Effects of three fragments of parathyroid hormone on calcium channel currents in neonatal rat ventricular cells

Abstract

The effects of different fragments of bovine parathyroid hormone, bPTH-(1–34), bPTH-(1–84) and bPTH-(3–34), on two types of calcium channel currents in neonatal rat ventricular cells were compared in the present study. bPTH-(1–34) increased the amplitude of L channel currents, but not of the T channel currents. This effect of bPTH-(1–34) was sustained after a complete washout of the peptide from the bath. The intact PTH molecule, bPTH-(1–84), also increased L channel currents but not affecting T channel currents. While bPTH-(3–34) did not affect the amplitudes of either L or T channel currents by itself, pretreatment of cells with bPTH-(3–34) abolished the effects of both bPTH-(1–34) and bPTH-(1–84) on L channel currents. Moreover, the kinetics of L channel currents in the presence of bPTH-(1–34) or bPTH-(3–34) were different. bPTH-(1–34) increased the time constant of activation, but not of inactivation, of L channel currents from 1.8 to 2.5 ms ( P<0.05). In contrast, bPTH-(3–34) decreased the time constant of inactivation, but not of activation, of L channel currents from 159 to 117 ms ( P<0.05). These results indicate that different fragments of PTH exert different effects on the amplitudes or kinetics of cardiac calcium channel currents.