L-TYPE CALCIUM CURRENT IN HUMAN VENTRICULAR MYOCYTES AT A PHYSIOLOGICAL TEMPERATURE FROM CHILDREN WITH TETRALOGY OF FALLOT

Objective: The aim was to investigate the electrophysiological propert ies of the L-type calcium current (I-Ca,I-L) in ventricular myocytes a t a physiological temperature (36-37 degrees C) isolated fl sm childre n undergoing surgical repair of tetralogy of Fallot, Methods: I-Ca,I-L , was recorded with the patch-clamp technique in the single electrode whole-cell mode at a physiological calcium concentration(1.8 mmol/l) a t 36-37 degrees C. Results: Under these conditions, maximum current de nsity averaged -5.80 +/- 0.45 pA/pF. I-Ca,I-L, showed a bell-shaped cu rrent-voltage relationship: the curl ent activated at - 37.7 +/- 1.36 mV. peaked at + 9.31 +/- 1.60 mV and reversed at + 57.7 +/- 2.17 mV (n = 17). At +10 mV. time to peak of I-Ca,I-L, was 5.23 +/- 0.46 ms. mem brane potentials for half-maximal steady-state activation and inactiva tion of I-Ca,I-L were - 6.02 and - 20.4 mV, respectively, the slope fa ctors were 7. 16 mV for steady-state activation and 6,49 mV for steady -state inactivation. I-Ca,I-L, did not completely inactivate and showe d a big window current between:cen -45 and + 40 mV. The inactivation o f I-Ca,I-L showed a biexponential time course with a fast time constan t ranging from 9.11 to 12.9 ms and a slow time constant ranging from 6 0.9 to 220 ms between - 30 and + 30 mV. Only the slow time constant sh owed a pronounced voltage dependency. The recovery from inactivation o f I-Ca,I-L was biphasic with a fast time constant of 60.7 ms and a slo w time constant of 619 ms. beta-Adrenergic stimulation with isoprenali ne (1 mu mol/l) increased the I-Ca,I-L density from - 5.71 +/- 1.55 to - 13.8 +/- 1.96 pA/pF (142%; P < 0.05) at + 10 mV. Conclusions: The p resent study demonstrates that most of the electrophysiological proper ties of I-Ca,I-L in ventricular myocytes isolated from children with t etralogy of Fallot resemble those of adult ventricular cells. The exis tence of a big calcium window current could be involved in the occurre nce of early afterdepolarizations which could lead to the high inciden ce of arrhythmias after. surgical repair of tetralogy of Fallot. (C) 1 998 Elsevier Science B.V. AII lights reserved.