Characterization of calcium currents in aortic baroreceptor neurons.
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)
Mendelowitz
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Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030.
Kunze
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D000818:Animals; D000831:Animals, Newborn; D001013:Aorta, Thoracic / Q000294:innervation; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D004594:Electrophysiology; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009553:Nimodipine / Q000494:pharmacology; D009620:Nodose Ganglion / Q000166:cytology / Q000187:drug effects; D010456:Peptides, Cyclic / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010456:Peptides, Cyclic; D020960:omega-Conotoxins; C053423:Conus magus toxin; D009553:Nimodipine