Evidence for two types of calcium currents in frog cardiac sinus venosus cells

✍ Scribed by P. Bois; J. Lenfant

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 621 KB
• Volume: 417
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00372956

✦ Synopsis

Two types of calcium currents were recorded in single sinus venosus ceils of the frog heart, using the whole-cell patch-clamp technique. The threshold potentials were approximately -65 mV for T-type current and -40 mV for L-type current. The amplitude and time course of T-type current were unaffected by exchanging calcium for barium, while the amplitude of L-type current was increased and its decay slowed. T-type current was neither modified by 10-6M nifedipine nor by 10 -7 M isoprenaline in contrast with the effects of these agents on L-type current. T-type current began to inactivate at -90 mV and was fully inactivated at -45 mV. Its steady-state inactivation curve was approximately 35 mV negative to that of L-type current. Overlap of activation and inactivation relationships was present for both T-and L-type currents and was maximal at -57 and -30 mV, respectively. It was concluded that T-and L-type currents can easily be separated by their voltage, kinetic and pharmacological differences. The presence of a high density of T-type current may be correlated to its contribution to the pacemaking function of the sinus venosus ceils.