.37 vs -3.98 +/- 0.65 pA/pF, P < .05), and the appearance of a non-K+ outward current coupled to I(Ca.L). The results suggest the participation of a Ca+2-activated outward current in the repolarization of normal and infarcted rat ventricles.
Lima
Z F
ZF
Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brazil.
de Brito Santos
P E
PE
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002312:Cardiomyopathy, Hypertrophic / Q000503:physiopathology*; D002712:Chlorides / Q000502:physiology; D003627:Data Interpretation, Statistical; D004594:Electrophysiology; D005260:Female; D006352:Heart Ventricles / Q000166:cytology / Q000503:physiopathology*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009203:Myocardial Infarction / Q000378:metabolism / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar
D020746:Calcium Channels, L-Type; D002712:Chlorides; D002118:Calcium