Calcium Channel Currents in Acutely Dissociated Intracardiac Neurons From Adult Rats

Abstract

Jeong, Seong-Woo and Robert D. Wurster. Calcium channel currents in acutely dissociated intracardiac neurons from adult rats. J. Neurophysiol. 77: 1769–1778, 1997. With the use of the whole cell patch-clamp technique, multiple subtypes of voltage-activated calcium channels, as indicated by measuring Ba2+ currents, were pharmacologically identified in acutely dissociated intracardiac neurons from adult rats. All tested neurons that were held at −80 mV displayed only high-voltage-activated (HVA) Ca2+ channel currents that were completely blocked by 100 μM CdCl2. The current density of HVA Ca2+ currents was dependent on the external Ca2+ concentration. The Ba2+ (5 mM) currents were half-activated at −16.3 mV with a slope of 5.6 mV per e-fold change. The steady-state inactivation was also voltage dependent with half-inactivation at −33.7 mV and a slope of −12.1 mV per e-fold change. The most effective L-type channel activator, FPL 64176 (2 μM), enhanced the Ba2+ current in a voltage-dependent manner. When cells were held at −80 mV, the saturating concentration (10 μM) of nifedipine blocked ∼11% of the control Ba2+ current. The major component of the Ca2+ channels was N type (63%), which was blocked by a saturating concentration (1 μM) of ω-conotoxin GVIA. Approximately 19% of the control Ba2+ current was sensitive to ω-conotoxin MVIIC (5 μM) but insensitive to low concentrations (30 and 100 nM) of ω-agatoxin IVA (ω-Aga IVA). In addition, a high concentration (1 μM) of ω-Aga IVA occluded the effect of ω-conotoxin MVIIC. Taken together, these results indicate that the ω-conotoxin MVIIC-sensitive current represents only the Q type of Ca2+ channels. The current that was insensitive to nifedipine and various toxins represents the R-type current (7%), which was sensitive to 100 μM NiCl2. In conclusion, the intracardiac neurons from adult rats express at least four different subtypes (L, N, Q, and R) of HVA Ca2+ channels. This information is essential for understanding the regulation of synaptic transmission and excitability of intracardiac neurons by different neurotransmitters and neural regulation of cardiac functions.