The pace-maker current if in the rabbit sino-atrial node behaves as an inward current activated by hyperpolarizations, decreasing proportionally with reduced external Na and abolished by 20 mM Cs.
The study characterizes the pacemaker current (if) in the rabbit sino-atrial node, demonstrating it is an inward current activated by hyperpolarization rather than a pure potassium current.
Properties of the 'pace-maker' current if in rabbit sino-atrial node have been investigated by voltage clamp of small preparations and compared with those of the iK2 current in the Purkinje fibre. Besides having a similar voltage range of activation and responding in a similar way to adrenaline, if resembles iK2 in other respects. 2. When external Na is reduced, if decreases proportionally. In 25% Na the time-dependent current change due to if disappears. 3. 20 mM-Cs completely abolishes it. 4. The time constant of if during a hyperpolarizing voltage-clamp pulse displays a relatively high temperature dependence. 5. In spite of the similarities between the two current systems, experiments in high K solutions (48 mM) rule out the possibility that the current change seen on a hyperpolarization reflects the decay of a pure K current. 6. From conductance measurements during onset of if it is deduced that if behaves as an inward current activated by hyperpolarizations.
DiFrancesco et al. (Sat,) reported a other. Voltage clamp and ion substitution was evaluated on Properties of the pace-maker current if. The pace-maker current if in the rabbit sino-atrial node behaves as an inward current activated by hyperpolarizations, decreasing proportionally with reduced external Na and abolished by 20 mM Cs.