Experimental physiology
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Experimental physiology · Jan 2001
Raised extracellular potassium attenuates the sympathetic modulation of sino-atrial node pacemaking in the isolated guinea-pig atria.
Intense exercise or myocardial ischaemia can significantly increase both the concentration of extracellular potassium ([K(+)](o)) and cardiac sympathetic nerve activity. Since changes in [K(+)](o) modulate membrane currents involved in sino-atrial node pacemaking, in particular the voltage-sensitive hyperpolarization-activated current (I(f)), we investigated whether raised [K(+)](o) (from 4 mM to 8 or 12 mM) could directly affect the heart rate response to cardiac sympathetic nerve stimulation (SNS). In the isolated guinea-pig atrial-right stellate ganglion preparation, raised [K(+)](o) significantly decreased the maximum diastolic potential, amplitude and maximum rate of rise of the upstroke of sino-atrial node pacemaker action potentials in 8 and 12 mM [K(+)](o) (P < 0.05). ⋯ In conclusion, extreme physiological levels of [K(+)](o) attenuate the positive chronotropic response to cardiac sympathetic activation due to decreased activation of the I(f) current. This is consistent with raised [K(+)](o) protecting the myocardium from potentially adverse effects of excessive noradrenaline. Experimental Physiology (2001) 86.1, 19-25.