pacemaker activity involves interplay between several ionic currents that influence spontaneous diastolic depolarisation of the sinoatrial node
these currents include the If current - the 'f' denotes 'funny' - called this because it had unusual properties compared with other current systems known at the time of its discovery
If current is carried by both sodium and potassium ions across the sarcolemma
the If current is inward at voltages in the diastolic range
activated on hyperpolarisation (within the diastolic range of voltages regularly observed in cardiac pacemaker tissue)
characterised by unusually low single-channel conductance and slow activation kinetics
directly activated by intracellular cyclic adenosine monophosphate (cAMP) - the If is not linked to cAMP-dependent phosphorylation activity and is carried by the hyperpolarisation-activated cyclic nucleotide-gated family of ion channel
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