MEMBRANE-PROPERTIES OF AREA POSTREMA NEURONS

Intrinsic membrane properties, voltage-dependent sodium and voltage-de pendent potassium currents of area postrema neurons in culture have be en characterized with respect to their voltage dependence, time depend ence and sensitivity to specific blocking agents. The area postrema is a hindbrain circumventricular organ which is known to have an importa nt role in the central regulation of cardiovascular function. This stu dy is the first to describe the biophysical properties of ion channels present in rat area postrema neurons. Recordings in current-clamp mod e revealed a mean resting membrane potential of -55.0 +/- 1.6 (n = 24) mV and an input resistance of 213.6 +/- 23 M Omega. For the 24 neuron s tested, the evoked action potential had a mean threshold of 38.8 +/- 2 mV and a mean amplitude of 107.3 +/- 15 mV. Our results show that t he area postrema possesses only one principle sodium current which is completely abolished by 5 mu M tetrodotoxin (TTX) (n = 28). This curre nt activated near -50 mV and reached peak amplitude at -30 mV. The are a postrema does not possess a TTX insensitive sodium current. The area postrema has at least two types of potassium currents. All area postr ema neurons studied with tetraethylamonium (TEA) (n = 40) showed the p resence of a slowly activating outward current which was present at vo ltages greater than -40 mV and was blocked by 10 mM TEA. In addition, 75% of the neurons studied (n = 30/40) also showed a rapidly inactivat ing, 4-AP sensitive IA type current which activated near -30 mV. Angio tensin II attenuated both the peak and the steady-state potassium curr ents, suggesting that angiotensin II may modulate area postrema activi ty by inhibiting voltage-gated potassium channels.