Journal of Neurophysiology, Vol 68, Issue 2 509-517, Copyright © 1992 by APS

ARTICLES

Characterization of calcium currents in aortic baroreceptor neurons

D. Mendelowitz and D. L. Kunze
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030.

1. Calcium currents in identified rat aortic baroreceptors were characterized with the perforated patch whole-cell voltage-clamp technique. Aortic baroreceptors were distinguished from other neurons by the presence of a fluorescent tracer that was previously applied to the aortic depressor nerve. The diversity of calcium currents in unidentified neurons dissociated from neonatal rat nodose ganglia were also examined. 2. A population of aortic baroreceptors (63%, 7 of 11) possessed a low-threshold, also referred to as a T-type, calcium current. This current was typically less than 100 pA in 2 mM Ca [72.7 +/- 20.9 (SE) pA, n = 7], had a rapid activation and inactivation, and inactivated completely at conditioning voltages positive to -50 mV. 3. All aortic baroreceptors possessed high-threshold calcium currents that were activated at voltages positive to -30 mV, with typical maximum amplitudes of 600-1,000 pA (826 +/- 79 pA, n = 11). 4. The high-threshold current inactivated with three exponential rates of decay of tau = 10.7 +/- 2.2 ms, 138 +/- 14.6 ms, and a third tau greater than 3 s. It was not possible to separate the kinetic components of inactivation with conditioning voltages (voltage-dependent inactivation), activation thresholds, deactivation kinetics, or calcium-channel antagonists. 5. The voltage-dependent inactivation of high-threshold calcium currents began at voltages positive to -70 mV and became steeply voltage dependent between -60 and -10 mV. Unexpectedly, the three decay constants were present after all conditioning voltages. There were no conditioning voltages that excluded any component.(ABSTRACT TRUNCATED AT 250 WORDS)

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