Stellate neurones innervating the rat heart express N, L and P/Q calcium channels.

The aim of the study was to investigate the kinetic properties and identify the subtypes of Ca2+ currents in the cardiac postganglionic sympathetic neurones of rats. Neurones were labelled with a fluorescent tracer--Fast-Blue, injected into the pericardial cavity. Voltage-dependent Ca2+ currents were recorded from dispersed stellate ganglion cells that showed Fast Blue labelling. Only high threshold voltage-dependent Ca2+ currents were found in the somata of cardiac sympathetic neurones. Their maximum amplitude, mean cell capacitance and current density were respectively: 0.67 nA, 19.3 pF and 36.4 pA/pF (n = 21). The maximum Ca2+ conductance was 51.3 nS (n = 14). Half activation voltage equalled +11.0 mV and the slope factor for conductance 11.1 (n = 14). As tested with a 10 s pre-pulse, the Ca2+ current began to inactivate at -80 mV. Half inactivation voltage and slope factor for steady-state inactivation were -36.6 mV and 14.1 (n = 9), respectively. Saturating concentration of L channel blocker (nifedipine), N channel blocker (omega-conotoxin-GVIA), P/Q channel blocker (omega-Agatoxin-IVA) and N/P/Q channel blocker (omega-conotoxin-MVIIC) reduced the total Ca2+ current by 26.8% (n = 7), 57.1% (n = 12), 25.9% (n = 6) and 69.4% (n = 6), respectively. These results show that the somata of cardiac postganglionic cardiac sympathetic neurones contain significant populations of N, L and P/Q high threshold Ca2+ channels.