Abstract: Objective To examine the characteristic of L-type calcium current(I_Ca.L) in three distinct canine right ventricular myocytes and the response to isoproterenol.Methods Using whole-cell patch clamp techniques to examine the electrophysiological characteristics of I_Ca.L of myocytes enzymatically dissociated from canine right ventricular epicardial,midmyocardial,and endocardial,and to study the difference of current-voltage relations before and after using isoproterenol.Results The peak density of I_Ca.L(pA/pF) was-4.868±1.362(n=20),-3.594±0.544(n=20),-2.874±0.547(n=20)(F=33.493,P<0.05) in right ventricular(RV) epicardial,midmyocardial,and endocardial myocytes(P<0.01),respectively.Perfusion of Iso(0.5 μmol/L) increased peak I_Ca.L densities from-4.838±1.127(n=11) to-22.348±4.057(P<0.01) in RV epicardial myocytes,-3.726±1.051(n=11) to-17.992±4.159(P<0.01) in RV midmyocardial myocytes,-2.714±0.879(n=10) to-2.987±1.012(P>0.05) in RV endocardial myocytes.Conclusion Iso can significantly increase I_Ca.L densities peak on the Epi cells and M cells,but M cells and the Endo cells present no response to the drug.β-adrenergic agonists can reduce outward shift in the current active at the end of phase 1 of the right ventricular epicardial action potential.

Key words: electrical heterogeneity, L-type calcium current, whole-cell patch clamp, isoproterenol