The Journal of Neurophysiology Vol. 77 No. 4 April 1997, pp. 1769-1778
Copyright ©1997 The American Physiological Society

Calcium Channel Currents in Acutely Dissociated Intracardiac Neurons From Adult Rats

Seong-Woo Jeong¹ and Robert D. Wurster²

¹ Department of Physiology and ² Departments of Physiology and Neurological Surgery, Loyola Stritch School of Medicine, Maywood, Illinois 60153

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 -conotoxin GVIA. Approximately 19% of the control Ba²⁺ current was sensitive to -conotoxin MVIIC (5 µM) but insensitive to low concentrations (30 and 100 nM) of -agatoxin IVA (-Aga IVA). In addition, a high concentration (1 µM) of -Aga IVA occluded the effect of -conotoxin MVIIC. Taken together, these results indicate that the -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.

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