Properties of the pacemaker current (If) in latent pacemaker cells isolated from cat right atrium.

Abstract

SUMMARY1. Single latent pacemaker cells were isolated from the Eustachian ridge of cat right atrium using Langendorif perfusion and enzyme dispersion techniques. Wholecell patch-clamp techniques were used to study the hyperpolarization-activated inward current (If).2. All cells studied beat rhythmically. Pacemaker activity was recorded in the voltage range -68 +1 to -54 + 2 mV and its cycle length was 901 + 67 ms (72 + 5 beats min-) at 34-36 'C. Cells were elongated with tapered ends, and appeared bent or crinkled without obvious striations. Mean cell diameter and length were 7-4+05,tm and 93-1 +5-9 jtm, respectively (n = 15). Input resistance and total membrane capacitance were 22 +02 GQ and 27-8 + 3-1 pF, respectively.3. Hyperpolarizing clamp steps more negative than -50 mV elicited a timedependent increasing inward current that was maximally activated at -120 mV.

Mechanisms underlying the cardiac pacemaker: the role of SK4 calcium-activated potassium channels

“…RyR2 and NCX-1 can be modulated by adrenergic stimulation. Indirect evidence showed that SAN cells displayed stronger and longer calcium sparks in response to isoproterenol and higher I NCX currents [89,94,95] . Molecularly, the regulation mechanism occurs through direct cAMP/PKA-mediated regulation of RyR2 [94,96] and eventually I NCX , although this latter assumption is still being debated [97] .…”

“…Alternative pharmacological approaches with SR blockers revealed modifications in the rate and the shape of the AP from guinea pig sinoatrial cells [88] . Evidence for a functional interaction between the ryanodine receptor-mediated Ca 2+ release and the cardiac isoform of the NCX-1 Na + -Ca 2+ exchanger [89][90][91] gave rise to an alternative theory, "the calcium clock", in which diastolic spontaneous Ca 2+ release activates the Na + -Ca 2+ NCX-1 exchanger in its forward mode. In these conditions, the net electrogenic inward current resulting from the entrance of 3 Na + and the extrusion of 1 Ca 2+ depolarizes the membrane of the cell toward the threshold and generates an action potential [92,93] (Figure 3, right panel).…”

Developmental changes in functional expression and β-adrenergic regulation of If in the heart of mouse embryo

“…It is well know that If increases in response to ISO in adult cardiomyocytes [1], [21]. We testedadrenergic regulation of If at -110 mV.…”

Creation of a Biopacemaker: Lessons from the Sinoatrial Node

“…This Ca 2+ release could increase the subsarcolemmal Ca 2+ concentration, thereby activate the Na + -Ca 2+ exchanger (NCX) and thus generate an inward current (I NCX ) by extruding one Ca 2+ in exchange for three Na + (Blaustein & Lederer, 1999). In 1993 Zhou and colleagues showed that after activation of I Ca,L, there was a second inward current which was due to I NCX (Zhou & Lipsius, 1993). Figure 2C shows a typical example and I-V relationship of I NCX in rabbit SA node cells.…”