UNIFORMITY OF CALCIUM-CHANNEL NUMBER AND ISOMETRIC CONTRACTION IN HUMAN RIGHT AND LEFT-VENTRICULAR MYOCARDIUM

We compared contractile performance in trabeculae carneae (n = 25) fro m non-failing right and left ventricles (n = 25) of brain dead organ d onors without known cardiovascular disease and measured connective tis sue content in trabeculae carneae from both non-failing and failing hu man hearts. Peak twitch force and time-course of contraction were not different between muscles taken from right or left ventricles. Peak tw itch force was 13.9 +/- 3 vs. 13.7 +/- 2.7 mN/mm(2) for right and left Ventricular trabeculae carneae, respectively in 2.5 mM [Ca2+](o) at a 0.33 Hz stimulation frequency. Time to peak tension (405 +/- 21 vs. 4 05 +/- 32 ms), time to 50% relaxation from peak contractile response ( 277 +/- 21 vs. 278 +/- 14.6 ms) and time to 80% relaxation (428 +/- 29 vs. 433 +/- 22) were not different between right and left ventricular trabeculae carneae. Calcium channel number determined by [H-3]PN200-1 00 dihydropyridine-radioligand binding assay was also not different (5 6.2 +/- 6.5 fmol/mg protein vs. 58.6 +/- 8.4 fmol/mg protein for right and left heart preparations, respectively). However, in myocardium ob tained from ischemic hearts the left ventricle showed a reduced number of calcium channels compared to the right Ventricle (55.3 +/- 3.5 vs. 36.6 +/- 3.9 fmol/mg protein for right and left ventricle, respective ly p = 0.027). No differences were noted in the number of DHP receptor binding sites between right and left ventricular myocardium from pati ents with idiopathic dilated cardiomyopathy (51.4 +/- 7.6 fmol/mg prot ein vs. 61.5 +/- 6.5 fmol/mg protein respectively). Our data indicate that calcium channel number is similar for non-failing left and right human ventricle. Contractile response to changes in [Ca2+](o) and freq uency were similar for trabeculae carneae from the left and right vent ricles of non-failing human hearts. Studies involving calcium channel activation or inhibition in ischemic human myocardium, where there may be differences in calcium channel number and/or function are warrante d. Whether changes in calcium channel number have biological consequen ces on contractile function remains to be determined. importantly, car eful studies of calcium channel function under in vivo conditions are warranted.