The Journal of Neurophysiology Vol. 88 No. 2 August 2002, pp. 869-878
Copyright ©2002 by the American Physiological Society

A Ba²⁺-Sensitive K⁺ Current Contributes to the Resting Membrane Potential of Neurons in Rat Suprachiasmatic Nucleus

Netherlands Institute for Brain Research, 1105 AZ Amsterdam ZO, The Netherlands

de Jeu, Marcel, Alwin Geurtsen, and Cyriel Pennartz. A Ba²⁺-Sensitive K⁺ Current Contributes to the Resting Membrane Potential of Neurons in Rat Suprachiasmatic Nucleus. J. Neurophysiol. 88: 869-878, 2002. A Ba²⁺-sensitive K⁺ current was studied in neurons of the suprachiasmatic nucleus (SCN) using the whole cell patch-clamp technique in acutely prepared brain slices. This Ba²⁺-sensitive K⁺ current was found in approximately 90% of the SCN neurons and was uniformly distributed across the SCN. Current-clamp studies revealed that Ba²⁺ (500 µM) reversibly depolarized the membrane potential by 6.7 ± 1.3 mV (n = 22) and concomitantly Ba²⁺ induced an increase in the spontaneous firing rate of 0.8 ± 0.2 Hz (n = 12). The Ba²⁺-evoked depolarizations did not depend on firing activity or spike dependent synaptic transmission. No significant day/night difference in the hyperpolarizing contribution to the resting membrane potential of the present Ba²⁺-sensitive current was observed. Voltage-clamp experiments showed that Ba²⁺ (500 µM) reduced a fast-activating, voltage-dependent K⁺ current. This current was activated at levels below firing threshold and exhibited outward rectification. The Ba²⁺-sensitive K⁺ current was strongly reduced by tetraethylammonium (TEA; 20 and 60 mM) but was insensitive to 4-aminopyridine (4-AP; 5 mM) and quinine (100 µM). A component of Ba²⁺-sensitive K⁺ current remaining in the presence of TEA exhibited no clear voltage dependence and is less likely to contribute to the resting membrane potential. The voltage dependence, kinetics and pharmacological properties of the Ba²⁺- and TEA-sensitive K⁺ current make it unlikely that this current is a delayed rectifier, Ca²⁺-activated K⁺ current, ATP-sensitive K⁺ current, M-current or K⁺ inward rectifier. Our data are consistent with the Ba²⁺- and TEA-sensitive K⁺ current in SCN neurons being an outward rectifying K⁺ current of a novel identity or belonging to a known family of K⁺ channels with related properties. Regardless of its precise molecular identity, the current appears to exert a significant hyperpolarizing effect on the resting potential of SCN neurons.