AREA POSTREMA VOLTAGE-ACTIVATED CALCIUM CURRENTS. Hay, Meredith, Eileen M. Hasser and Kathy A. Lindsley. Department of Physiology, University of Texas Health Science Center, 7703 Floyd Curl Dr., San Antonio, TX 78284-7756 and Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.
APStracts 2:0256N, 1995.
SUMMARY AND CONCLUSIONS
1. Calcium currents in rabbit area postrema neurons were studied with the perforated patch-clamp technique. Experimental conditions eliminated Na + and K + currents and identified both low- and high-threshold voltage-activated calcium currents. 2. Low-threshold, T-type calcium currents were observed in 64% of the area postrema neurons recorded. This current activated near -60 mV and had an average peak amplitude of -36.2 + 5 pA at -40 mV. This current began rapid inactivation near -95 mV, reached half-maximal inactivation at -71 mV and was totally inactivated by -40 mV. 3. A high-threshold transient current was recorded in all area postrema neurons which consisted of both a transient and sustained component. This current was present at voltages greater than -40 mV and the transient component of this current was responsible for the majority of the total Ca 2+ current. 4. Nickel ions (10 [mu] M) effectively reduced both the T-type current and the high-threshold current. Cadmium ions (100 [mu] M) effectively reduced the high-threshold current while having insignificant effects on the low-threshold current. 5. Application of the dihydropyridine antagonist nimodipine (1-10 [mu] M) had no effect on either the low- or high-threshold voltage-activated calcium Ca 2+ in area postrema neurons. In addition, application of w -conotoxin-GVIA (2-10 [mu] M) was also without effect on either the low- or high-threshold voltage- activated Ca 2+ current, suggesting that area postrema neurons possess neither L or N-type voltage-activated Ca 2+ currents. 6. Application of w -conotoxin MVIIC (10 [mu] M) significantly inhibited the peak high-threshold Ca 2+ current by 65.4% suggesting that area postrema neurons do possess a w - conotoxin MVIIC-sensitive high-threshold Ca 2+ channel. 7. Arg-vasopressin (150 nM) significantly increased the transient component of the high-threshold Ca 2+ current but had little effect on either the low-threshold or the high- threshold sustained component. 

Received 11 May 1995; accepted in final form 10 August 1995.
APS Manuscript Number J318-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.