Key Points
- To examine how isoprenaline, carbachol, and cesium ions affect intracellular sodium activity and spontaneous pacemaker action potentials in rabbit sinoatrial node preparations.
- Isolated multicellular tissues and single pacemaker cells from rabbit sinoatrial nodes.
- Measured intracellular sodium activity using double-barreled sodium-selective microelectrodes and the fluorescent indicator SBFI during spontaneous beating, pacing, and pharmacological interventions.
- Isoprenaline increased intracellular sodium activity from 4.7 ± 1.2 to 5.5 ± 1.6 mM (n=16, P < 0.01) and shortened action potential cycle length from 338 ± 46 to 269 ± 35 ms (n=16, P < 0.01).
- The hyperpolarization-activated inward current blocker ZD-7288 decreased intracellular sodium from 5.2 ± 1.0 to 4.6 ± 1.3 mM (n=4, P < 0.01) and prolonged cycle length from 394 ± 20 to 553 ± 68 ms (n=4, P < 0.01).
- Carbachol and cesium ions significantly reduced intracellular sodium to 3.9 ± 1.2 mM (n=15, P < 0.01) and 3.9 ± 1.3 mM (n=18, P < 0.01), while prolonging cycle lengths to 587 ± 100 ms and 464 ± 87 ms, respectively.
Structured PICO
PPopulationMulticellular and single cell preparations isolated from rabbit sinoatrial (SA) nodes
IInterventionIsoprenaline, carbachol, Cs+, and the If blocker ZD-7288
CComparatorBaseline conditions prior to drug application
OOutcomeIntracellular Na+ activity (a(i)Na) and action potential cycle length (ACL)surrogate
Isoprenaline, carbachol, and Cs+ modulate intracellular Na+ activity and action potential rate in rabbit SA node cells, likely by affecting the hyperpolarization-activated inward current (If).