Elecropharmacology of Taurine on the Hyperpolarization-Activated Inward Current and the Sustained Inward Current in Spontaneously Beating Rat Sino-Atrial Nodal Cells

Abstract

Abstract. Modulation by taurine of the pacemaking activity and the underlying ionic currents, especially a hyperpolarization-activated inward current (I f ) and a sustained inward current (I ST ), in rat sino-atrial (SA) nodal cells was investigated at different pCa levels using a patch-clamp technique. Increasing pCa levels from 10 to 6 stimulated the spontaneous activity and simultaneously increased the I f . Application of taurine depressed more strongly the spontaneous activity at higher pCa levels. At all pCa levels, however, taurine (20 mM) increased the I f by 60.1 ± 1.7% (n = 8, P<0.001) at pCa 10 and by 48.0 ± 1.4% (n = 8, P<0.01) at pCa 7. At pCa 7, taurine (10 and 20 mM) decreased the sustained inward current (I ST ) by 13.3 ± 1.1% (n = 5, P<0.05) and by 38.1 ± 2.4% (n = 5, P<0.01), respectively. Taurine (20 mM) inhibited the L-type Ca 2+ current (I CaL ) by 35.8 ± 2.5% (n = 8, P<0.01), whereas taurine enhanced the T-type Ca 2+ current (I CaT ) by 29.3 ± 2.9% (n = 8, P<0.05). Also, taurine at pCa 7 decreased the delayed rectifier K + current; taurine at 20 mM inhibited the rapidly activated K + current (I Kr ) by 55.6 ± 3.3% (n = 6, P<0.001), but not the slowly activated K + current (I Ks ). Taurine often elicited dysrhythmias, dependent on taurine's concentrations and pCa levels. These results indicate that taurine causes a negative chronotropic effect due to the inhibitions of the pacemaking ionic currents such as I CaL , I Kr and I ST , and suggest that the I f and I CaT currents make a minor contribution to pacemaking activity in rat SA nodal cells.

A Model of Cellular Cardiac-Neural Coupling That Captures the Sympathetic Control of Sinoatrial Node Excitability in Normotensive and Hypertensive Rats

“…The T-type Ca 2þ current as an inward current is involved in pacemaker depolarization, as demonstrated by the slowdown in pacemaker activity when it is blocked (54,55). The blockade of I CaT increased the CL of the AP by only 15.6% in the model, a result that is consistent with the experimental data from Hagiwara et al (51,52) and Satoh (56). However, it is important to note that the contribution of I CaT to pacemaker activity is controversial, and a wide range of experimental results have been reported (55,(57)(58)(59).…”

Cardiovascular Complications of Energy Drinks

“…A significantly increased QTc interval in healthy young subjects, as well as those with a preexisting genetic long QT syndrome, has been reported in association with consumption of EDs. EDs contain many ingredients in addition to caffeine including taurine, often present in high amounts, which is known to work on multiple cardiac ion channels and in certain circumstances can be arrhythmogenic [45].…”

Regulation of basal and reserve cardiac pacemaker function by interactions of cAMP-mediated PKA-dependent Ca2+ cycling with surface membrane channels

“…The Ca-dependent increase of I f and shift of I f activation curve in a positive direction was initially explained by a direct effect of [Ca] i on the I f channel [99, 100]. However, experiments using inside-out macropatch techniques failed to show a direct effect of [Ca] on the I f current in rabbit SANC [101].…”